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The weathered rocks of Hong Kong Cummings, John Moss 1935

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; i l ,<— i L 'f . ! " • Vf. t & J . D . L . L I D ! ? , 4 >s. t • ' I £ | acc. ,, THE W&AIHKBKD BOOKS' OF HOKQ- KQBG-Joh.ii Moss Qunaaings A THESIS Presented in Partial Fulfillment of the Bequirements for the.Degree of MS2BR OF APPLIED SCIEICE in GEOLOGICAL EH&IIvESSIEG Voiume One April 1935 IEDBX mum obe Introduction 9 a • « »• » a • a' a •«• a a a a a a < Introduction Acknowledgments . . . . . . . . 9 . . . . . . . . . . Geology of Hong Kong 4 . . . . . « Chapter One - General Bock Weathering Intro&uctxon « • • « . • . . . . . . . . . . . . . . . . . . . . . . . . . . She Proe©sses of Y/eatherigg • • • . • * • . . . . • « . . * • Sfechanic&l Weathering ( ex.) XnSOl&tiO&l .•»:«'»*..««'.* «». • » . « * * » * • « • . 0 « » a (b) Sspansioa of water on freezing . . . . . . . . . (c} Work of Organisms . . . . . . . . . . . . . . . • • • • • * . (d) Other fiechanical Agents Chemical f e a t h e r i n g . . . . . . . . . (a) Composition of the atnjosphere . . . . . (1) Ritro gen,Ei trie Ac id, and Ammonia (2J Carbonic Acid * (5} Oxygon . . . . . . (4) Other Components . * . « • (b) Solubility of Minerals . . . . . . . . . . . . (c) Decomposition of Silicates . . . . . . . . (d) Colloids » 9 v . .a.* .-. , a e . . . . . o e . . . . . . « .ILnxulsoxds * . ' . . « . * • . . « . . . « « * . . . . « . - • fiels aaa^aaaaaaai • a • a a a a « a a 1 0 * » « e • e o « • • » • • » » » • » « «o e«>»*•«» « • a « « • * 0 a •« a e • -a  a a page 1 « » « « a 5* 6 *r a a " 6 a * -a • ft « 9 a • a a a 10 < D • • « " 12 e o « » " 13 * « 9 0 -S [t 14 0 A O a • t! 15 a • a a a n 15 « « e • e " 16 » a « a a " 16 a a a a a " 17 a a a a -a 17 a a a e e « IV a a a a a " 17 • « a a a 20 a a a a a " 23 " 25 e a a a a M 25 "ur « *» 2S a a a a a " 27 Precipitation of Colloids . . . . . . . . . . Solution,Transportation and Precipit-ation of Iron and Silica Composition of the Soil Colloid . . (e) Weathering Processes (1/ Oxidation (2) Carbonation . . . (Sj Hydration Hydrous oxides of Iron . . . . . . Hydrous Aluminium Oxides Hydrous Silicates . . . . . . . . . . . . . . . . . . . . . " 41 (fjDecomposition of Specific Minerals Vfeatheriog of Orthoclase " 48 Decomposition of Plagioclase . . . . . . . . . . . . " 50 Decomposition of Micas " 51 Weathering of Amphiboles and Pyroxenes . . " 52 Weathering of Olivine . • • • • « • . • * • • » • • . • • > • " 54-Accessory Minerals • • • . . . . . • • • • . . . • « . . . . . " 54 ixephsizne . . . . . . « » . . . . . « . « . . . . .«a«. . . . . . . . ' • 90 . e o 1 9 ft. 1 . 9 . 9 9 9 9 9 « .9 O * 9 9 9 9 9 9 9 « 9 9 <9 '9 -9 '9 9 9 9 . 9 >.« « 9 9."9 9 9 '9 .9 9 9 »-9 9' 9"'.:« 9 9 9/9-9 9 * 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 * 9 9 9 . 9 9 9 9 9 9 & «tt 9 999 9 9 9 9 9 9 9 9 « 9 9 9 28 31 32 35 £$5 36 39 It KQ • « « t • • • t • a * e • • t 000 • • « • 0 9 6* t • o a o 0 0 a • 0 ® 0 o » 0 0 ft 0 62 ft A 5? «'d • e « o © » © « • « o # © a © « a .9 KjSm> « A^ n 000000000000000-6 e« • • » « Uw O Ail e « » « •««««« « » » «« • « ft * « > . ** AA « * » e & « « « 0 e, # c « * 0 * -9 » 4 e w**/ n AH A7 O 0 • 0 O * • ft O 0 e 0 0 0 0 « O 0 0 « # -0 W I Ig)Studies of the Solubility of Soma Silicate Minerals . . .page 56 Weathering of Specific Bock; Types Granite « « • • » » » . » • • • » • . » « » • » » • < Sranodiorite • » • • • • • • » • • « . « • » • ' Hepheline Syenite . . . . . . . . . . « « > Phonolite . « »»» . «»« . «« . .<> .« . »» ' 3{XS£tltS » # » 4 « a I. w » # o # » -a » . « # »-B * « . ® ' Dios'ite • « » • • » • ® a » . o • • • « « s . . . . . . ' ultra. 3asic Hocks • » • « . . . » . . . . . . < OSi'HER W O tropical Weathering; Bauxite and . Laterites Istroduc tioii » » * » • • • . . « » . . * . » . • « a o «.»»»»«•• »'•••••.•»'.• •»• •» . . » » « • » '* 72 Laterite;Definition and Classification w 74 Physical Character of Laterites . . . . . . . . . . . . . . . . . . . . . . . . . . . . " 78 Elineralogic Constituents of Laterites . . . . . . . . . . . . . . . . . . . . . . 80 Chemical Cnaracter of Laterites " 81 Alumina «:»«»«.».«««••.»*...*««.;«.»«».••»»••.•««».«.-*•• «-».»• " 84 Ferric Oxide . • .»••»•»••••»•••.•«••»••*-• »'••:»••••••••••*««•••• ® 11 87 Silica . •«»..»» « » « . . * « ® ..»•.» o »«. . . . . . . . . . e .o . . . » . «® « SB Lx thoniar^e . . « ® . « . » . * • « * « . . . . . . . « • » • • . « .# . . .. . .»•«. ^ 89 VfSter a . . « . e • ® » « * . « . b . » » . # e »'» • c « » » ® . » . . . « « * « « ^  » " » . ® •« w « . ft * « . . " SO 'jjypical Occurrences . . . . . « . « • . . . . » » . * • • < • » . . • « » . » » • « . . . » » » « . « " 91 Laterization in Sierra Leone . . . . < > . . . . . . . . « . . . . . . . • • . . . . . . M 31 Rhodesian Laterite » • • • • « • • « » • • » • « « « « » » • « « « • » » • « » « » » • . • » • » " 92 Laterite in «*estern Australia " 92 Laterite in British Guiana . . . . . . . o . . . * * 2erro Rcxa in Sao Paula,Brazil tt 97 Lateritic Deposits of I^Dsarabique . . . . . . . . . . . . . . . . . . . . . . . . . " 98 Lateri tic Deposits of India " 99 Laterite and Bauxite in Germany . . . . . * . . * . . . • • . . . . . . « . . > . . " 102 T'he Bauxite Deposits of Arkansas " 103 Bauxite and Aluminiusi 104 Origin of Laterites and Sauxites " 106 Lacustrine Origin . • * •««»»•.».• ® . « « . » • . . . « . . . . . . . . . . . . . . . . . * M 106 Action, of Atmospheric and Organic Acids n 107 aicro-Grganisms ® • . . . . . • . . . . . . . . . . . . . . . « . . . . . . . . . . . ^ 107 Hot . . . . . . . . . . . . . . ^ 108 Deposition by Uossard Subterranean Vts>t@rs • • 0 0 0 00*00-0 000 0 -0 0 108 « -0 0 « '0 '0 0 « • 0 0 * 0 * 0 0 0 0 0 0 • «0 S 9 0*-*«»4 * « 0 * 0 » * 0 0 0 0 0 0 0 0 0 0 0 -0 Origin oif* Li&oX 121 • *»# 0 «© # »®»«®* 0 « e * « 0 0»® * 0« ^ . 119 fhe Color of H0U. » 0 0 0 9 0 0 * 0 0 « 0 0 0 0 0 0 « 0 » « 0 « « 0 0 0 ' 0 0 0 « » . 0 « ' 0 0 « « ^ 1^0 Blblio^rsphy a 0«»®» «0 « » « » 0 » « « • « « »«»« ® 0«• « *»0 • ®»«*>»o»• ®«® • * —ooo ILLUSTRATIONS Chapter One- general Bock Weathering Diagram Illustration results of l e a t h e r i n g , — . » « * » * . p a g e 12 ..Seat heri pg * Late rites and Bauxites. . Magysms-j . Classification of Laterites * 7fi . Diagtaawilo .Section of part of typical. laterite plateau mitli M u x i i s » 101 Diagram illustrating- circulation of water in laterite mantle * 11-5-1.1 g Maps: Slap. l~ Bauxite occurrences of Africa " 91-92. SapB- " » of South America . . . . . . . . . . . . # 95-96 n " of M i a ' » 99~1Q0 •.Sap 8- " * . .of .Surops * * * 102-103 " * of the United States . . . . . . . " 105-104. O0O IK2S02UGTI0K I Introduction : ,j The following study of a number of weathered specimens from the I j ..... . , • . . • . . [\ vicinity of Hong Kong was undertaken at the suggestion of Dean R.W.Brock i of the University of British Columbia/ j During the course of field work in this area .Dean Brock was struck ! with tho possible interest which might attach to the widespread weatered •y • • -j.j \ • - . - .. - • \ ! products of the region,products of not only interesting occurrence,but formed under rather unusual climatic conditions.He consequently obtained samples of a number of the more interesting types,and on his return in April 1333 to Vancouver,submitted them to the Kockfeller Institute at Wis-consin for detailed analysis. The writer commenced an examination of this material in the fall of j 1934,the present thesis embodying the woric of two sessions. : Before actually attacking a specialized problem such as this it w:i.s found necessary to become thoroughly familiar with the literature of weat-hering in all its ramifications.In this connection son© 150 references were consul ted,and in view of the wealth of general information thus obtained,it i was felt that an organized summary represented by Chapters 1 and 2 of the j . present thesis ,would prove invaluable to anyfuture student of weathering. I In general the impression gained from existing literature on this subject is one of indefiniteness and uncertainty,very often resultant upon loose definition,and unfortunately,in many instances,upon the tendency to theor-ize at the expense of intelligent laboratory work.The following excerpt from "The kaolin Minerals" by JIoss and Xerr(0.S.G.S.Prof.Paper lS5-i£ ,1931J Gives an excellent review of the situation. "The identity and properties of the minerals of clays have long inter-estsd mineralogists,persons engaged in the industrial use of clay materials ,and students of soils.Although many workers have devoted time to the study of these minerals,the conolusions reached have varied widely,and no satis-factory classification has been presented.-There has been a general lack of reliable criteria for the recognition of species,as is shown by the conflict-ing results of different investigators .A large nurabervof names that have proposed for the clajr minerals have not been generally accepted,and others are in use for v;hich no firm foundation exists.Furthermore the Inadequacy of the early methods of study make it practically impossible to correlate most samples of clays with the accounts of their properties as given in the literature.Descriptions of clay minerals written before 1900 or even later are with a few notable exceptions of little value jud-ed by the present-day standards,and aany of the early descriptions are worthless and even mislead-ing.'ibis situation makes obvious the need for a resurvey of the clay minerals by modern .methods "It is only within the last 10 years that methods have been perfected which permit the detailed study of minute crystal aggregates,mating it pos-sible to obtain definite information from the optical examination of even the finely divided clay minerals.Of equal importance has been the develop-ment of the X-ray powder method for studying fine-grained crystalline mater-ial in random orientations.Coordinated studies by optical,X-ray.chemical,and t thermal methods now yield criteria for the identification of the c|iy miner-als which are far superior to those based solely on chemical methods,as was the practice when these minerals were first described.Such criteria material-ly alter the conclusions reached by the former methods of study,necessitating the ^interpretation of the minerals of icaolin in the light of recent develop-1 1 j nents,and it is upon an investigation of this type that the present report • ? •j • . is .'based;." . •Ihe foregoing remarks m y be equally extended to cover all the prod-j acts of weathering. J The writer was faced with tho problem of studying a complex material, .! or materials,by entirely inadequate methods,and for this reason much of the ' work embodied herewith is of necessity indefinite and theoretical.Although I' •••• • .v. , j! unfortunate,if this thesis is considered as a preliminary examination in 'IJ .......... . . . . . . . . . . . . . 7 ... ' . . ' ij which an attempt has been made to give,not only the meagre few facts defin-• ! itely obtainable ,but to stimulate interest,raise controversy,arid where poss-| ible point out possibilities for fixture research by adequate methods,its pur-;! pose has been fulfilled. ;| Ehe analyses obtained from the Sockfeller Institute proved invaluable j ,and indeed,were the only definite information obtainable in the case of . j • - .• • : several samples.Although thb analyses,in themselves,are very instructive,it < - . - . • 1 is felt that too much reliance should not be placed in any of the calculated mineralogic compositions.In a general sort of way such minerals as llmonite ,calcite,etc. are likely to be approximately correct.vhen dealing with the various combinations of alumina,si1ica,water,and even the alkalis,the accuar-aCy of the assumptions -rnde is often very questionable.Among the older wor-kers it was common to attribute definite molecular combination to all the constituents presentSvjhereas subsequent work has shown the alasost ubiquitous occurrence of colloidal mixtures,in which more or less of the alkalis are usually adsorbed.Even the mineral kaolinite.possessed of definite crystallo-graphic properties,shows a variation in its silica-alumina ratio from 3 :1 to below Si1 in different samples.Another interesting development of recent II tines has been the discovery that mack of the so-called sericite.conffiianly developed upon weathering of the felspars,is not mica at all but possesses the fommia of Icaolinite less one molecule of water.It would appear,in fact that; a series ,dependent upon the removal of potassium during alteration, exists,marked by a decreasing birefringence from true sericite to kaolinite. In consideration of thes<s points,as vrell as others,the falley of attempting to arrive at any definite mineralogio determination by calculation is appar-ent.If this is understood ,ho*rever ,at the out set, the calculations are not without value,in that they do give sous indication of the quantity of a few minerals rather definitely,and in the case of others nay indicate possible direction for future vtoVk.* Considerable experimentation was necessary before a satisfactory tech-nique v,as acquired for the preparation of thin sections of friable material. When this accomplished,however,anotter valuable aid was at hand to fur-ther the study of these specimens.The microscope,although proving extremely necessary ina general way,fell down rather badly r.hen it was called upon to determine the optical characteristics of many of the secondary Mnerals en-countered. She re were two raajor reasons for this? the first that in many cas-es th® secondary compounds were too small and too intimately intermixed for snore than a few,usually quite undiagnostic properties to be determined; the second,that isany minerals are so poorly and loosely described in the litera-ture, that even were a full determination possible,difficulty would be encount-ered in correctly relegating it to its propsrcplace.Thanks to the work of Boss and Kerr isrithin the last few years,the situation is much clarified with regard to the hydrous aluminium silicates,and it is to be fervently hoped that their valuable work srill be continued to cover allied substances such .-•' 5. as the hydrous aluminium oxides and hydrous iron oxides® 4 certain amount of chemical examination,as well as ths use of heavy solutions,grain picking etc® were used by the writer,largely without satis-factory results. In general ,however,enough of interest was encountered in the examin-ation,to make it heartily recomnand&ble that further work,by adequate means be carried on upon these specimens.It appears,without doubt,that Dean Brock' s original Interest was fully justified,and that with detailed examination some rather unusual features might appear. As emphasized before the present thesis,although containing a certain amount of useful data,must,of nesessity,be regarded as of the most prelimin-ary nature .However Kiargr interesting conclusions were arrived at,sons morearr less speculative,othere more definite,which should justify the existence of the. paper®. • . o. Acknowledgements.* In the preparation of this thesis considerable aid was received from all members of the Faculty of Seology,especially Bean H.ft* Broclc and The writer would also like to take this opportuenity to thank Messrs.Buller and Robinson for their patience in discussing different as-pects. of the paper. Seo logy of Hong Kong It is usual,in a paper such as this ,to include information of a general nature in respect to the geology,climate,etc. of the area from vzhich the specimens were brought.ffiie writer,under the circumstances dis-cussed below,prefers so not to do. Had it been possible to make a personal field examination,or had the time been available to co-operate with Dean Brook in making full use of the geological information obtained by him,this thesis would ideally comprise a combination of both field and laboratory data.It is feIt,however, that sufficient information has been accumulated from the laboratory examin-ation of the specissens alone to constitute a unit in itself,and as it has always be^n the writer's experience that it is difficult to really compre-hend a situation from second-hand information alone,he has preferred to deal with only the tangible material available for study at first hand,and leave to others more qualified the task of relating field work toi;laboratory study. For this reason this paper is presented solely as a laboratory report, excepth that a comprehensive review of the literature on weathering is inc-luded as an aid to the reader,not only in helping to clarify his ideas on z • the subject matter of the present paper,but as a not invaluable compilation to any future student of weathering® Prom this point of view the addition of general information upon the geology of Hong Kong,etc.,would be in the nature of "padding" and beyond tte scops of this thesis. Specimens Studied Hong Kong Granite . : iQ. « Fresh lock K2 - Decomposed 2' down below surface. £3 - Decomposed at surface. £4 - Completely decomposed - SinDrinker's flay. ?2S - Bauxite ,Shap Pat-Seung Valley B 341 3 - Hong Kong Sranite-near Irae Mud Pass,weathered to kaolin? but texture preserved, 3341 A - ditto but texture gone. ffai Po Qranodiorite V37A - fresh rock ¥373 - Partially decomposed. V37C - Hore completely decomposed. V2I-2 - Lateritic clay from ¥57 Lamprox>hyre Dike VIII 29 A - Fresh lamprophyre VIII 29 B - Partially decomposed VIII 29 0 - Completely decomposed II •Sraaito Bike VIII 29 D - Fresh rock VIII 29 3 - Completely decomposed but texture preserved. VIII 29 F - Completely decomposed to brown earth Tai Mo Shan Porphyry TK 1 - fresh r o c k m i l e east of flag Kan •IS 2 - concentric zone of decomposition-ball from edge of fresh . rock. • • • • • • 3 2 - fresh rock Q 1 - weathered to brown clay Volcanic Socks S343 A - fresh (Repulse Bay) 3343 B - decomposed crust ( Hepulse Bay) 3 320 - kaolin frota volcanic (Repulse Bay) near T&i Po. 3 321 A. - Itocity Harbour -fresh rock .3 321 B - " " — decomposed crust. -Two additional specimens of Hong Song granite wers examined4although analyses were not available -these are B 429-decomposed granite from wave-cut terrace,and B430,less decomposed speciman from same locality. Hote:-the above descriptions are those of Dean R.W.Brock QBilPgSB, DIE asiaML BOGS W M g i M u m 9 ' ' The universally rmnifested disharmony between natural objects and their enviroment is not confined to organic beings. Every mass of rock exposed by diestrophism"or denudation, or erupted as molten matter from the earth's interior, finds almost at once that its various elements arc in disharmony with their surroundings. Although complete equilibrium is seldom, if ever, attained there is continuous reaction taking place towards this end. Climatic aad atmospheric agencies com-bine their forces,, both physical and chemical; a breaking.up easues, succeeded by new combinations and perhaps reconsolidations more in keep-ing with existing circumstances. She intermediate product in the endless cycle of change, this continual striving towards equilibrium with envir-onment ,is the loose superficial mantle of debris which nearly everywhere covers the land-disintegrated and more or less decomposed rock material,, intermingled with organic material,commonly known as the soil.. The whole story of rocks is one of a continuous transformation from the unstable to the more stable? a constant striving after harmony with environment,an environsmnt which related to any unit of the earth's crust,itself is variable.The result is that the process of change which began with the origin of raattor.continuss,destroying,tearing do^n,simp-lifying in one place,integrating and building up in another. The term"weath6ring" is reserved for those processes,both physical and chemical,which normally modify, rocics exposed to surface conditions. These processes are destructive„their action being manifested in the mechanical simplification of these rocks,^s weil as the formation of less complex chemical compounds. 10 • •Those integrating processes ^attendant upon increase of temperature and pressure ,'tvhich tend towards greater complexity of cosrposition»are knov/n variously as "anarnorphic" and "i5»etasEorphic"« In this connection it sight be pointed out thai the terminology is somewhat Indefinite®In order to avoid confusion,the usage of fan Rise ?;ill be adhered to in this papero Van His®* uses the terra "s&taisorphic" to cover all changes within a * A freatise on ISstamorphism -Mon.47.U.S.S..S, 1904 „¥an Hise system brought about by variations in environncntjboth constructive and. destructive action is thereby included, under this definition,those processes tending to add to the complex-ity of a system are called "anamorphic",*rhile those which are ox a disin-tegrating or decomposing naturewhether resultant -upon weathering or the action of thermal solutions,are classed as rtlsatamorphic"« She -Prooess e s of V/eaths ring In the course of adaption to environment,a rock is acted upon by both, physical and chemical processes.although it is possible to conceive of a sot of conditions 'chore one is present to the exclusion of the ofiher,normally both act contemporaneously,each mutually augmenting the other. In general these forces are superficial,working from v/ithout,downwards• The decomposing forces bocome inert at relatively shallow depths,ond it is only through the radium of active erosion that thousands of feet of strata are obliterated. 2he following excerpt from ";tfetamorphic 3eologyn,Leith and £.-:ead* pres-ents a brief but vivid description of the processes involved in 'weathering* and their effect. II molten mass eaters the outer shell of the earth and comes within our range of observaUon.lio sooner does It crystallise than changes begin-with great rapidity nearest the surface.with less t&pidifcy bolov;«?hese cHaeifBS are both physical and c&eaical»?;&fcer .-carbon dioxlde^axygen .and other substances of the hydrosphere m& atmosphere^attacit the rocfcsoiiie ferrous iron of the igneous rocks combines with oxygen and vjator.snd a large part of the iron remains as ilnsonite.Alkalies and alkaline earths for® soluble salts and are leached out In regular determines order® Free quartz is less readily changed or aiasolvea.fhe portions of the bases, which the waters have failed to abatree intend to retain combined with aluaina and silica,taking on water to form nets hydrous silicates.although dom of tfeea may remain in place as carbonates or other salfcs.fho excess of alumina and silic* left after the leaching of the bases from the silic-ates beooffiss hydra ted and forms clay .She re are ultimately- left s then, iron oxide .quarts.clay.awl a variety of hydrous &lusainluffi silicates.character-ised by'a lower ratio of silica to the bases than in the original siH'-oatc minerals.Gride sosios of ore deposits are special cases of these residual products.These sabstsnces on the -erosion surface are Mechanically distrib-ute a and ultimately becosse segregated as soft and sand .or even iron ores. The substances which are ta^en out of solution say rem.in in solution is the sea or may be redepaaited as liraastons,chert.dolcoite Tiron caroonata •or Iron silicate.in other words,as chemical sedlzssats.part of these sub-stances also say b© deposited as cessxjt&.Sha ultlssata result of the des-truction of 'the original igneous rocks .then,ere the sediasnts.ceBsjnts, salts o,f ocean .rive r .late and grotmd waters .and the untransported. resId-lal products of rock decay." II following table,after Mead*, summarises tbe results of weathering. * Redistribution of Elements in Formation of Sedimentary Hooks-_ -yol«Xy „ Bo.3 .Anril-aay 190? r Afofer/<7/ _ - Setf/sTtcnT^ fs/ie/c, -roW-rAw,J - Carr/ecf /si So/uf/or? _ Or/gjrio/ /?ocA< Cerr7e/7f~//?p ATa/er/o/j fe/>? /V/Z/hy ^ o/er/o/s • M/rr Sfc//Vcr/e/- o/ Seo. /Tocfyj /Tej'Wi/c/ Cteyj a/-^JiSM^&s. It is with the "material remaining" division of the above table that this paper will deal. First it would be well to recallin sons detail,the various processes acting upon an exposed rock and their effects. Mechanical Weathering (a) Insolation. Insolation may be defined as the diurnal or other variations of temperature which result ir. exfoliation or surface scaling of rocks* Blackwelder5 s* cornrasnts in this connection are interesting. * Exfoliation as a Phase of Hock Weathering -Jour.Geol. ,Vol.X7jail, — — So.5 .Bov.-Dec. 1925 .no 605-806 , . He says , "Rocks ..especially the felspathic kinds,often weather into concentric shells and round bowlder-like masses.the process is ascribed by nearly all text-book writers to temperature changes,ana especially II ! those from day to night.Other causes which have been suggested are shrinkage on cooling,crystallization of ice or salt in the poros,and katamorphic alteration. It is generally stated that the process is part-| icularly effective in deserts and on high mountain tops*" . . . . . . , , , . . . . . . . . . . . . . . . . . . . . . | "On the contraryvit seems to be a fact that exfoliation develops ' . . best in moist situatSonsd'he process goes on 9aot merely at the surface j ,but at depths of several feet below thick residual soil.Lxperijnents ! indicate that change in temperature,unless it involves high temperatures ,such as those in fires,is powerless to split rocks,although there rem~ ains the possibility that such strains mey be gradually accumulated until rupture occurs.On the other hand,there is convincing evidence that katazsorphi sra(used here to denote chemical decomposition},and particular-ly hydration.is the chief cause of the peripheral expansion which res-ults in the formation of concentric shells." Ehis controversial point may be followed further in ths following papers; lo iiotes on Disintegration of Granite in Egypt - Jour.Geo 1. „i-;o.24 19169pp.382-393, Barton, I) 6 C« 2* as a Weathering Agent- J o u r . G e o l . 3 5 , p p . 1 3 4 - 1 4 0 , iiliot Blackwelder. - 3.Decomposition of Hocks in Brazil -Geol.3oc.of America,3ull.7, 1596,pp.255-214,Branner,Je C e 4.A Study of sons Heating Jests and the Light they throw on .Disintegration of Granlte-.Scon.Geol. fEo.l0,19l5,pp.348-367, . Sarr.'WiA;® • 5.A Treatise on lie tamo rphism -U.S.G.S. ,ilon.47r1904, 6.A Treatise on Sediffientation-T.illiams & \7ilkins,1952,Twenhofel. iMjs)>aa.sj,oa of Water on Freezing Besuiting in oldening of Grog Its and Fissures« She powerful disintegrating effect of frost action upon rocks is II widely recognized.^ater,contained in cracks and interstices,runst,upon freezing,find relief for the consequent increase in volume which occurs. At a temperature of SO deg.F. a pressure of about 138 tons is exerted by the ice forming in a closed cavity.Eelief for this tremendous press-ure is obtained by disrupting the enclosing rock,either by breaking off minute bits or displacement of large masses.With alternate freezing and. thawing,such as accompanies the succession of cold nights and warm daysp the frost work is repeated tine and time again in a single season.This cause of rock disintegration is ,of course,confined to the colder regions of the earth,assuming its greatest importance in the polar regions and in high mountains „although having a by no means negligible effect in temperate regions,Frost work is essentially confined to the surface film of coil or rock in which there can be frequent alternations of temperat-ure above or below the freezing point,and to places where the disintegrat-ed surface material is rapidly removed. Analagous to this nay be the growth of salt crystals of various kinds within the interstices of rocks.Little information seems to be available on this subject,but without question such forces do exist and play an imp-ortant part in mechanical weathering. (c) r.'orls of Organism Many forms of life,both plant and animal,contribute to the destruct-ion of rocks.Lichens cling to rock surfaces,pry off little particles by mechanical means as they-grbw.In a like manner higher plants operate through the forces exerted by their growing roote. ^ 15 ' Animals assist mainly by work -upon the soil,the burrowing animals -the gophe r,wo odehue k , ear t hwor m, ant and others-proving efficient aids to weathering by increasing porosity and by exposing new particles to surface action.Soma of them,like the earthworm,also bring about conniin-;| . ution of the soil by passing it through their intestinal tracts. ij Man has proved to be one of the most powerful organic aids to weat-jrj •••,...' r ,'•••.", " •• •-•• ' -.-»'• '••••• • • ; .- • ' ' . ;J he ring, but his work is only recent and in general may he neglected. ; I .• . v • ...•-•'... *fcUl Other Mechanical Agents 1 Wind plays a not unimportant role in weathering.lt acts as a pow-erful abrasive oa exposed surfaces,using as a tool transported dust and sand,as well as tearing away any material which has been sufficiently loosened by frost or chemical action. In a like manner rainfall may help in the comminution of a rock through direct impact,especially if the surface be tried by other agencies. • Chemical Weathering • Mechanical agencies tend to separate the particles of a rock and to furnish fresh surfaces to chemical attack,aqueous decomposition being the most important,depending for its efficiency partly on the water itself and partly on dissolved acids,salts,and gases. Bain water,carrying in solution oxygen,carbon dioside „and other substances in varying proportions,falls upon the surface of a rock and sinks more or less deeply into its pores and crevices.Water and gas both exert a solvent action,and the fluid which then saturates the rock bec-omes charged with the products of solution.These may intensify or inhibit II further action depending upon circumstances®Some of the dissolved matter 9redeposited9may form a protective film and so delay or prevent further solutionoThis retardation is accompanied oy a rubbing of the loosened particles together,and so the coating of insoluble matter is removed. (alOomposition of the Atmosphere Atmospheric air consists normally of a mechanical mixture of free nitrogen and oxygen in the proportion of 4 volunes of ths former to 1 volume of the latter.In addition are small and comparatively insignifi-cant arsounts of various combined gases and salts,of which carbonic acid is by far the most abundant.Still snailer quantities of aramoniacal vap-ors exist,and in volcanic regions there have boen detected appreciable amounts of sulfuric acid. Varying proportions of these gases are dissolved by rainwater in ite passage through the atmospheretand it is in aqueous solution that these components becomo effective agents for decomposition. '(.l)'3S-itrogsn>Ei.trlc A.old»apd Ammonia Hitrogen itself is believed to be wholly inoperative in promot-ing rock decomposition,but there is less certainty with regard to ths efficacy of nitric acid and ammonia.These are knov/n to form a part of the atmosphere,in most cases ammonia being in excess over nitric acid ,ivith the reverse being apparently true in the tropics. Usually,hov/ever, the percentage of ammonia equals or exceeds the amount necessary to combine with the acid,and ammonium nitrate results,leaving little , i f any acid available for rock ^e a t he r I k g. Then again the amount of nitrog-en in the soil Is usually f£r too small to supply the demands of grow-ing plants,and in all likelihood a large proportion of that which finds II its way tliers is immediately taken up by these organisms. ' ..(.glOarbomic Ac id The amount of carbonic acid in the air is a fairly constant quantity under natural conditions,increasing in the vicinity of large cities and decreasing in the country. Carbonic acid in aqueous solution provides one of the most active agents for the chemical decomposition of rocks. (5 ] Oxygen Normally o:cygen is the most active principle in atmospheric air .and to it is due the process of oxidation which almost universally characterizes the decomposition of silicates and other minerals cont-aining iron in the protoxide state.lt is almost inactive ,however, unless aided by the presence of water. 14} Other Components Hydrochloric,sulfurous,and sulfuric acids are present in such min-ute quantities that their action is not of widespread importance Never-theless in restricted areas,for instance in the vicinity of active vol-canoes, they imy play an important part in weathering. ••(b.) Solubility of Minerals •experiment has shown that practically all minerals .especially the rock-forming ones,are soluble in water and carbonic acid.Under usual con-ditions the following order of decomposition obtains:pyroxenes and arnphi-boles most easily attacked,followed by plagioclase felspar,then ortho-clase and the raicas,with muscovito the most resistant of all.Even quartz is not quite insoluble.and the corrosion of q u a r t s pebbles in conglomer-! 'I • . * | . . j • 1 8 |4 v •H • . •' ." • •••:•• ; ] ates has been noted by several observers.Among the commoner accessories | apatite ana pyrite arc most easily decomposed.magnetite Is less attacked j • . - • . -,and such minerals as zircon,c orundu®,chromi te ,ilaeni te ,e tc.tend to acc-umulate in the gansy rock residues.ii.ven those last are not absolutely ; | incorrodi ble ,corundum, for ins tance, slowly undergoing hydration * be ing 11 .-.'•.'.• • • ij converted at least superficially,into gibbsite or diaspore. |! Clarke1"in speaking of the experimental decomposition of aluminous I • • f - -  • -. , , IL lt ; | mIL .•* ~ ' - .- , , • , • - • - ' . j *JBfe&& ..of.. Jteochsmiatry-g.S.&«S. Ball. 770.1924.o483- Clarke.Q-.'tV. ~ f-j silicates9makes the following comments: ! j • • • • • ' • . • . - • " • • • . -• | "When orthoclase Is shaken tip with water an imissdiate extraction of I alkaline salts takes place,but it is only a partial measure of the amount of decomposition.Colloidal substances,silica or aluminous silicates,are formed at the same time,which retain a portion of the separated a l k a l i 3 * ~ * j but give it up to electrolytic solvents.'' "These gains do not imply increased decomposition,but only a liberat-ion of the soluble compounds which had been entangled in the colloids that were formed at the same tine.Any salt In solution is likely to affect in soma such manner the apparent solubility of a rock or mineral,a con-clusion which is in harmony with many observations upon the tendency of soils and clays to absorb salts ,and especially salts of potassium from percolating waters,is the latter change in co,position,their decomposing and dissolving capacities are altered;and since the rocks differ in comp-osition,no general rule can be laid down to determine what ths effects of water in any particular case will be . " In connection with the- corrosion of quarts- pebbles In conglomerates, mentioned above,two Interesting papers have been presented.The first by II by Fuller*,mentions the occurrence of etched and corroded quartz pebbles - itching of Quarts in the Interior of Conglomerates-Jour. Geol.,1902 l— •Vol.a .p.615 .Fuller in a confloraerate„in which a.3 much as nine-tenths of the pebble has been remove deleaving a strongly pitted and rough surface .while the part embedd-ed in the matrix is satooth..3e notes that the etching is confined to bed-ding planes,or to the vicinity of vegetable remains,and suggests that al-though felspathic grains might,on weathering,afford sufficiently strong-allcaline solutions to otch quartz5aany instances arecrocorded where this has not occurred,and it is likely that the corrosive solutions were der-ived from the vegetable matter of the rock itself. In tho second paper Hayes*points out that all recorded. cases where Solution of Silica under Atmospheric Conditions JlaLlj^eo^Soc^_of . America, V o l . 8 . 6 . 1 8 9 7 .p.SiS,Haves there has been active solution of quarts,occur in a heavily forested reg-ion where there is an abundant layer of humus.There would therefore app-ear to be present an abundant supply of humic acids which are intermediate products in the decay of vegetable natter,While simple humic acids are relatively inert,they readily absorb nitrogen from the air,being converted into azo-hundc acids.,nitrogon not being present as ammonium,although the anraofaiua is fonsed on further oxidation.These acids have a strong affinity for silica,forming a new series in which the amount of silica is apparent-ly proportional to the amount of nitrogen. T.hs compounds thus formed are easily.soluble in alkaline carbonates,forming alkali salts of silico-aso-huaic acids.Alkaline carbonates must also be abundant.The action seems to be furthered when the auartz is covered with lichen. II 25errill* attributes th«> corrosion of quartz to alkaline carbonates gen-* Bocks.Rock-Sea thsring,and Foils-Macraillan ,1921 ,p.252 -Iferrill.a.p, erated -luring the decomposition of soils. For further references on this subject the following publications may be consult-eds (1) American Journal of Science ,4th.series„vol. 19,1905,p.28£ -O.H.Sn^th (2} Solubility of Quartz in solutions of Boras or Alkaline Silicates- Jour.0hem.Soc.,vol.789pt.2,19a0,p.595-G.Spezia {3} Solubility of Gelatinous Silica -Jbur.Aiaer *0henuSoc*,vol.39,1917,p.2630 -V.Lenker and H.3.aerril (c . ) Decogmos.ltiQn of Silicates. The minerals of rocks,such as felspars,T3ica»araphibole,or pyroxene^are not dissolved in water but decomposed by it,the carbon dioxide which is nearly always contained by,,the water,acting as a powerful aidUAccordlng to modern viewa,dcc ompcs i t i on is the result of hydrolysis,the -partly ionized water acting as a stronger acid on the weaker silicis one,and the carbonic acid acting or. the bases set free.The carbonic acid in this way does not react directly as a solvent itself,but by combining vith tiie released bases,tend.?, to prevent equilibrium from being .established, thus Intensifying the reaction. She deco.upcsition of felspar Is exemplified by the following equat-ions: iuilSi3o8 pi as HOH KCH plus HA1S1308 2K0ii plus 2BAlSig0g — E 4 Al 2 £i g 0 9 plus 4S102 plus X2CO3 II lBff In general the silicates « ,st easily decomposed, are those contain protoxides of lima,or manganese,and iron,and the first indication of their decomposition is signalled by a ferruginous discoloration and the appearance of calolte.Ia a ,oist or perhaps any climate,minerals consisting essentially of silicates of alumna and ,agnesia are less liable to decomposition than those containing considerable proportions of iron protoxides or lime. The actual order in which the various numerals tend to be broken up is not tod.tat appears to depend on several factors- ,auch as associlf ion.cli.nate .etc.Serrill* makes the following observations: ^as^sas^ra^thgring .and -; ^ " ' ; n o i "rr;—-7;—-—-—— ^ 1 .-Lterrill.a.p, '-wans, ooserved that the decomposition of the granitic rocks of the Chilean coast Resulted in the felspars yielding first,becoming ,hite and opaque and of a friable,earthy appearance.But it should be .noted that thi£ change may not have been a purely physical one,and due to splitting up of the felspars along cleavage lines.Fournel,from a study of the process-es of kaolini a a ti on ,was lead to state that hornblende yields l e s c r e a d -ily to dfccomposing forces than does felspar,when the two are associated in the same rock. Becker .hoover , ins tudying deep-seated decomposition in the Gomstock lode of Nevada arrived at precisely an opposite conclusion-the felspars as a whole offering .ore resistance than augitehornblende, or mica.Lindgren noted that the decomposition of the California grano-diorite manifested two distinct phases^he first due to the decomposit-ion of the felspar grains alone resulted in reducing the rock to a soft crumbling mass.In the second stage,the biotite and hornblende are also decomposed,the biotite being the most refractory." II Eies°observes that mgnesi upbearing micas are more soluble than rauscovite,and albite more so than orthoclase. -'Clays ,Occurrence,Properties ean& uses -John Wiley and Sons, 192? — - — — — — . — — — : — : • 11 ., .:.,••.••. H.lxles lindgren* places the femies as being the most easily attacked.givins .1928.nT5i2 - W.Jiindgren" ' rise to an abundance of calcium and magnesium salts in surface waters, soda-lime- felspars cose nest,with albite and orthoclase the most resist-ant* In generate silica appears to be lost relative to alumina,iron remains nearly as constant, as alumina,but may act in a more variable manner. Magnesia is usually lost to a slightly greater degree than silica,but is rather variable.Lino is lost to a greater fegree than magnesia,due to the retention i B GOrne of the comparatively stable Hydrous magnesium sil-icates. Soda shows a smaller loss than lirao but possibly greater than magnesiurn.Potassiurn is retained relative to boda and lire m c h the same as is magnesium,(retained in the relatively stable minerals orthoclase and sericite).Water is increased in amount in every case. Of course there are exceptions to the above order,a case in point being exhibited by the decomposed diabases of Sao Paulo,Brazil* in whirl a aerro iioxa in Sao Paula,Brazil -Scon.Geo 1.Vo 1 . X X I X , E o . 3 1 9 S 4 —— . P.6SQ„ A.Preiss caleiua is retained relative to sodium. Undoubtedly potash and to some extent magnesia owe their retention not only to the formation of secondary minerals,as sericite,which are relatively stable under surface conditions,but to the formation of coll-oidal matter which has a high adsorbtive power for these substances. • - :• 23 lot ail the substances removed in solution find their way to the seaQ A large proportion of them are deposited v;hen a new Condition,such as evaporation or the action of bacilli , is encountered® Id . ) 'OoHolds. Colloid phenomena prevail in the surface sons and play such an imp-ortant part in the processes of weathering that a br&ef review of tte prop-erties of colloidal solutions and colloids in general might not be out of place® In general colloid processes take place b^ preference at the contact of air and land or of water and land;in other words,at the bottom of rivers ,lakes0and seas,in the uppermost layer of rocks,at the surface of soils and at short distances below the surface in the zone of oxidation* Fir&fe there is no separate class of substances called colloids.Given the proper conditions(which vary) all substances may be prepared in the coll-oidal state*which is intermediate between true solutions ,on the one hand, and coarse suspensions,on the other.In sons cases these are almost con-tinuous transitional stages from end to the other of the system. Colloidal solutions consist of two phases,andare therefore heterogeneous as contrasted with rttrus" or molecular solutions,which are homogeneous. The essential and distinguishing properties of 'sols' (colloidal solutions) ares (1) Heterogeneity,and (2) Very large surface of contact. Of the two phases present in colloidal solutions9that which plays the part of' solvent* is known as the dispersion medium, or external, or cont-inuous phase,whilst that which corresponds to the solute is tho dispersed or internal or discontinuous phase. II Das to tho large surface of contact that exists in solssurface ton- _ slon -teeofi©6 of great is^rt&iic8*23iQ exy&eat of surface of ,the -disperse phase is usually ro f erred L& -as its specific surf ace,which is the surface per unit volume* Colloidal solutions are much 120re prone to Changs of a physical nature than are true solutions,the change, vdie the r it be accompanied by a settling out of the disperse.phase or hot8is nearly always froa a higher to a low-er state of dlsparsiOBol'he disperse phese,if precipitated,may take the form of a granular sediment,or it may appear as a jelly-like mass retain-ing a considerable anoant of the dispersion m&ltm.,sni is then called a gel.Intermediate bafeeen those two are the so-called gelatinous precipit-ates® ' " iilectrolytes have the greatest infl-asr.ee on eols9but the latter behave amongst themselves differently towards different electrolytes. Colloidal solutions are divided into: -(IjSuspsnsoids-in those the particles of the disperse phase are believed to be sol id examples of inorganic suspensoids arc the actal sols, sulfide sols,silver halides,and many salts. lEjflraalsoids-' in these tho particles of tho disperse phasu are believed to be liquid.iizaisples of inorganic emolaoids are silicic acid,tungstlc acid9ani the hydratos of i r 0 s e al u;ui n i urn, and chromium* Generally speaking the factors that tend to maintain uniform concent-ration of tho disperse particles of dois aro osmotic pressure and elect-rical repulsion .whilst surface tension acts in tat opposite direction* Equilibrium results when these two tendencies are eoual* II SjS Emulsoids The vlsoosity of emulsoids is high,their osmotic pressure and rat of diffusion extremely lowland their surface tension Is much less than that of the p >re dispersion medium. In coagulation,emulsoids usually set to a Jelly-like m s s called a gelowith organic substances usually the coagulation of an emulsoid is a reversible process5whl1st the inorganic ones are irreversible, iuetailic Hydroxide Sols These are into radiate between suspensoids and emulsoids .A distmc tive feature of this class of sols is that the disperse phase is positiv ely charged against rater.They are susceptible to the influence of elect rolytes.the coagulum in some cases being granular and in others a gel. Metallic hydroxide sols may be prepared by a variety of condensation net-hodssthe most interesting of which from the geological standpoint is hyd-rolysis.. ••. •• fiels The most stable gels are relatively dilute and are prepared by slow precipitation of dilute colloids or on mixing of dilute solutions where the degree of supersaturution is only small. Silica Gel - She coagulation of silica sol is irreversible and Is accompanied by a change from a clear 11quid,through an opalescent stage to a translucent coherent mass.'.71 til gels containing 5% of silica or more visible separation of water occurs and the gel shrinks.fepose* to the air the gel apparently dries and forms a transparent glass with a hardness of 4 . 5 to5.5 and' still containing macn water.On careful drying it loses 90% of its volume,and although so far no sign of'crystal-II line so * r a . W . ^ 4 ^ . u r t . t K l d s t 0 a p p s a r in tilt, dried or ignited material* :;iaorals isxhiMting Colloidal be&avlour AltUougH a colloidal precipitat, I I B , t l l U i a U y ^ # corresponding to a certain stoichiometric f o r . l a , t i ! e to acLsorbt-i 0 n 6 0 0 , 1 C h M S B l M s ^ « • » » « « * * « « in various ana irreg ular proportionsv80 that tae final prodm-a 3 e l , f „ r o . a . p l e - , ^ te . ^ fore of several gels .apparently entirely aon^neoussor it „ contain solutions of oleotrolytesjor T,-hon hardened.it 5 a , „ . w (jcs y mixture 02 a gel and minute crystallized particles. It follows from this that a.hardened colloid gel does not necessarily have a definite chemical composition and therefore,does not f . l f i l t h e common r e p r e s e n t of a 'mineral*.nevertheless the a p p r o v e composition is the same for each typs of colloid 'mineral', Mineral g o l s do not remain indefinitely in this «„».* » 1,. u i j ^ o n a x T e m p e r a t u r e or time9or both,induce a crystalline structure. Cliachite U 1 2 0 S . ( W and Limonite ( F e . C ^ O . (H 2 0) x , are examples of colloidal minerals.fhe former c o m p l y possesses the composition A1 2C 3 .2H 20 andthe latter ^ Q ^ Q . a l t h o u g h wide variations in the water content is found in both rninerals.HalloysiteiAl.O^^SiO^ . n ^ O ) is , n example of a mineral,originally colloidal,but usually found , ith a tendency to micro-crystalline structure and slight a n i s o t r o p i c type of min~ eral is termed a matacolloidc SHe following works were referred to in the preparation of this brief resume of colloid phenomena: U ) ®he Colloid Matter of Olay and Its Seasureaent- U.s .Q .8 . Bull.588 %-Ashley 2? 9 {2} Physical Chemistry for Colleges—McGraw-Hill ,1926,pp.397-426 Millard (3) She Theory and Application of Colloid Behaviour - McGraw-Hill 1324-Ghap« XVIII -Lindgren (4) The Bole of Colloidal Solutions in the-' Formation of Mineral deposits -Trans.Inst.TUn. Met..Dec.1924.-Bovdell (5) ihe Chemistry of Colloids- John wlley and Sons ,1917-Ssigrnondy (6) The Hole Of Hydrolysis in Geological Ohemistrv -iscon.Geol. »vol.6,1911 -Wells Precipitation of Colloids Electrostatic charges are assumed by particles suspended in a liquid ,a substance having a higher dielectric constant thhnathe liquid assumes a positive, chargepa substance with a lower one assumes a negative charge. As a result of these charges,suspended particles^whose masses are small enough are equally distributed through the liquid,and prevented from coal-escing by mutual repulsion.The static** charges which ions of electrol-ytes carry neutralize statical charges of opposite sign on colloidal particIds»Hydrosol conditions are only possible if one of the reacting ions remains up to a certain minimum amount in excess5on exceeding this limit gel formation begins„ Some of the simpler colloids,for example noble metals probably do not form gels at all ; their precipitation is always an irreversible one to set gels.Substances that form gels have a tendency to form crystals,and especially complect forms., when a very stable sol,in the presence of a less stable sol of the saira sign,is acted upo# by an electrolyte that would, not preceipitate the for-mer, but would precipitate the latter alone,the influence of the former is often sufficient to protect the latter. II Colloids of opposite sign will perform the same function In precip-itation as electrolytes. Solution,Transportation,and precipitation of Iron and Silica Shen silicates are decomposed ,silica is invariably set free, as illustrated by the formula for the decomposition of orthoclase by pure water: K 2 0 .Al 2 0 3 . 6S i0 2 plus 2H6H - 2K0H plus 2HAlSis0e I f the hydrogen ion concentration is favourable,the unstable comp-ound M l S i 3 o 6 will break up to form kaolinite and silicas % 0 plus 2HAlSi30Q - Al 2 0 3 . 2S i0 2 . 2H 2 0 plus 4Si0 2 The released silica will go into solution as a colloid.If the hyd-rogen ion concentration is incorrect,hydrous aluminium oxide may result .sone of which is likely to be in the colloidal state. Jioore and Maynard* carried on extensive research in the field of solution,transportation,and precipitation of iron and silica and soma of their findings should prove of active interest here. oolution,Transportation,and Precipitation of Iron S i H ^ -tipore and M s . ^ . ^ (1) Organic matter was found to play an important part in the trans-ortation andsolution of bog iron ores, the proportion carried being dep-^t on the amount of organic matter in solution.The amount of lime a,aaid bicarbonate radicle do not materially affect the proport-carried,indicating that the iron is carried as salts of r as a ferric oxide hydrosol.stabilized by organic coll-29' (2) Carbonated water proved to be an effective solvent of iron and silica from siderite,magnetite.olivine,and gabbro.Pure water dis-solves silica to the extent of one part in ten tbousa,d9the solubil i t y being increased by the presence of oxygen,carbon dioxide,nitric acid . - m i l quantities of sulfuric acid,and especially h u ^ s acids.Silica can be dissolved in appreciable quantity by cold carbonated water from hornblende,actinolite,ePidote,serpentine,felspar,adularia,olivine,wol-lastoniteMuscovite,asbestos,talc,quart, ,and dioPtase. In this connection it is interesting to note that Lovering*states ^ ^ ^ that xiagsesiiun and calciu , bicarbonate are effective solvents of quart, ,jasper and taconite,and that sodium hydroxide is a niost effective sol-vent of opal and chalcedony,andhas an appreciable effect on quarts,Jas-per,taconite.greenalite ,actinolite ,and glauconite. Clarke* mentions a brownish solution,colloidal in nature and poss-essing feebly acidic properties which be e x a c t e d f r o , decaying "Plants,andis reputed to be a powerful agent in the solution of rocks. He believes however that its disintegrating power is really due to carb-onic acid resulting from oxidation of organic matter. I - ^ ^ e o c j ^ t r y - U . S . G . S ^ i . 7 7 0 . 1 9 2 * . P l M l I i r ^ : v , - n i » , i ~ Weiss* has shown that peat solutions can change an impure clay to a residue of alaost pure kaolinite. I _Zeit . Prakt. genl. , 1 9 m ..eiss are Gruner'remarks that solutions from decaying organic matter among the most effective solvents of all oxides and carbonates of iron ,as well as most of the silicates. J£CQS'geola_,Ko.i7.1922 -Tm.AZ2.-A?,f> -a™™r 30. (3) 'Iron is not carried as a bicarbonate in natural surface wat-ers high in organic matter,but is likely transported as a ferric oxide hydro301 stabilized by organic colloida.' (4} {A relatively small proportion m y be carried as sMts of org-anic acids or adsorbed by organic colloids.• (5) 'As much as thirty-six parts of ferric oxide can be heldnin colloidal solution by sixteen parts per million of organic matter.* (6) 'Under exceptional conditions iron might be in solution in surface waters as slats of inorganic acids and as a ferrous silicate hydrosol.' • (7 ) 'Silica is transported in natural waters as a colloid and not as acid ions,if the concentration does not exceed twenty-five parts per millionsabove this some alkaline silicate may be present.' .(8) ' All iron carried to the ocean is precipitated immediately by the electrolytes of the ocean,if the iron is in colloidal form. Bacteria also precipitate ferric ammonium tartrate as ferric oxide.' (9) ' In EaSiOg solutions with a concentration of thirty parts per million silica,calcium bicarbonate and sea water are two of the best precipitants of colloidal silica.KaCl and K 2S0 4 are less powerful. % S 0 4 gives practically no precipi&ate,unless the consentration be raised to five hundred parts per million,when a heavy v.hite precipitate results.® Shorpe^found that aqueous solutions of aluminium chloride and sod-ium silicate react to form a precipitate of the composition 2Al 20 3 .3Si0 2 ,which adsorbs silica,andin the presence of silicic acid is converted int into the compound Al203 .2S102 ,analagous to kaolinite. II JJigMflnagy. of Arrolied Chetaistry.Vol.7i -53 .morns V a n H i s e a n i L e i t h C found that ferrous sulfate reacts directly with solutions of silicates of alkalis,giving a granular precipitate of the formula Fe0.2Si0o l2^jfLili*_,Jipno.52 -p.521- fan Hiss Leith The above observations point out the possibility of obtaining silicates by reactions between different salts and sodium silicate .provided that the solutions are of such concentration that complete hydrolysis has not taken place.Solutions of sodium silicates are hydro-lytically decomposed into EaOH and colloidal silicic acid, ' It is generally conceded that complete hydrolysis of silicates takes place at a dilution of 2543 parts per mi 11 ion.Consequently at dictions such as exist in nature .complete hydrolysis has occurred and silica is almost all present in colloidal fornuExperinsants shoi- that the lower the concentration of a silica hydrosol.the greater the length of tin© required for its coagulation. ' When silica and iron are carried together in nature,a stabilizer is required,peat solution being the most e f f e c t i v e l y by adding an electrolyte ferric oxide is thrown down and silica remains nearly int-act. ' Composition of the Soil Colloid The composition of the soil colloid,as compared with the whole soil,is higher in alumina,magnesia,phosphorous pentoxide.and sulfur, and lower in silioa.i'he deficiency in silica is believed to be dps to the ageing process to which all soil is subjected,in which there is a tendency for silica to be transformed to secondary quartz. IVeiser * considers the soil colloid to comprise varying amounts * The Hydrous Oxides - IcSraw-Hill .1926.n.34- Welser :of. Eydrous oxides of iron,aluminium,and silicon with varying amounts of adsorbed salts.She so-called alumino-silicates are for the most part adsorption complexes of indefinite composition formsd by mutual precip-itation of negatively charged hydrous silica and positively charged hydrous alumina.Organic material and hydrous silica act as stabilizers. Under aerobic conditions organic matter is oxidized giving water.carbon dioxide and other salts.Under anaerobic conditions,however,a colloidal substance known as humlc acid or humus is formed,which resists,after its formation.decomposition under aerobic conditions. (e.) Weathering Processes (1) Oxidation Oxidation is perceptibly manifested only In rocks carrying iron either as sulfide.protoxide.carbonate or silicate.Iron is the most important inorganic compound oxidized:iron is altered to hematite and magnetite when present as a sulfide,or if alteration is accompanied by hydration,to limonite,goethite and turgite.At the sane tiipe sulf-acids are formed,which in the presence of alumina and alkalis give alum and gypsum,or other sulfates,which being soluble,are usually removed.Hydrated oxides.sulfuretted hydrogen,and perhaps free sulfur,may be formed as well.Such an oxidation is attended by an increase in bulk,so that if nothing escapes by solution,there may be brought to bear a physical agency to aid in disintegration.Pyrites is ,in general,a less conspicuous agent in promoting rock decomposition than the protoxide carbonates II and silicates.In these the iron also passes over to the hydrated ses~ quioxide stateSas first indicated by the general discoloration.The most eoffiffion minerals thus attacked are the ferruginous carbonates of lira© and magnesia,and silicates of the mica,pyroxene and amphibole groups.As the oxidation progresses,the minerals become gradually decomp-osed and fall away into unrecognisable forms.The red and yellow color " of soils are thus due to the iron oxides contained by them. In so as cas-es, the mineral magnetite „g mixture of prot- and sesqui-oxides,undergoes further oxidation and also loses its individuality. Deoxidation is a less coittson feature than oxidation.Organic acids ,inaqueous solution,may take away a portion of the combined oxygen of a sesquioxide.converting it back to the protoxide state.Through the same process ferrous sulfates may be converted into sulfides. The oxidation of organic material results in the formation of acids of the huaiic group,the Host common bsing humic and crenic acids.By fur-ther action these are broken down,ultimately forming carbon dioxide, water,amnionia,and various nitrite and nitrates.Aerobic bacteria are the most active agents in bringing about this action.In tropical regions where bacteria are more active,the production of nitrates in the soil is very large,although the greater portion of these nitrates are carried - away. ..• (2) OaEkanaMfilk. The process of carbonation consists mainly in the substitution of carbonic for silicic acid in silicates.As was mentioned esrlaer in this chapter,modern opinion emphasises hydrolysis by water as preceding the formation of carbonates.The work of many experimenters,including II that of iaoore and ilaynard.qnoted previously,shows that carbon dioxide in ayueous solution is a vastly more active reagent upon silicates than p m water alone .An equation illustrating the typical decomposit-ion effected by carbonic acid solution follows: 2(CaO.AlgOg.2SiOgj plus KgO.A12Oj.6S102 plus 2CC2 plus 2il20 — % 0 . 3 A l 2 0 3 , 6 S i 0 £ plus 2GaG03 plus 4 Si0 2 If the hydrogen ion concentration is correct: X 2 0 e Al 2 0 3 . SSi0 2 plus H 20 — Al 2 C 3 . 2Si0 2 . 2H 2 0 plus 4Si0 2 or under different conditions; Al 2CW.6Si0 2 .H 20 plus A l 2 0 3 . 2 S i 0 2 . H 2 0 - 2Al 2 0 3 . 6Si0 2 . 2H 2 0 <.•••'•.',.••-•• and ' - • . . . ' . . • . • . • 3 t o S 0 B ^ 8 i 0 8 . % 0 ) plus 6K0H p l „ 2C0£ ~ ^ O . W ^ S ^ . ^ O plus2K2C03 plus 6Si02 plus 4H20 As illustrated.above SaoUnite instead of Muscovite may well result from the same combination.Considerable hydrated aluminous oxide may also result from the same r e a c t i o n . ^ resulting products seem to depend upon the hydrogen ion concentration of the solutions,a ph value of 3 . 8 at 20 deg. or of 4 . 2 at 70 deg.C. in an aqueous solution saturat-ed.with carbon dioxide appearing* to favour the formation of kaolinite, especially with decreas of acidity. Carbonates of alkalis and a i r l i n e earths thus formed,are removed in solution,and become potent agencies for further desilication. £ven though hydrolysis is the primary action in the decomposition of silicates,it is an incontrovertible fact that the presence of carbon ; 35 dioxide in solution,increases the action very greatly.The explanation forn this undoubtedly lies in the combination of carbon dioxide with the hydroxides of alkalis and alkaline earths,thus Iceeping the ph value such that further hydrolysis will continue. ' •—(5-) 'Hydration- • • • . . . • Hydration commonly accompanies oxidation,and is in fact an al-most constant accompaniment of rock decomposition^ may be observed by comparing the total percentages of water in fresh and decomposed rocks as given by analyses.The process consists of the replacement of anhydrous silicates and oxides by hydrated members of tho kaolinite, serpentine,talc,chlorite and zeolite groups among the silicates,and gibbsite,diaspore,cliachite,and msmbers,of the limonite family among the oxides,and hydrated calcium sulfate(gypsum) anong the sulfates. She reaction of hydration involves an expansion of volume and a liberation of energy. Merrill* has calculated that the transition of a granite into an arable soil , i f no material is lost,must be attended by an increase in . bulk of B8%-« - J o c k s ^ o c k g e M h e i l n g and Soils - Uacmillan 1921.n.166 -G.P.aarril 1 It would therefore appear that hydration plays a not unimport-ant role in the actual mechanical disintegration as well as the decomp-osition of rocks. Johnstone* has shown that normal muscovite.when submitted to the action of pure and carbonated water for the space of a year,underwent very little change other than hydration,and a diminution in hardness II ,lustre,and elasticity,, it appeared to be merely converted into hydromuseovite,the hydration in pure water having gone on nearly as fast as in that which was carbonated.Biotite when similarly treated ,showed a slight discoloration or bleaching on the edges,accompanied also by hydration,and when carbonated water was used,a distinct loss in iron and magnesia,through solution. • t e ^ J g n ^ o l .-Soc. L o n j o i r r i i i ^ ^ tone A brief review of some of ths more important hydrous oxides and silicates produced by hydration follows. Hydrous Oaririfts of Iron Of all the hydrous oxides of iron,the monohydrate goethite or lepidocrocite,alone possesses a definite crystal form.r,hen found in an indefinite amorphous condition,with an excess of adsorbed water, the mixture is known as limonite. Dorsey* nations the following definite hydrates of ferric iron and attributes to each the characteristics of a definite mineral sPe-ciess Limonite — 2Fe 20 3 ,SH 20 - yellow brown Xanthosiderite - Fe 20 3 .2H 20 - Golden yellow to brown •Goethite - Fe 2 0 3 .H 2 0 -yellow,brown,brownish-black Surglte — 2Fe 20 3 .H 20 - red to reddish brown Hematite — BfegOg— red " Origin and color of Bed Beds -Jour.Geol. ,Vol.XXXIF,K o .2,^b-ilar, -— 1'' '"'' -j, ",',, , _ la26 —Sorsey • • • • • Shis subdivision of the hydrous iron oxides into a series of specific minerals Is in common use,but it would appear more likely that apart from the mono-hydrate ,goethite,these so-called minerals II merely represent ferric iron,in the colloidal forthwith vasying amounts of adsorbed water® Weiser" points that since but one precipitated hydrate of ferric * nv She Hydrous Oxides Sraw-3i 11.1926 —Weiser oxide has been proved to exist,it seems improbable that red colloidal solutions contain definite hydrates.The differences in hydrat&dn of fer-ric oxide sols are due to differences in specific surfaces. In experimental work,colloidal ferric oxides can be prepared fairly free from electrolytes,but some electrolyte is required in such sols to ensure their stability.Any number of hydrous ferric oxides are possible,differing among themselves in sise of particles,and hence in the amount of salt or ion adsorbtion.A substance always shows a strong tendency to adsorb its own ions,andin this case the H ion is strongly adsorbed,while the 01 ion is ranch less so.The result of this preferent-ial adsorbtion is a stable positive colloid.Adsorbed ions will not show in chemical tests,but there is an equilibrium between adsorbed ions and free ions; in a dialyzed solution the sols tend to lose ions and become less stable. Apparently coagulation by eleotrolytes is not accompanied by the growth of primary colloidal particles,the latter merely agglomerating into loose clumps without change of specific surface. Anhydrous heaatite is black when crystalline and red when pow-dered, turgite is deep brown,limonite from light brown to yellow,and limnite full yellow.Just as the variations in color of the anhydrous oxides seem to be due to the size of particles present,so the color of hydrous material changes with the size of its particles.The finely div-ided brown particles are changed by heating into larger yellow or still larger red particles. Tvhen a very dilute solution of FeCl,, is prepared it is color-less at first but changes spontaneously to yellow,then to reddish-brown.Yellow particles,free from the brown,are not transformed into red by heating,but the brown are.Yellow likely represents the hydr-ous mono '•hydrate® The color of hydrous oxides of iron,then,is seemingly depen-dent on the size of particles composing the sol or gel.The dependence of color upon particle size rhfcum, is a.function of the water adsorbed ,which varies directly as the specific surface of particles and inversely as the size of particles themselves. It would therefore appear that there is but one definite hydrate of a fixed, compos it ion, the mono-hydrate goethite- or lepidocrocite 5and that limonite is a colloidal gel .differing only from xanthosiderite,and turgite in the size of particles and consequently in the amount of ad-sorbed water® Dorsey* observes that ferric hydrate will lose water and eventually turn red by itself i f given enough tine.Bydrated iron is not a stable body and even if continuously submerged will lose water as long as it is not in molecular combination with other oxides.Where it is bound up with other oxides,such as silica.dehydration may be interrupted.Elevat-ion of temperature speeds up the reaction,but the primaty requisite to natural dehydration is that of time. Origin and Color of Bed Beds —Jour.Geol. . T o l . X O T I . Ifo. 2 „ Feb-Mar p V B a p AVU 9 UK3 ij —iiiStl8 1926 „Dorsey Shis dehydration of ferric oxide .according to Barrellfis not wholly dependent upon heat and pressure,but is,to a large degree.spontaneous. * Climate and Terrestial Deposits - Jour.Geol..Vol.XVI.Ko.S, April-May .1908»p.296 -Barrell Is general true hydration is an exothermic reaction requiring the application of external energy for the removal of water of hydration® Shis does not appear to be strictly the case with the hydrous oxides of iron.Although heat and pressure expedite dehydration,they are not essential,and given time enough the process will take place spontan-eously. It would appear that,neglecting the comparatively stable cryst-alline mono-hydrate,there is a tendency for the colloid particles to •grow of their own accord,with a consequent reduction of specific sur-face and loss of water.until the anhydrous ferric oxide is reached.On the other hand,as Hieappoints out,the dehydrated oxides are capable of rehydration even in a room. * Clays,Occurrences,Properties,and Uses - John ¥iley and Sons,1327 . - -Bi'es -It therefore appears that the many names ascribed to the hydrous oxides of iron because of certain indefinite physical differences ass-ociated with plausible but not well established chemical formulae are unmerited on a strictly scientific basis. Hydrous Aluminium Oxides Earlier papers described such oxides as A1„0*.H20,corresponding to the crystalline mineral diaspore;Al203.2H20,corresponding to amor-phous * bauxite'; and Al^Qg^SHgO,corresponding to crystalline gibbsite. Bumbold* describes these three minerals,but adds that many authors consider that bauxite is not a mineral ,but a hardened and in part crys tallized hydrogel of indefinite composition.In passing he also mentions that diaspore is indigenous, to deposits formed at higher temperatures - 40 than those prevailing in residual deposits, * t ute. 19257^10~ In this connection it may be mentioned that the term 'bauxite' is now generally used to describe residual deposits in which hydrous aluminium oxide is present in sufficient quantity to afford a commercial, ore of aluminium.The term has no longer any mineralogic significance.being replaced by 'cliachite'« Holland* states that the tendency is for dehydration of gibbsite (A1 2 0 S . 3H 2 C) to diaspore (A1 2 0 S . H 2 0J to occur naturally. * On the Constitution.Origin.and Dehydration of Laterite-Seol.Mag.,1903 — • P.-63 .-Holland The above statensnt although interesting appears to be just the contrary of what actually occurs,as will be pointed out later. Morse* defines three definite hydrates,diaspore(mono-hydrate)p a dl-hydrate,and gibbsite or hydrargillite(tri-hydrate). I J i j s s i ^ s i P E i ^ S t a ^ -3tal 1.l'JTl9*H3 - linrse -tTTI Weiser* .however,says that the existence of definite hydrates in gelatinous alumina has been rendered doubtful by the work of several experi-menters,who have shown that,at constant temperature,the precipitated oxide takes up or gives off water until the vapor tension of the substance is the same as that of its surroundings,the vapor pressure of the hydrous oxide being also affected by the conditions of its precipitation.The only definite hydrate,formed in this manner,appeara to be the trihydrate,gibbsite.Unlike the fresh gelatinous oxide.crystalline trihydrate is almost insoluble cold acids,although it dissolves readily in hot concentrated H2£GA .It m ;0yt. It is therefore similar in properties to aged gelatinous oxide.There is thus a II a gradual transforation,through ageing,from an amorphous material to the crystalline tri-hydrate.Eewly formed gels consist solely of anhydrous AlgOg with adsorbed water* -Jh6_aydrous Oxides — McGraw -Hill — 1926 - vVeis^s Clarke* allows that the action of water on corundum results in the formation of diaspore,out that further action by coincident salts .produces gibbsite ,among other minerals. Data of Geochemistry - U .S .G .S .?Bull .770 .1924 .p.344 -01a.rlw» It would appear then that,on the whole,the tendency is not towards dehydration,as suggested by Holland,but rather towards hydration,with gibbsite the most stable form under normal weathering conditions. T h e m o s t recent and comprehensive description of diaspore,gibbsite and cliachite from the point of view of their optical properties is to be found in "Shin-Section Mineralogy" by Rogers and Kerr*.Incidentally it Is pfcsmted out that diaspore is commonly a product of anamorphic action,more than it is of katamorchic. ,; Sh i n-Section_Mins ra1o ay - aaGrav - Hill .1955 — Sogers and Kerr.-p.176 The two groups of hydrous oxides here treated comprise the most common representatives of this fasti ly resultant upon weathering.Although others may exist they will not ba treated here. Hydrous Silicates " Two recent papers by Boss and Kerr* represent the most recent and authoritative work on the subject of the hydrated aluminium silicates and will be quoted from extensively in describing these minerals. She Kaolin Minerals - U.S .G . S . ,Prof .Paper 165-13,1931 -Boss and Kerr —Hallpysite and Allophane - " , " " 165-5.1935 - " and " II molecules of essential water.Optically i t differs very slightly from muscovite except in exhibiting a slightly lower birefringence. In this connection it is interesting to note that Bies* mentions a distinctly micaceous mineral.whose single and double refraction are higher than kaolinite but lower than muscovite.and which apparently ex-hibits an isomorphous gradation between muscovite and kaolinite,marked by a gradual loss of potash and addition of water.3y experimentation he proved that muscovite was found to change to'hydromica'after immersion in pure or carbonated water for a year. Glay3 .Origin,Occurrences and Uses -John m e y and Sons,1927, — Chapter on Play Minerals - Bies Lindgren* also remarks on the apparent partial alteration to kao-Unite exhibited by sericite in many cases. J;he Origin of gaolln-Eoon.Seol.X.ms,^-89-93 —Lindgren Kaolinite is insoluble in all but concentrated sulfuric acid,and then only when boiled in it for some tlae. Boss and i£err* also sake some other Interesting observations on the subject of kaolinite.Shey show that most of the vermicular crystals of this mineral must have developed in place,either as the felspar or other aluminous source material was being altered,or through recrystall ization of amorphous or submicroscopically crystalline kaolinitic mater-ial after its transportation and redenosition. - She Kaolin Minerals -U.S.G.S?Prof.Paper 165-£,1931,p.l73 —Boss and •—*,••••.' . i • — —;—- . • • • ' • ,- - • ~ • - i£err Another feature* Is the evident replacement of quartz by kaolinite which has been effected in a number oS samples studied. * Idem. - t\. 174 ' 1 ~ : : iously unnamed,is termed dickite. ' The data presented in this paper show that the chemical composit-ion of these three minerals is very similar.iCost of the kaolinite and all of the dickite and nacrite investigated hove the commonly accepted formula 2H 2 0 .Al 2 Q 3 . 2Si0 2 ; some kaolinite varies however in the silicas alumina ratio,its high silica representative,anauxite,being possibly 2H 20.Al 2G 3 .3Si0 2e* 'The optical properties of kaolinite and dickite are quite distinct and these two minerals can be readily distinguished where crystal grains are available.Saerite is close to kaolinite in its optical properties.' 'The three minerals are stable at different temperatures and so may have formed under different conditions.abst if not all commercial kaolin deposits that are characterized by kaolinite are formed by the weathering of felspathic rocks.Some kaolinite is also formed b,:y the act-ion of sulfate -bearing or thermal carbonate-bearing voters.Dickite .stab-le at higher temperatures,appears to result from the action of moderately heated hypogene solutions.Eacrite also appears to result from hypogene processes of slightly higher temperature.' The various properties of these three minerals are treated in soma detail in this paper(The Kaolin Minerals-Eoss and Kerr) and will not be repeated here. An exceedingly interesting point is brought out in this paper.It has usually been asserted that muscovite is an intermediate product in the weathering of felspar to kaolin,but the work of Boss and Kerr would seem to show that this intermediate material is not muscovite at all,but a clay that is probably similar to kaolinite but with one instead of two II * 2 h e w o r k o f E o S 5 has shown that the kaolin minerals can not Da assigned to a definite species.and they present evidence to show-that three distinct mineral species are represented .For preliminary discussion those species are called the mineral of kaolin,Dick mineral, and nacrite.In this paper the terms kaolin and kaolinite are used rep-eatedly,in quite definite senses.Sy kaolin Is understood ths rock mass which is composed essentially of a clay material that is low in iron and usually white or nearly white in color.She kaolin-forming clays are hydrous aluminium silicates of approximately the composition 2H2G.Al2<$s3„ 2Si02 ,and it is believed that other bases if present represent impurit-ies or adsorbed loaterial.Zaolinite Is the mineral that characterizes most kaolins,but it and the other kaolin minerals may also occur to a greater or lesser extent in clays and other rocks that are too heterog-eneous to be called kaolin. ' ' The kaolin minerals.described in the first paper, are not the dom-inant constituents in most clays .shales, and soils,as has been previous-ly often assumod.ilven a casual inspection under the microscope of the clay material in these rocks,shows that it cannot be one of the kaolin minerals,all of which have very low birefringence,but Is most commonly one of the beidellite-montmori1lonite type of clay minerals which have a moderately high birefringence.' 'Kaolinite.which has heretofore Included all three minerals,is res-tricted. to the most abundant one .which characterises all or nearly all kaolin deposits.Eacrite is an old name applied to a mineral from Brand, Saxony .which is revived for the mineral whose type cams from that locality fckird mineral,originally described from the Island of Anglesey,and prev-:*"-••' - 4 5 In a second paper*,Kerr and Boss deal with, teo more minerals of this family:halloysite and allophane. * Halloysitevand Allophane —U.S.G.S. .Prof.Paper 165-3-. 1934-Boss and Kerr TShis study shows that halloysitevis a fourth mineral of the kaolin group,closely related to hut distinct from kaolinite.Halloysite has prev-iously been described as amorphous,because commonly the microscope reveals no evidence of crystal structure.X-ray diffraction studies,however,show that it has a crystal structure,being made up of crystal grains of submicroscop-ic size.Halloysite appears to be always the result of weathering or super-gene processes,like kaolinite but unlike dickite and nacrite,the other kao-lin minerals,which are commonly the result of hydrothermal processes.5 general there are two types of halloysite- one that is usually white or light -colored,porous,friable,and almost cottony in texture;and another that is dense nonporous,and porcelainlike.The white or nearly white halloysite associated with kaolin deposits is difficult to distinguish from the very fine grained kaolinite,and both types of material may be associated with the coarser-grained,obviously crystalline kaolinite.' 'i'he generally accepted ratio for halloysitevis Ai 2G g .SIG 2 .H20.A comparison of the analyses of halloysite with those of kaolinite indicates that halloysite is richer in alumina than kaolinite-that is ,kaolinifce tends to be somewhat closer to the ideal formula 2H 20.Al £0 3 .2Si0 than halloysite .although anauxite,the high silica end member of the anauxite-kaolinite group has a silica retio of 3 ; 1 . ' 'Under the microscope halloysite shows very faint to no birefringence. It is generally conceded to be at least slightly soluble in dilute HC1. • - • • < . • • - . . • 46 'Allophane is an amorphous material that is commonly associated with halloysite.lt has no crystal structure and no definite chemical composition,, Th name allophane,they suggest,should be restricted to mutual solutions of silica,alumina,water,and minor amounts of bases but should include all such materials,even though the proportions of these constituents may vary.' •The literature is full of references to different "clay" minerals, usually indefinite in character and incompletely described.Many of these are without a doubt synonornous with some of the minerals described above. There are ,however,several other distinct minerals found in residual dep-osits and associated with kaolin material.Some of these will be described below,their characteristics being taken from Hies* V'Clays,Occurrences, Properties,and Uses."* Clays,Occurrences,Properties,and. Uses - John Wiley and Sons.1927, MM Chap, on Clay Minerals — Sies Beidsllite (AlpOg.SSiOg.xHgGj ilonoclinic,known only in plates with indistinct boundaries,usually microscopic in size.Lastre vitreous to wasy,with color ,white.reddish or brownish-grey.Befractive index less than G.B.(1.517).birefringence fairly high (.032).Approximately uniaxial,27 - 9-16 deg.Perfect cleavage,001. Member of Montmorillonite-Beidellite-Eontronite series. Ifontmorillonite (Mg0.Al20g.BSiOg.nHpO) ilonoclinic .nearly always in fine scale-Iike crystals.Color-colorless ,greenish,or pale pink.Hefractive index below C.S . (1.50),birefringence fairly high (0 .021) .2V — 10-16 deg..cleavage perfectool when present. Difficultly soluble even in hot HOI. Kontronite (Fe 20 3 .3SI0 2 .na 20) Monoclinic.color,yellowish-green,occurs as plates and fibres. II Refractive index higher than 0,3..birefringence,high {.036)Micaceous c l e a v a g e . - l a r ^ .Easily decomposed by acids and strong alkaiis.End mem-ber of series Sonnorillonite-Bsidellite-llontronite. Only one more really important mineral,related to this group remains-the mineral alunlte.This mineral,as described by Rogers:ana Kerr%is a finely crystalline mineral,with the f^xxola m 3 ( 0 H ) 6 ( £ 0 4 ) 2 o I t i s ^ of hydrothermal origin,but has been described as an alteration product, resultant upon weathering processes.lt is hexagonal In form,and occurs as fine to coarse aggregates.Refractive index is slightly above C.B.,and birefringence is in the second order colors(0.020}. aese In general the determination of all these secondary minerals is an extremsly d i f f i c u l t y not impossible,task without the aid of the X-ray and dehydration tests.Although the subject has only been touched in this section,It is felt that further mention and detailed description of the minerals is unnecessary in view of the excellent references available. Amongst the most valuable of these are the aforementioned papers of Ross and Kerr as well as others,listed below: (1) The Kaolin I-Iinerals - U .S .G .S . , Prof .Paper 165^,1331-Boss and Kerr (2) Halloysite and Allophane -U.S.J.2.,Prof.Paper 185-3,1934 -Boss and Kerr (3) Thin-Section Mineralogy -McGraw-Hill,1933 -Sogers and Kerr (4) The Microscopic Determination of the Nonopaque .Minerals -U.S.G.S.,Bull.848,1934-Larsen and Bermun (5) Clays,Occurrences,Properties and Uses- John Wiley and Sons, 1927 -Ries II _Jjf.i DecomposIt ion of Specific lunerals •^feathering of Orthoclase Orthoclase being a combination of a very strong base and a weak acid is easily hydrolzed. K 2 0 .Al 2 0 3 . 6S i0 2 plus SflgO - 2XoII plus A1, Og. 2210£>. 21^0 plus 4 SI0 5 tmi The above formula is a composite one and mice3 no attempt to analyze the various steps in decomposition.In actuality the above reaction may rarely take place directly,there being considerable evidence that the first stage is the production of 'hydromica'(see page } , o r possibly even sericite.This sericite loses £ and takes on *ater,until the nearly X free hydromica(muscovite~like kaolin mineral of 3oss and Iferr-see page ) is reached.This mineral,Al 20g.2Si0 2 .H 20,is gradational between sericite and kaolinite.being transformed to the latter by the addition of one mol-.ecu!© of water. The hydrolyaation of orthoclase releases which combines with OH to form caustic potash .Silica is set free and will likely go into colloid-al solution.lt is probable that hydrolysis also releases at leasta port-ion of the A1 20 3 in the colloidal state as well.since both halloysite and allophane are known to be produced by the decomposition of orthoclase. Some of the K,otherwise removed, in solution,will undoubtedly be caught and held by these colloidal aubEtancc-s.SiC2,in excess of that required for the formation of sericite.hydromica.kaolinito,etc..nay be removed in colloidal solution,deposited as secondary silica,or raized with indefinite amounts of colloidal AlgQg and adsorbed bases to form allophane. There are many reported eases In which kaolinite is considered to res-ult directly from the alteration of felspar,and many others in which true II sericlto is the sain product.Again ,the hydrous oxides of alumina are not uncommon decomposition products.Just what the governing factor is which determines what course weathering will take is,as yet,not satis-factorily determined,although it is generally concluded that the ph value of the solution present controls the formation of these minerals and the combination of the colloids. When dissolved carbon dioxide is present the reaction is increased. This is due ,no doubt,to the fact that the CC2 combines with the released bases,thus tending to prevent equilibrium from being established. In cases where there is evidence of volcanic or solfataric action orthoclase is largely converted to an aggregate of white mica. Although.as seen above,the process is largely gradational and some-what variable,the usual products resulting from the decomposition of potash felspar are kaolinite with associated halloysite and allophane, hydromica,and sericite. Both kaolinite and sericite are frequently arranged along concentric sones of growth In the oithoclase,giving ,thus,seceral rings of altered felspar separated by fresher bands.In other cases they are arranged along cleavage cracks.Usually ,however, the shreds are unoriented and are scat-tered irregularly through the crystal,or are arranged in clusters^gener-ally in the centers and not around the borders of the minerals.Johannsen* A Descriptive Petrography of Igneous Hocks-Vol.il,Univ.Chicago Press — — • — — 1952 .p. 144-Johannsen POXKts out that this grouping makes It seem probable that these minerals were produced by changes which took place contemporaneously with,or shortly after solidification,when conditions,as of heat,were changing. II liarely epidote and zoisite have been reported as decomposition prod-ucts of orthoclase.This is only possible.however, by the addition of calcium and iron,derived from the breaking down of ferro-raagnesian min-erals. Whether zeolites m y - result from tho weathering of orthoclase is a sons what controversial Point.Stephenson'reports the formation of analcite artificially from this mineral,but in general since there is no pure E zeolite known,this reaction would involve the addition of Ea.llodern opin-ion seems to substantiate the delegation of the zeolites to a group of minerals formed1 by the alteration (katamorphicj of subsilicic volcanic rocks for the most part. - The Action of Certain Alkaline Solutions on Felspars and Hornblende-Jour.Geo1.XXIV ,1916 ,pp.191-196 ,-Stephenson ,1, ,Thin-Section J|ineralosv - McGraw - Hill .1933 —Sogers and gBrr •decomposition of Plagioclase As in the case of orthoclase,the hydrous aluminium silicates form the most conspicuous decomposition products of plagioclase,the reactions involved being comparable to those described for the former mineral. Here again a mica-like mineral is nearly invariably present.In this case,however,should it be a true mica,it must be secondary paragonite and not true sericite.As before,hydroaica,is usually conspicuous. Decomposed plagioclase .rich in lime,usually yields a good deal of calcite ,and often zoisite,and certain members of the chlorite group.A mixture of calcite,zoisite,and more or less chlorite forms the opaque white,eream,or greenish colored substance known as sau3surite,common to gabbro.For the formation of zoisite and epidote ,iron and magnesia must II added.She following formulae are included,not because they represent the actual chemical reactions involved,but because they illustrate pos-sible products and relative amounts of material available for combination, _ _ kaolinite (1) Ka 2 0 . ,a 2 03 .6Si0 2 plus 2HgO plus C02 2 3 i O ^ O t,mH 4Si0 2 plus Ka2G03. ( 2 ) ^ a 2 0 « A l 2 0 3 . 6 S i 0 2 ) plus 2H20 plus 2C0g — Pi™ 12 SiOgplus 2Ea2C0g (3) 8 (6a0 .Al 2 0 3 . 2Si0 2 ) plus K 2 0 .Al 2 G s . 6Si0 ? plus 4H?0 muscovite zoisite J k ^ m z O z z m O z i m z O plus 2(40a0.5AUfo.6Si0n.HOQ) pins 4Si02 (4) 2(Ca0 .Al 20 3 .2Si0 2 ) plus K 2 0 .Al 2 0 3 . 6S i0 2 plus 2G0? plus 2H?0 -muscovite calcite . ^ a ^ M i s O g i G S i O g i ^ H g O plus 2CaC0? plus 4 Si0 2 The alteration of plagioclase to scapolite was described by Judd*. However,here again,the association is somewhat unusual,although more common than it is for a more highly silicic mineral. On the process by which a Felspar is converted into Scapolite par-_:Be.c propositi on of Mica, a Muscovite Under the head of muscovite are included both muscovite and agonite,the potash and soda -bearing micas respectively. ' These minerals are very stable,being but little affected by weathering processes.As nentioned previously( page ) ,howeverMuscovite on being exposed to the action of pureor carbonated water for a consider-able period of tine will lose potash,at the same tims becoming more high-ly hydrated. Blotite Upon weathering,biotite frequently takes on a golden lustre,which under the microscope often appears as bleaching,so that in many cases biotite resembles muscovite.Usually between the lamellae of altered bio-tite, the re are deposited ,grains of quartz.caleite,and limonite,the lat-ter giving it a yellow color.Commonly the alteration consists in a change to chlorite.Accompanying this change,there is frequently also a separation of epidote.usually between the lamellae of the biotite,where it forms elongated lens-likenpatches. Yan Hise* gives the following equations for possible changes: ^ I l i i i i M S I o i l ^ t ^ ^ f e i ^ - U . s X s . cls.1 ori ts fiKHMg2Al2Si5012 plus 4HgC03 plus 6H20 - 2(H22,Ig4Il2Si3012.4aa) plus KgCOg plus 3C0g 30KHMg2Al2Si3G12 plus 6Fe203 plus $0 GaCOg plus 35002 plus H ?0 — epidote • • -4 (H 5Ca 1 0Al 1 2Fe 3Si3.50^} plus 30Si02 plus 12A10(0H) plus 6Qi%G0s plus 15KgC03 The above equations represent the decomposition of iron-free biotite. In general.however,iron is widely variable in biotite and some iron ores are usually liberated.With still further alteration,the chlorite itself passes over to quartz.calcite.kaolinite,and iron.oxides.Titanium-rich biotite breaks up into chlorite and titanitej or there may be a separation of rutile needles. •J^athering of Anrohlboles and Pyroxene a The alteration products of amphiboles and pyroxenes are essentially the sane .consisting of chlorite,calcite,hematite, magnetite,quartz,etc. Johannsen^gives the following formulae to illustrate these changes: A Descriptive Petrography of Igneous Hocks-Univ.Chicago Press,Vol.II — .... • _ _ «i).199 .-Johannsen _ Hornblendes 53 8OaO.l6l.isO.32SiO2.8FeO 8%0 .8Al 2 0 3 . 12Si0 2 . 4Fe0 .4Fe 2 0 3 * 2 1 H2 ° P1 ^ 16 COg chlorite epidote ~2 ( l2%0 . 3Al 2 O 3 . 7S iO 2 . l 0H 2 0 ) plus (40a0 .2Al 2 0 3 .Fe 20 3 . 6Si0 2 ,H 2 0) plus 4GaG0s plus 12FeG0s plus 24SiOg plus 2Fe203 Piopsides serpentine 3(Ca0.Lig0.2S102)plus 300g plus 2H20 —(3£ig0.2Si02.2fi20) plus 4Si0 2 plus 3CaC03 usually diopside contains iron and alumina,so the decomposition products include chlorite.magnetite,etc. Augite gives rise to the sans alteration products as diopside. There is a marked tendency for the pyroxenes to revert to amphiboles of an approximately corresponding composition,the process being known as uralitization.In some eases a reaction occurs between augite and iron ores,giving rise to a hornblende richer in iron than the original augite. Often ,however,secondary hornblende is very pale in color and say best be described as ectinolite.with characteristic blade-like or fibrous struct-ure. Anstatite is usually converted into a form of serpentine known as basfcite t bastlte 4(S%0.Si0 } plus C02.-.plus 2H2C —3Mg0.2Si0r>.2H20 plus SgCOS plus . . . . " • 2Si02 , The usual result of the weathering of mixed femics is the formation of a mineral of the talc or serpentine class .restating from hydration of the magnesium molecule.If lis© is present and the groundwater contains carbon dioxide,dolomite may be formed.If the original minerals contain a fair amount of alumina,a member of the chlorite group will result. Ferrous ikon may form a carbonate,or may enter into a chloritic mineral. II She most common effect is more or less complete oxidation,usually to some form of brown hydrated ferric oxide,less commonly to hematite or magnetite.Lime carbonate usually gives rise to a carbonate,calcite or dolomite ,or is leached out altogether.In some cases the femics have been converted to a member of tho epidote group,although tin general,secondary epidote is aerivedcfrom Urns-felspar. The final result consists mainly in the separation of magnesia,mainly a as carbonate and talcose minerals,of iron oxides,and of calcium carbonates. Most of the silica is acrried away in colloidal form. Weathering of Olivene The ordinary olivine of basic and ultra -basic rocks is always an isomorphous mixture of orthosilicates of magnesia and iron,and sometimes with a certain admixture of the corresponding litre silicate molecule. Iron silicate breaks up completely,yielding various oxides and hydro-xides according to the degree of hydration possible.The first products may be either magnetite or hematite. The lime molecule , i f present,gives rise to calcite.The decomposition of magnesium silicate is the simple one of hydrolysis,the product being serpentines serpentine 2Mg2Si04 plus 3H2G —3MgQ.g£10R,.ia20 plus MgCGS Somstisas serpentine undergoes a further decomposition,the final prod-uct being/IgGGg. Accessory .Minerals AndalusJLte - usually alters to muscovite .although kaolin has II been described as an end product. Apatite - rather soft and soluble in acids —Cornudum*- alters to muscovite,diaspore.gibbsite,spinel,elischite, silliiaanite.cyanite,andal«site,parasonitetpyrophyllite,felspar,zoisite, margarite,chlorite,and chloritoid. '5 Corundum,Its Alterations and Associated Minerals-Proc.Am.Phi 1.Soc. , XIII.1C73.pp.361-405 -3snth * Pluprjt^ - alters to calcite by the action of percolating waters containing calcium or alkaline carbonates. Garnet - resistant,but alters to chlorite. .Jlmenite-frec.uently alters to secondary titanium-bearing minerals, the mixture of these alteration products being called leucoxene.Mth further alteration there is often a mantle of transparent material around a remnant of the original material.This outer shell is generally secondary titanite,in some cases an admixture of rutile being presenter possibly even anatase or perofsuite.In a further stage the original mineral is completely altered and there remains only a leucoxene pseudomorph after ilmenite.In some cases secondary calcite and epidote accompany the leucox-ane, , . . . . . gematite and Magnetite - may ba themselves secondary to tend to alter to liaionlte* alters to hematite and lirnonite,action commencing around the edges. •  • ..Rutllg- alters to leucoxene,sometimes titanite,anatase ,or perofskite. In general quite resistant. Spodumene - alters to muscovite and albite II Titatfite - say alter,in granites to an earthy substance accompanied by calcite,or to anatase or to ilmenite.In rocks other than granites it has been found altered to perofsklte and rutile. Tg&az. -resistant,but alters by the action of alkaline solutions to muscovite.Xaolinite amy be represented as an intermediate product. So far no mention has been made of the felspathoid group.Eepheline being the most important rock-forming member of this family will be here described: Sepheline The main action in the weathering of nepheline seems to be that of hydration.The mias cancrinite has been used to describe a substance prod-uced by the alteration of many nepheline-bearing rocks.This mineral lik-ely consists of a mechanical mixture of soda-mica,calcite,and other molec-ules, the line moleciile having been introduced from the outside. Sodalite may be an alteration product after nepheline with that intro-duction of G1-. ' Hote- The above description of the alteration of various minerals is taken ,for the most part from JohannsenS !,A Descriptive Petrography of Igneous Hocks",Ohiv.of Chicago Press,1932,Vol.II,pa which the subject is treated rather fully..4 certain amount of the information is compiled,how-ever,from various sources. laLStudles on the Alkalinity of some Silicate Minerals In a very recent paper Stevens*makes sons very interesting observat-ions on the alkalinity of a number of different silicates,and the bearing this property has upon their susceptibility to decomposition. II * Studies m the Alkalinity of Sosa Silicate l&inerala -U.S.iTFTf Stated briefly this paper deals-with the following subject; • - 'By grinding isinerals under water it -has been found that they yield relative and reproducible aoasurecsnts of the hydrogen -ion concentration resulting frost their h y d r o l y s i s . s i l i c a t e s and t»o glasses have been studied in this way by a color!saatrio aettoa of determining hydrogen-ion oonoestratio&,ai& -so® of them have he&n studied sore qaaatltfttlvely by oaaae of the hydrogen electrode.fhe results of these tests are a rough l D d o z o f t h 0 woafcfcering qualities of tae different Mnerals tested.' M m m tabulating the results obtained,it sight be voll to review briefly the fandaosntal ideas involved. 'Water ionizes to a moderate eztent.yieldiag hydrogen and hydrosyl iocs, slight but do finite,and is pure t»tsr the number of hydrogen ions w u l d be- the m m m the nuabar of hydroayl ions.Shea other substances are pres-e n t L n % ' m »*t®rtfaowover,these teo nmabars are cot.in generalqaal.under such circumstances use is M e of the fact that the product of the concen-concentration of oa le increased.Ic order to Maintain the constancy of to for© un-ionised water.In a sivaii&r asnacr acid increases the fl* concen-tration and reaoves OH from solution.* II two concnntrations are so simply related it is sufficient for most purposes to consider the hydrogen-ion concentration alone.Such concentrations will be expressed as a negative power of 10.The figure following the negative sign is characteristic for each concentration and has been called the ph. number-for example,7 is the ph number for pure water or a neutral solution .as noted above.'" -' At neutrality pH and $0H are both 7.Thus the concentration of either ion in solution is given simply by ph.it being understood that ph-7 signif-ies neutrality,that alkaline solutions are at ph greater than 7,andacia solutions less than 7,and that an increase in ph signifies a decrease in hydrogen -ion concentration or,in general,in acidity.* ' I t becomes evident,from what has been said of the ionization cf water, that the strength of an acid or base is dependent on the extent to which it ionizes into H and OH ions in solution.A salt on hydrolysis reacts wit h the water ions to form an acid and a base.Silicate minerals hydfolyze in the sanfc way,ana being combinations of strong bases and weak acids,give an alk-aline reaction.' . It may be seen,therefore from the above that the degree of alkalinity ,in other words the amount of hydrolysis?is a relative measure of the power of the silicate in question to resist ,or yield to weathering by chemical decomposition. A number of different silicates were tested ,and the following may prove of interest at this point: Orthoclase Olinochlore Albite Labrador! te Mineral •pH value 9 .0 9 .2 9 . 5 9.6 100 Epidote 10.0 Actinolite 10.0 Phlogopi t© 10 . 1 Diopside 10.1 Hornblende 10.£ Olivine 10 .2 Pyroxene 10 .2 In general the above list agrees fairly closely with the observed facts in connection with the relative susceptibility of the various min-erals.However it must be reaembered that no really hard and fast rules can be laid down as to the order in which minerals will decompose under a ceri&in set of conditiond. ~ leathering of Some S-geoific Bock Types A few examples of the normal weathering,under te asperate conditions of som members of the commoner rock types might assist in clarifying the general subject of katamorphisra. Sranite The katamorphism og graiaite does not always consist simply in its weathering,for certain earlier changes may occur,as emphasized by .Johannsen** * A Descriptive Petrography of Igneous Kocks-Jniv.of Chicago Press,1932 , . ,' 7o l . I I ,t>.209 -Johannsen "These post-volcanic changes are generally recognisable under the niic-roscope,even in rocks which are apparently quite fresh raegascopic&Ily* Among them are the resorbtion of biotite and hornblende,the uraiitization of pyroxene,and the alteration of felspar to kaolin,sericite or other col-orless mi ca,epidote,zoisite,quartz,etc.Further there may be an addtiron of naterial,such as quartz,from external sources,either by deposition from solution or by assimilations of the inclusions of the country rocic.In many 100 cases rocks,which have been tinder pressure,during- or subsequent to their formation,show minute cracks extending through adjacent minerals.These fis-sures may have subsequently become filled with quartz or with a quartz-fel-spar aggregate.In rocks with catac&astic texture,fragments of felspar are united,in many cases, with a cement of felspathic material,clearly subseq-uent to the crystallization of the original material,and .although formed before the solidification ofthe whole magma,in a %my expressing an alterat-ion of the original Intention of the rock." Weathering embraces both disintegration without decomposition,and dec-omposition .^ former process results in the formation of grus by the break-ing apart of individual grains,owing to unequal coefficients of expansion of minerals of different competitions or to the penetration and freezing of water.This material differs very slightly in composition from the original granite. By the processes- described in detail earlier in the chapter,the granite is attacked,the rapidity of alteration depending greatly upon the physical condition of the rock,that is to say,its porosity,the presence of fractures and joints,freedom from overlying mantle and other factors.Srns affords a very susceptible material to the processec of decomposition. In the weathering of granite,the various component materials are more or less altered to laterite,gibbsite.colloidal aluminium silicates,etc.The principal change is the alteration of the felspar to a claylike decomposit-ion product,probably a colloidal aluminium silicate.This is cooinonly known as kaolin,but in reality.may contain other secondary products.The subject of kaolin and its modes of formation will be dealt with under a separate head. Suffice it to say that kaolin is known to form,under suitable conditions,from 100 the weathering of felspars. The ferro-magnesian minerals of granite also alter readily and give rise to chloritic and talc-like substances and red and yellow-oxides of iron.Quartz remains fresh, {fart of the altered material may be carried away in solution,but practiaclly all of the quartz and iron-oxide remains be-hind. Quarts,probably,is actually,as well as seemingly,more abundant in the decomposition product than in the original rock,owing to its secondary for-mation from felspar.Si02 however, decreases. Merrill* gives the following analyses of fresh and decomposed granites from the District of Columbia. I S g M ^ l a S ^ g a i i ^ P j g ^ a n A Soils- aacalllan 11921 .p. I86~^lerrTTT afresh C-r&y. Brown.but raoder-Sranite atelv fira ^onsti tuents Ignition BiOg TiSg IfeO Pe203 OaO ago. • S&pC £20 P2G 5 •esldoal. Sand o CjCJC 69.33$, 14.33,% Eot det. 3 .60% 3.21% .... 2.67jb 0.10% 99.60/O Z+2.1% 66.82% is.ezfl not det. 1 .69$ 1.86/fc 2,76ft 2 .58^ 2 . 04$ not det. 99.76?S 4 . 70$ 65.69?$ 0.31/i 4.33)1 2.63 2. 2 .1 2.00,1; 0106^ 99.7® The climate of this region is somewhat capricious,the Weather Bureau records showing extreme ranges of -15 deg. to plus 104 deg.P.while an ann-ual range of 10 to 95 deg. is common.The average annual temperature is 54.7 dgg.F.,and the average precipitation is 43.96 inches. • It is at once apparent that there is a surprisingly small difference in ultimate composition between sound rock and residual sand,the more mar-ked differences being a slightly smaller amount of ailica.nore alumina,and slightly di.-sinlshed amounts of lirns ,magnesia,potash,and soda.wit-i a eonsld 100 erable increase in the amount of water.The ferrous salts.moreover,have been converted into the ferric form. i3y recalculating the analyses of those rocks,assuming Fe constant, Iferrill* arrived at the following results Idea .u.189 Changes from fresh rock to Hesidual sand Gons,tlti;onta, foosa for entire % each constlt- j each con-uent saved stituent lost f i C 2 10-50.5 85.11% 14.89^ 2 3 36,77% z.ZZt FfeG Fe 20 3} $ ' 0 0 100,00 o.OO 0 a 0 0„8l£ 74.79/b B5,2lf 0.36£ 98.51^ 1.49% 0,77% 71 .38* 28.82JS-V J O.Q5% 68.02$ £2Gb 0.047* 60,00% 40.0% The above figures show,in general,the effect of the weathering of gra-nite in a temperate climate.The results of typical weathering in a tropical climate are usually materially different from that experienced in a temper-ate region,and for that reason,a discussion of this subject will be postponed •until the next chapter. Weathering of Granodiorite In general,granodiorite weathers like granite,and the chemical changes mentioned in connection with the latter,apply here as well.flue to the greater proportion of calcic felspars,however,granodiorite is more susceptible to chemical decomposition. Weathering of Eepheline Syenite Merrill® gives the following analyses of the fresh ana altered elaeol-ite syenites of the Pourche Mountain region of Arkansas.The rock weathers 100 away to a coarse grey gravel 'which ultimately beeORBS a clay,from which,by washing,may be obtained pure,or fairly pure kaolin. ^Constituents. ,., Fresh Syenite Deoomp.Syenite Kaolin-like r»sta«ft S i0 2 69.70^ a 1 2 ° 3 . 18.85/* Feo0 4 . 8 5 $ Gau 1 IgO ' 0 . 66% Kz 0 5 .97^ la 2 G' 6.29% H 2 ° 1 .88 % 39.56% 0 .44^ j}jC a 1,96% 1.31% 6*8.5^ '97.56%' 38.57Ji X«3 S/i/ 0.34/5 0.45% 0.25% 0.37JE 13 .6l£ 101.oo£ Idea p.196 Calculated Loss of Saterial from Fresh rock to kaolin-like residue. Constituents -jL.lQ.ss. for entire ...f each constit-. roc k SiQg *J t A1 2 0 3 0 .00 Pe 20 S 4.19JC OaO 1 .19$ % G 0.57% 5.90% KagO 6.15% h 2 ° 0 ,00 55.28% uent saved % each constit-uent lost 3 7.62,t-100.00^ 13.83J5 12.10JS 18. •Se-SSj® 100.00/1 62*16% 0100J5 86 .17^ 87.90% 82.1036 81.65% 97 .11$ 0.00X i-he greater percentage decrease In silica in this rock,over that in granite,may be explained by the fact that all the silica in the .syenite is combined in the form of silicates,quartz being absent. Weathering of Phonolite Merrill* describes this rock and its alteration as follows: Idem .P.19S "This phono lite , it should be reiaarked, consisted essentially of sanidine felspar and a soda zeolite,together with accessory augite,black mica,magnet-100 ic and titanic iron,and -possibly hauyne.The zeolite is assumed to have origin-ated from the alteration of the nepheline.The process of decompesition would seem to consist,then,in the breaking down of this zeolite,and the conver-sion of the rock into an earthy mass,with little other change,so far as ult-imate composition is concerned,than a considerable proportion of its soda, and an assumption of nearly 3.5% water.The sanidin appears to have undergone only a physical disintegration,the decomposition being limited to the other constituents.The rock weathers into a bright colored,porous,friable mass." weathering of Basalts Merrill* describes the decomposition of a Bohemian basalt as follows; 'Idem »t>»205 "In the case of ths Bohemian basalts,thevdeconposition commenced with the formation of boulders.which,*hen the process had not gone too far,still showed fresh unaltered basalt interiorly,but teoue more and more decomposed toward their peripheries.The first stage of alteration.it will be noted,con-sists ,aside from hydration,in a slight apparent loss of silica,a consider-able oxidation of the iron-aiagncsla minerals .accompanied by a slight loss of both constituents,and an almost complete loss of alkalis.In the second stage.lime and magnesia are both lost in considerable amounts,the iron pas-sing over wholly to the condition of sesquioxide.and there is a further alight diminution in the proportional amount of silica.It is evident that here the felspars were the firfife to yield to the decomposing forces,the oliv-ine and augite proving more refractory.The total loss of material,it will be no ted, amounts to 43.96^,the line .magnesia, alkalis, i-ronosridos, and silica dis-appearing in the order here mentioned." 100 Weather ins of Dlorite Quoting lisrrill* idem.p.POS »Tae rock here(Albemarle County.Va.) was fine-grained,of an almost coal black color finely speckled with whitish flecks due to the presence of fel-spars, 'fhe microscope showed it to be composed mainly of hornblende with inter-stitial soda-lime felspars and scattered areas of titanic ore.The clay,or soil,to which it gave rise,was deep brownish red in color and highly plastic, though distinctly gritty from the presence of undecosrocsed minerals," Constituents Fresh Diorite Pecomnosed•Diorite SiCg ' AlgOg FepCg OaO HgO &ZQ &20 ? 2G5 ilgO 46.7Lj£ 17.6l£ 15.79 % 9.46 % 0 * 55%-<Se©a/5 0.25 ,t< 0.32^ 42.44*' 25.51^ 19.20£ 0.17% 0 * iSl^ b 0.49£ 0.56%- . 0.29% 10.92% 100,0l£ 99.9% . Shere was a calculated loss of 37.51$ c jf constituents daring decompos-ition. Slather ins; of Ultra Basic UncTra Quoting Merrill*: "uJhe ultra basic rocks-p^ridotltes and pyrox&tiitee -from the Vory nature of their composition,,trast y ield ,on decomposition,residues poor in the aik-alis and rich in iron and magnesium and aluminium compounds.Owing,further,to taeir poverty in alkali-bearing silicates,the process of decomposition must oe less complex.consisting essentially in hydration,oxidation,and a product-100 ion of iron,liaie and asegoes ian carbonates and a liberation of ohalcedonic silica," "during the process these rocks,as a rule, beeosfc brownish,and on the surface,often irregularly cheeked with a fine network of rifts which bec-ome filled with secondary calcite,magneslto,and chalcedony," In the foregoing section an atte-apt has been m&de to clarify the sub-ject of roc k-weatnoring by giving soma concrete examples.These are but ind-icative, and again it nust be emphasised that in the realm of weathering few if any laws can. be set out to govern decomposing processes and their effects. rtlth tais last section this chapter will be closed,leaving tae more specialized subject, of weathering under tropical conditions to be treated in soma detail in the nest chapter. M o l l p gr a-ohv S h e following direct references,in t h e order of their o c c u r r e n c e , were Bade I n the coarse of this chapter t U) A treatise on Metamorphisra - 2US,G,S«,2&m.47,1904 -Van Hise (2) Metanorphic Geology -Henry Holt and Go. ,1916,-Xintro.p.xxi-r?) > * „ Leith and Mead (-J Beaistrioution of Sleasnts in Formation of Sedimentary Socles — Jour.Oeol. .Vol.XV,So.3,April-May 1907 — M e a d (4)£xfoliation as a Phase of Hock Weathering - Jour.Oeol. . V o l . m i l l , So.5,Eov-Dec.,1925,?p .805-8Q6-Blac to,-elder (5)Data of Geochemistry - U . S .G . S . , Bnl l . 7 7Q , 1924 f p . 4 63 - Clarke (S Etching of Quartz in the Interior of Conglomerates- Jour .Oeol . , 1 9 0 2 Vol .X ,p .815 —Fuller (7)Solution of Silica under Atmospaerie Conditions - 3ull,Geo.Soc.Ata., Vo1 .8 , «ar .6 ,18 9 7,p213,Hayes (8jBocks,Bock-v,'eathering and Soils- & i c m i l l a n , I 9 £ l , p . 2 5 2 - Merrill U 0 J " « ,p«221 - -(11) Cl.ayS,Occurrences,Properties,and Uses - John Wile? and Sons 19P7 P«2 , B i e s (12J Mineral deposits - McGraw-Hill,1928,p.362 —Li •jurmgren (13J Terro B o m in Sao Paula,Brazil ^ o n . O e o l . , r o l . J O T , B o . 3 f & y 1934 p.880 ,-Ereise (14) Solution,transportation,and Precipitation of Iron and fiilic»-on.3e o1 . ,Vo1 . aXIV,£o .3 ,1929 -Moore and ifaynard (15) ticonomic Geology -So.18,1923,p.528,-Lovering (16) Data of Geochemistry -tf.S.G.S. ,Bull .770 ,1924 ,p . 110-111 -Clarke (17} Zeit .Prakt .5eol . ,1910 ,p .356 - Ssiss (13) Economic Geology ~ Ho.l7,1922,pp.422-436— GRANER (19) Dictionary of Applied Chemistry - Vol.VI ,p .249 -ffiiorpe (20) U .S .G .S . ,Sono .52 ,p .521 - Van Hise and Leith • - ''•.:• 68 . (£1) Ths Hydrous Oxides - McGraw-Hill, 1926 ,p.34 -Weiser (22) Mineral Deposits -ScSraw - H i l l ,1928,p.363 -Lindgren (23) Bocks .Rock-Weathering, and Soils - aacmillan,1921 ,p. 166,-Merrill (24) Quart.Jour.Geo1.Soc.London,1889,7o1.XL?, -Johnstone (25) Origin and Color of lied 3eds - Jour.Geol.,?o 1 .XXXI?,So.2,Feb-ilar, 1926 —Dorsey (26)She Hydrous Oxides —McSraw~Hill,1926 —V/eiser (27)Origin and Color of Bed Seds -Jour.Geol.,Vol.X£XVI,Eo.2,Feb-aar, 1926,—Dorsey (2S) Climate and Serrestial Deposits - Jour.Geol. ,?O1.A?I,ISTO.3, April-lay ,1906 ,p.296-Bari'ell (29) Clays,Occurrences.Properties,and Uses - John Wiley and Sons,1927 - Hies' (30) Bauxite ana Aluminium - Imperial Institute,1925,p.10- Bumbo Id (31) On the Constitution,Origin,and Dehydration of Laterite — Geol. ISag. , 1903,p.63. — Holland (32) Mississippi State Geol.Survey - Bull.19,1923 ,p .l - Morse (33) The Hydrous Oxides - 2c&raw-Hill,1926 - Weiser (34) Data of Geochemistry - U.S.G.S.,Bull.770,I924,p344,-Clarke (35) 2hin-Bectioa liineralogy - Sb&rac? - Hill ,1933, p. 176 -Bogers and Kerr (36) The ICaolin Minerals - U.S .G.S . ,Prof .Paper 165-3,1951 -Boss and Kerr (37) Halloysite and Allophane - U.S.3.S. ,Prof.Paper 165-G,1933 -loss and Kerr (38) Clays,Occurrencea,Properties,and Uses - John Wiley and Sons -1927; - Eies (39)Origin of Kaolin - Econ.Geology ,X , 1915,pp.8S-93 -Lindgren (40) Hxe Kaolin Minerals - U.S.G.S. ,Prof.Paper 165-£,1931mp.l73 -Boss and Kerr (41) The .Kaolin Minerals -tf.S.G.S.,Prof.Paper 165-s£ ,1951,p.174 -•Boss and iferr - -- • -. 69 .••-• (4-2) Halloysite and Allophane - U.S.G.S.,Prof.Paper 185-G.1934 -Boss and lEerr 9 {43) Clays,Occurrences,Properties and Oses - John Wiley and Sons .. 1927,- Bies (44)Bain-Section Mineralogy — nfcGrav, - Hill,1933»p.l91 - Eogers and Xerr (45)A Descriptive Petrography of Igneous Boclcs -Vol.II,Univ.of Chicago Press 1932,p. 144 - Johannsen (46)She Action of Certain Alkaline Solutions on Felspar and Hornblende -Jour. Geol. XXIV ,1916,pp.191-196 -Stephenson (47) Thin-Section Mineralogy - 2fc&raw-€ill,1933,—Hogers and Kerr (48)On the Process by which a Felspar is converted into Scapolite -Silneralog. ,VIII ,1889 ,pp. 186-196 — Judd (49) A Treatise on 3etaniorphism - tJ.S.G.S. .2on.ZLVII,1904,p.340-Van Hise (50) A Descriptive Petrography of Igneous Bocks - Univ. of Chicago Press ,Vol .II ,p .199 - Johannsen (51) Corundum, Its Alteration and Associated Minerals - Proo.Am.Phil.Soc. XIII,1S73,pp.361-406 — Senth (52) Studies on the Alkalinity of Sea® Silicate Minerals -Prof .Paper 185-A ,1934,—Stevens 9 (54)A Descriptive Petrography of Igneous Bocks - Univ.of Chicago Press 1932,Vol.II ,p.209 — Johannsen (55) Bocks0Bock-i7eathering and Soils - Macmillan„192l, — Sferrill In the Preparation of this chapter a number of other works were consulted,without being directly referred to at any piaoe in the text. The Host Important of these are given below. x'he Processes of feathering (l)Bocks,Bock^eathering,and Soils - Saemillan ,1321, — iferrlll (2) 25etamorphic Geology -Henry Holt and Co.,1915 — Leith and Mead (3)Data of Geochemistry - U.S.C-.S. ,3ull.770,1924 - Clarke (4)Bhysico-Cheraical Geology - - Bastall 100 (5) College Physiography — i t a i l l a n ,1915 — Tarr and Sartin (6) Origin and Hature of Soils — Twelfth Annual Hept. ,U .S*0 .S . ,pt .l 1891 (7)Weathered Zones of the Drift Sheets of Illinois — Jour.Geol, Vol .XXX7I I I ,Bo .1 , 1930Leighton and KacOlintock and other references a&ntioned in the text. Colloids and Colloidal Phenomena The works consulted in the preparation, of this section were the following: (lifftae Colloid Hatter of Clay and Its i&asurensnt - 0.SVG.S.?3ull.368 ,1909 — Ashley (2physical Chemistry for Colleges - McGraw-Hill ,1926, ~ Millard (3j She theory and Application of Colloid Behaviour - 3cGraw-Hill,1924 Chap.XVIII - Lindgren * * {4}?he Bole of Colloidal Solutions in the Formation of Mineral Deposits-"?rans«Inst.2Iin.3;- afet. .Dec. 1924, — Boydell [ b ) T h e Ministry of Colloids - John Wiley and Sons, 1917 —Zsigaondy [6)ThQ Bole of Hydrolysis in Geological Chemistry - Scon.Geol..Vol.6 1911 — Wells " * (7)Solution,transportation,and Precipitation of Iron nad Silica-Scon. Geology ,7o 1 . IJiVI,I\ro .3,1929 Moore and IMynard (e)Sata of Geochemistry - U.S.G.S. ,Bull.770,1924 — Clarke {9}5he. Hydrous Gzides - McGraw-Hill ,1926 — Weiser (lO)Mineralogical Characteristics of Clays —Scon.Geology,X,1915 -Fry Other specific references are fotmd in the text. Weathering Processes " •Book-Seattlering,and Soils s,rby Serri 11,"Physico-Chemical Geology" b y tall,and the "Hydrous Oxides of weiser.proved the most useful works consulted in the preparation of this section,as wall as those referred to specifically. 71 • In general the references given in the body of the'text .explain the source of the remaining material presented in this chapter*It might be .men-tioned that th& two recent publications "The Kaolin !Ilserals«%afid "Halloy-site and A1 lophane",*J.S,a.S. ,Prof.Papers 1 S & % and 185-0.(1931 and 1933} by Boss and i£errtas well as the text-book " Thin-Section Mineralogy", by Eogers and Kerr* OHAPgBK TuO 3B0E30AL gdSATHSHIHS : -L&smims AM BA0XI2SS ; [j ] •!] ' ' ' .1 I 100 Introdtiction In tropical and sab-tropical regions,the processes of rock decay are usually carried further than is commonly the case in temperate climates. Leaching is more complete,the silicates are sore thoroughly decomposed, ' and the residues are richer in hydroxides.In fact,"tropical" weathering tends to produce an end -product rich in ferric hydroxides and aluminous . hydroxides,as opposed to one in which aluminous hydrate! silicates pred-ominate resultant upon "temperate" weathering. Although in many cases the result of weathering under tropical con-ditons is apparently similar to that experienced by the rocks of the more temperate regions,in general when decomposition has progressed far enough the residues have a similar composition and form,and are usually classed under the head of "Laterites and Bauxites".0!hese represent an indefinite mixture of aluminous and ferric hydroxides,with possibly quartz,and minor quantities of other minerals. It Is usually assumed that decomposing forces are more active in the. warmer regions of the earth.if by this is meant that chemical action is more powerful,it is undoubtedly true,but It is questionable whether the reduction of a rock to its various components Is effected more readily in this case than when the rocte is subjected to the weathering processes of a temperate clime.In the latter case mechanical action plays a more imp-ortant role,mainly by frost-action,and so by producing a pulverulent structure in the rock,exposes larger surfaces to the action of those for-ces which are present. The work of a great .number of observers has shown that the process of disintegration is sore active in the higher latitudes.However it seems to bs tils case that actual decay is more active in -warm regions where there is abundant rainfall. Irrespective of the relative velocities of weathering in temperate and tropical cliaates.it is a fact that the intensity of chemical action Is enhanced by the latter environment.resulting in the formation of a more advanced set of "end-produets".ihe term "latc=rization" is reserved to cover these processes in a broad sense. xhe present chapter is an attempt to summarize the available literature on tropical weathering and its effects le.laterites and lateritiaatiOB. Although not essentially a product of this type of decomposition.a section on kaolin and its origin is also included. 100 •: 74 • Lateri te: .Definition and Glassif ication Laterites hare long been a subject of interest and speculation to geological workers in tropical climates.After even a cursory examination of the literature,however,one is immediately impressed by the looseness of definition that has prevailed,as well as soma of the interesting,if somewhat imaginative theories which have been advanced to expMin their formation.In view of the interest attached to this subject,it is felt that a rather detailed resume of the earlier work on the subject will not be .amiss. At present laterite is generally reserved for those residual deposits consisting essentially of hydrous oxides of aluminium and iron. Bauxite is a variety of laterite in which the proportion of hydrous alum-inium oxide is high enough to permit of the commsrcisl extraction of alum-inium. -The earliest reference to laterites is that of Mr.Francis ,Buchanan* in a description of his travels through Malabar,Kansra,and the Mysore territories of Southern India in 1807. * A Journey from Madras through the C^mitrTss of Kysore , 0 a n a r a ^ d Mal-abar rr^J^oMon...1607. Yo 1.1 i . pp. 436-437 —F.Buchanan :. 3© says "what I have called indurated clay is not the material so called b,y iar».£irv7an,who has not doscribed this of which I am writing.lt seems to be the Argil la lanidae of w'allerinsl,andis one of the most valuable materials for building.lt is diffused in immsns masses,without any appear-ance of stratification,and is placed over the granite which forms tho basi s of -iialayala.lt is full of cavities and pores,and contains a very large proportion of iron in the form of red and yellow ochres.In the • ' '.75 • • . mass,while excluded from the air,it is so-Soft,that.any iron instrument readily cuts it,and is dug up in square masses xvitha pickaxe,and i'mmed-iately cut into the shape wanted with a ,tvowel,or large icnife,It very soon after hecones hard as a brick,and resists the air and water much better than any bric&s that 1 have seen in India.1 have never observed any animal • or vegetable exuvia contained in it,but I have heard that such have been found,- in its substance .As it is usually cut into the form of bricks for building,in several of the native dialects it is called"brick-stone"(Itaca Cullu).Where.however,by the cashing away of the soil,it has been exposed to the air,and has hardened into a rock,its color becomes black,and its pores and inequalities give it a kind, of resemblance to the skin of a person aff-ected with cutaneous disordersjhence in the Samil language it is called 'Shuri-cull' or itch-stone.The most proper English nan© would be laterite .form Lateritis.the appelation that may be given to it in science." The name laterite has been extended to cover a similar -looking mat-erial In all parts of the world - India,the Straits Settlements,Java,Victor-ia and Ives tern Australia,South Africa, the Soudan,Sierra Leone and the Congo Territories,Brazil,and elsewhere. j As Fermor8 points out however rocks of more than one origin are includ- j ed under the term laterite ,and as this fact Is not always recognized,diver- | gent theories have been invented to explain dissimilar occurrences.Since the , usage of the term laterite has been so loose,fermor prefers not to restrict ;. it to only the material possessing the properties described by £uchanan,but rather by the use of suitable modifying' adjectives to extend its application !,' to ail deposits high in hydrous oxides of alumiuis and iron,usually resultant upon tropical weathering processes. 100 V.aat Is Laterite - Seoi.l^r. .1911 .P .4M --^rmr IB India laterite Has been most carefully studied and in general two types described;"high-level" and "low-level".The tmrmr is reserved f o r those deposits whieh have apparently been formed en situ .while the latter is used for those which Have obviously been transported. The classification of Pernor is given below in tabulate form/. t ' a - < --. . ,-J37 UfX * * Jc JUT r JT ifc'n. t&jr '«n / r OAS/C Jis/Awm,y/t . AQC/f « f laftr/fr 1 /nts? Ore | AC/0 /TOC/f 1 | leferfr/e puDrfftj* 4 s I 1 > i | N ! •I i t 1 \ 1 •tf/Sceauf toA* ioferr/ta * N 1 > i i D i tk a . . > \ fi » r >• "->V >.' J/fS Fcfo - 'j V ptsarf^oje Strfc/S/e UfkttfMJ /wf/f J Figure b. The term bauxite was first used by 3erthier%ia 1821,in describing a cert-ain bed of non-plastic material in the vicinity of Lee 3aux,in Provence.This deposit.always considered to be clay .proved on analysis to contain no silica in any form,but to consist of only hydrous oxides of aluminium and iron. * Ann.de s iiUes -volvi .1621. «p. as l-&..<; -To this remaricabie clay-like substance was ^iven tne name Bauxite .after the locality from t&iiich the fisst sample v*as obtained. The essential similarity of bauxite and laterite,and their characteriz-ation by free hyurated alumina.-ftas first recognized by Bauer*,and amplified _* Jahrbnca. fur tin..1696.vol.il.pp.IVl-Zli —3auer # 100 by Holland'1 fleol.Hag. - 1903.p.59 - Holland In speaking of the work of Bauer and Holland .referred to above,Fo*« gives an excellent summary of the question,part of which is reproduced below. Bauxite - Crosby.I.ockwood and r ^ ,i927.n.3 - n ^ T T T T l ^ " Subsequent sork ha., amply confirmed the previous investigations,but there i s a tendency to-day to regard the highly ferruginous varieties,chiefly cousi-stx^of the ferric hydroxides Imown as limonite and xanth0siderite,as laterite,and the highly luminous varieties.composed largely of those colloid-al hydroxides of aluminium .hich give an analysis roughly equal to a mixture of gibbsite end diaspore,as bauxite .However ,in aost cases, the mixtures of ftrrie hydroxides and aluminium hydroxides a,e present in colloidal form and not as minerals j, and the designations,bauxite and laterite, therefore require considerable modification in meaning." rtAS a g e n e r a l r U i e > U i s satisfactory to speak of aluminous laterit-es,laterite,and ferruginous laterite,according as the samples are obviously aluminous,doubtfully mi*ed,or clearly ferruginous,and until a chemical anal-ysis has been made to supplement the physical characteristics." "The variable composition of pr iory laterite,therefore ,depends largely on the relative proportions of the t*o lateritic constituents,the hydroxides of ferric iron and aluminium usually present in colloidal form.Shen these constituents are present in about equal amounts,eg. 50% hydrated ferric oxide and 50;t tri-hydrate of aluminium,the substance would approzimate a true later-ite m composition.If the ferruginous component exceeds m % ,the rock rould constitute an iron ore of the liaonitic class( or of a hematitic variety if denydration,which is not unusuul,had taken place).On the other hand,if the 100 aluminous percentage is in excess of 50%,the rock would constitute an alum-inium ore of the bauxite class.If it were sufficiently free of impurities, chiefly silica,and suitable for the extraction of .aluminium it could def-initely be called bauxite." Eie term bauxite has been used by many writers to demote a mineral spe-cies.In view of the resulting confusion it seems much wiser to restrict the use of bauxite to aluminous laterite,as suggested by Fox,in the above para-graoft. & Physical Qheracter of Laterites An excellent description of the physical occurrence and properties of laterite is to be found in "Bauxite" by Fox%the following quotation being taken directly from this work. ,Lockwood and Sons. 1927 .p.56 -Qvril S.For. "Since two ar more of the hydroxides of (ferric}- iron and aluminium are present,and can occur in variable amounts of each kind,it is evident that the specific gravity and hardness of the bauxite (laterite) will vary accordingly. So also will the color.Lateritic bauxites of primary (residual) origin have a minute cellular structure,whereas bauxite of the "terra-rosa" type are of-ten as fine-textured and irapersious as clays, although pisolltic varieties of either amy be indistinguishable from one enother.lt is evident that bauxites Cai1 n o t h a v e a definite melting temperature.The water of constitution in bauxites varies from less than 10% to over Z0%. If subjected to heat this wat-er is driven off - usually in an irregular manner - there being large emissio-ns at about 250 degrees G. and again at 700 degrees G. "1-he less water there Is in bauxite the greater is its hardness and 100 specific gravity.The massive lateritic bauxites are often used for build-ing purposes in tropical climates/out the crushing strength of the material is low and the resistance to abrasion weak." , < T h e m o s t is tic features of most bauxites are their variegated colors {red.varying from pinkish-cream through chocolate to dark red) and their pisolitic texturea.Shis is particularly true in the case of lateritic bauxites.but in the type provisionally regarded as " terra rosa-.the texture is generally finely granular and impervious.unless a pisolitic texture has aeveloped.Exposed outcrops of lateritic bauxite generally have a pitted sur-faced coriaceous aspect.suggestive of volcanic rock may also occur.On a gentle or level ground the bauxite surface may be smooth.and the rock itself broken up into a kind of pavement.In the Joints and cracks of this nave •mil trees and shrubs often find sufficient soil for their existence. So re normally the surface of a lateritic plateau has a thin cover of red to yel-low clay on which t&e grass grows freely.In regions of heavy rainfall the lateritic bauxite may be rough and bare,the surface of the rock being of-ten black with a metallic glaze,thereby increasing its resemblance to a dark scoriaceous lava." "In scarps and c l i f f sections.where great masses have become detached,the Material shows a vesicular to vermicular texture and presents a mottled appearance.?he small cavities,fissures,and tortuous tubes in the rock are irregular,and generally have no obvious directional arr&ngpnrat.&oaetloBa they are horizontal and sometimes vertical.The mass of the material gener-ally looks ferruginous,the tubes are often lines with a limonitic glaze.and where not previously weathered,filled with cream colored,powdery aluminous laterite,or gibbsits." 100 A common property of some laterltic bauxites is their tendency to harden on exposure to the air.She explanation lively rests in their high water content.hardening being due to partial dehydastion. Another peculiarity of aany laterites is their opacity for reconsolid-ation.Debris from a laterite scarp which accumulates on the slopes or in the valley below,frequently beeoaes cemented in*o a solid mass,resembling the original m a t e r i a l s the scarp.fhis power of agglomeration is evidently stronger in highly aluminous laterites than in the ferruginous varieties, as a result,any lateritic debris.exposed to the wash of the rains and the scorching heat of the sun,will be subjected to a natural concentrating action.whereby the ferruginous matter will be separated from the highly aluminous .material,, ^iMral-Q-SlC. Constituents of Laterites Quoting Fox* .Bauxite -- Crosby.Itocirwood and Sons .1927 .u.42 — Cyril S« * A microscopic examination has revealed crystalline gibbsite in many thin sections of Indian bauxite and laterite.The mineral was commoner in the pisolitic varieties of both the bauxitic and ferruginous types and vase consistently present In the pisolitic laterites.Many of the pisolites were veined with nests and patches of crystalline gibbsite.Eo other recognizable mineral was detected.The same negative results as regards the presence of other possible minerals.eg.diaepore .etc.,with the possible exception of xanthosiderite,has attended the investigations of other observers when working with American and European bauxites." Pisolites generally exhibit a concentric structure,the centre consist-' -v.- • • . 81 ing of either earthy matter or dark ferruginous material. She presence of diaspore has been glibly inferred by many of the ear-lier workers without any mineralogic proof. iforse*,for instance.describes three definite hydrates of alumina from the Hississippian depositsidiaspore (A1P0^.H?0) .the di-hydrste (AUQ~.2fl«.0) and gibbsite (A^Og.SHgO). " Mississippi State Geo!'.Survey - Bull.19 .1922 -p.l — aiorse Hollsndtfrom an examination of the analyses of Indian later!tes says that detrital laterite shows a higher proportion of diaspore,than the residual type. * ,1 -3gfli.«lfeg*..«19Q& .P . 59 ~ Holland Eo definite evidence of the presence of diaspore in deposits of this type has so far been obtained,either under the microscope or by the use of hemj solutions.(Diaspore has a specific gravity of 5.3 - 3 . 6 } . On the other hand it is usually described in mineralogical texts*as being a ooaraon associate of corundum,and originating from anamorphic action or hydrothermal processes. Descriptive Mineralogy - John wiley and Sons ,1926 ,p.431 - Dana and JghiB-Seetion Mineralogy — McSraw -Hill .1953 .p.176 - Rogers and Kerr 3?he subject will be treated again under the head of chemical properties. . Chemical Character of Laterites The following are the most common aonstituents of laterites; (1} Aluminium hydroxide- the essential component, possibly as two colloid-al forms and as crystalline gibbsite. (2) Ferric hydroxides - probably present as two colloid forms arid perhaps • ' • - ' 82 a crystalline form as xaathosiderite. (S) Ferric oxide - is recognisable as hematite in certain dehydrated laterites.Ferrous oxide and hydrate have never been found to be present in -bauxite. {4} Silica - is a frequent insoluble impurity in the from of quarts,but is probably more frequently present in small percentages as hydrous alumino silicate,and rarely perhaps as secondary colloidal silica. (5) Titanium -present either as the dioxide or hydrated oxide,end forms a conspicuous impurity in lateritic bauxites which have been formed from basaltic rocks. (6) Manganese - occurs as psiloaalane or pyrolusite.Kas been found-in ferruginous laterites but is rare in rich bauxite. (7) Lime- generally occurs as the- carbonate,frequently present in very small amounts,and so also is magnesia,which is more common than lias. (Potash and soda- rare constituents in bauxite but detectable in traces in some argillaceous varieties of laterite. (9) Chromium and Vanadium-have been detected in the lateritic bauxites of some localities; so also has zirconium. (10) Sulfur and phosphorous - often present (11) &old, tins tone .copper,diamonds,nickel,cobalt and other e l e c t s and metallic oxides,often in payable quantities,have been found In laterite un-der special conditions. T h o proportion of alumina in a bauxite gives some indication of the de*-r e e 0 f lateriaation,and the greater the percentage of combined silica,the lesser has been the lateritic action.The whole question of composition dep-enus on the process of* formation and on the constituents in the original rocs.In detrital and certain replacement laterites.there are obviously imp-83 • uritios,which either have been introduced, or could not be assimilated at the time of development. As Fox* points outs Bauxite - Crosby,Lockwood and Sons . 1 9 2 7 - .p.49 — C y r i l BuFox. " The composition of the original rock from which laterite has resulted can often be traced In the constituents of the laterite.in India the later-ite over certain basalts is highly titaniferous,and it is laiovm that the basalts contain appreciable amounts of titaxiia.In Cuba a ferruginous later-ite forrsed from a serpentinized periaotite contains detectable amounts of nickel and cobalt.In the Gold Coast some of the bauxites contain gold,due to.the laterization of rocks carrying stringers of gold-bearing quartz.Tin-stone is found in certain latecitos in Eigeria.fl It is obvious that no rock,unless it contains the lateritic constituents alumina and ferric iron,can be laterised.lt Is therefore evident that sandato stones,quartwites,linestones and dolomites cannot be so affected.If they con-tain feisp&thic constituents and ether aluminous or ferruginous minerals,an impure variety of laterite may result,and "terra-rosa" n?ay be formed from impure carbonaceous rocks. The following table,after Fox*.illustrates the proportions of latsritic constituents in a number of common rocks form which laterite may be formed if the texture of the altered rock Is sufficiently porous. Bock Average % of Pe.oO'x Total lateritic const. % SiC^ Uranite family 17 3 20 65-75 Trachyte-Syenite 20 4 24 55-66 Andesite-Diorite 18 6 24 50-65 Kepheline-Phonolito 23 3 26 40-60 Anorthos.ite . 2 5 1 26 60 Basalt-Dolerite 17 6 25 48-54 Peridot its 5 10 15 30-48 100 Sea.Bocks ^AigOg F^Cg Sotal later H ie % o f S i C . compounds 1 ~~ K Phyllite 23 Slate 23 Mica Schist 24 Basic Gneiss 18 10 £8 Granite Gneiss 20 2 SO 6 0 55 6 30 55 SO Aluminous shale 40 3 22 70 Brick Clay 50 7 Fire clay si i Ses&dual Clay 12-33 s-x 18-34 43 37 45 32 50 3 0 - 70 4 6 Kaolinite 39 From the above it is evident that syenite,phonolite,and anorthosite are highest in aluaina among the igneous rocks.Aluminous shale,and in fact almost all clays,contain more alumina than the igneous rocks,but they have ,as a rule,an impervious texture. Alumina The results of heating bauxite gradually to higher and higher temper-atures, and noticing the evolution of water of combination,has led to the belief that the alumina most fe present in at least three forms- crystall-ine gibbsite,and two colloidal hydroxides.Crystalline gibbsite is a common constituent in the matrix of pisolitic bauxites,as has frequently been ob-served under the microscope. As mentioned before the presence of diaspore was usually conceded by earlier investigators.Holland * points out that detrital laterite is usually less hydrous than residual,and. explains this fact by the passing over of gibbsite In'-o diaspore through natural dehydrating processes. Jjj*eol«2fea« .1305 —Holland As Weiser* points out there is a gradual transformation from an amorph-ous to a crystalline oxids during the ageing of an aluaina gel.Eewly formed gels consist solely of anhydrous AigCg and adsorbed water.On long standing tho gels go over to Van Be rams Ian1 s unstable tri-hydrate, which appears dis-I.. . : ' . . - • 85 tinct from the crystalline trihydrate.fe know however that gelatinous alum-ina,aged in the presence of alkali,giveb tri-hydrate crystals identical with gibbsite. • She gydrous ..Oxides - BcSraw-Hill.1926 .p.107 — Weisgg Clarke® likewise emphasises the fact that only the tri-hydrate is thrown down as a definite corapund tfitoa solutions of sodium aluminate ,\vhen decomp-osed by COg in the laboratory. * Data of Geochemistry -g.S.a.S. «3ull 770.1924.x).£01 -Clarke In view of the above work,augmented by that of many other workers,it would seem likely that the crystalline tri-hydrate,gibbsite,is the only definite mineral species found as a result of weathering processes,the reg-aining alumina being present in either gel form with adsorbed water,or in some hydrated stage in its transformation to the crystalline tri-hydrate. The ''mineral" commonly described as bauxite is an indefinite hydrate of aluminium oxide or a colloidal gel with adsorbed water to which the term "cliachite" is often applied. There is however a tendency of the alumina gel to lose water with ageing, which would explain tho fact,pointed out by Holland,of detrital laterite being less hydrous than residual. As pointed out by Pox* if the- alumina in bauxite exists in a colloid form ,it will Impart the properties of a semi-permeable nembrane to the zone in which it is present.Consequently no colloidal silica and no ferric gel will be able to pass through such a zone,although ferric and other salts may read- j ily negotiate such a membrane. '{ *. Bauxite - Crosby.Lockwood and Sons .1927 - p.59 - Fox . :,j This aspect of the condition of the alumina in laterite is thought to be •'.,.."..'• •••• ; ' ' i.tt •:•;<• ' : . .. :.|h 100 of considerable importance,for ,should a condition of dialysis become estab-lished,as it would appear it must do,then powerful capillary forces will be-COKB available,and chemical separations will be induced,both as aresjalt of o osmotic pressure and by the migration of electrically charged sols in the electrolyte (the acid or alkaline ground water).The hydro-gel of alumina is thought to be less active than that of ferric iron (positive) or silica (neg-ative) and evidently remains stationary in the mass of the laterite.However unable it may be to control the movement of mineral salts,this colloidal al-umina probably exerts a strong retarding influence on the migration of other colloidal particles. With regard to the pisolites or oolites so conmon in bauxite, lb x* has the following to say; "The pisolites themselves nay be cemented together in a hard matrix,or the-se pellets,often more than 2" in diameter,may lie in a soft powdery mass.In the fornssr case the matrix is often found to be crystalline gibbsite.In both cases the pisolites have an amorphous texture,with frequently a concentric structure.Shere is little doubt but that this pisolitic structure occurs only close to the surface,at or a little ab^ve the height of the ground-water level.There Is also no doubt whatsoever that some alumina must be carried in solution by seepage waters,because it is not uncommon to find pisolites coat-ed with aluaiim hydroxides which are highly ferruginous within.The opposite structure of a pisolite is more frequently encountered,showing that ferric hydroxide is frequently deposited on an aluminous pisolite.In both cases of 1 loose pisolites there is thus evidence of deposition and accretionary growth, hut this explanation will not do for the pisolitic structure of hard raassive bauxite.In this latter case accretiocary action is thought to be subordinated 100 by some selective action as a result of Liesegang phenomena.*' * Bauxite — Crosby.Loctoooa and Sons . ,1927~I~p.60 — Fox fferric Oxide Ferric oxide appears to be closely related to and almost invariably present with alumina in laterites.lt is almost invariably present in an amorphous hydrous form,roost probably colloidal in nature.In the sol form it has a similar positive charge to the hydrosol of alumina,and the two wotM tend to keep apart,possibly explaining the peculiar mottled effect so common in sone laterites.As was emphasized in the previous chapter,there appears little evidence to support the existence of a series of definite hydrates of ferric oxide.Hematite has been definitely recognized,but the term limonite has served as a general appelation for all brownish iron hyd-roxides.This understanding of the term is useful and logical and will.be retained in this paper. Here,as with hydrous aluminium oxide,there is a tendency to dehydration with ageing,but conditioned by temperature,humidity etc. Has tall* substantiates the above usage for,flimonite"9and emphasizes its colloidal origin,even suggesting a similar origin for the crystalline mono-hydra te,gothite, .LPhysiCQ-0hemleai Geology.--Arnold.1927 .p.241 — Rastall In connection with the concentration of ferric oxide at the surface,so comaon in lateritic deposits,Fox* says* "It is thought that this concentration is effected by capillary action »ia spite of the fact that,theoretically,it should not do so as s colloid in concentrated form.lt is known,however,that as a colloidal gel this sub-stance behaces differently according to its degree of concentration." • ' ,••.•-•.•• - . .. •.• 88 He discusses the action of capillarity upon positive and negative sols ,and shows that negatively charged colloids in dilute solution behave sim-ilarly to positive sols.He continuesj "As a crystalloid(salt) the ferric hydroxide would be unaffected by the above considerations.It could be precipitated from solution in various ways by suitable reagents,or sore)times by bacteria . bacteria could not flour-ish on the scorched bare surface of a laterite region during the dry monsoon, however suitable Bay be the climatic conditions during the wet season.Never-theless,the presence of nodular agglomerated masses of pisolitic liaonite in the cairasse de f&$_zone of a lateritic mantle suggests that ferric hydrox-ide Is being deposited by percolating waters or under the influence of capill-arity -probably both processes work at different seasons." Bauxite - Crosby.Lockwood and Sons ,19£7 -dp.61-62 —Fox The predominant red /brownish red and pink tints ,so common in laterite and bauxite are suggestive of the ferric iron being reduced to the anhydrous oxide ,or at least a highly dehydrated conditon.Yellow and other yellowish tints are less evident in laterites and rare in bauxites, ' .Silica The removal of silica during rock-decopposition is probably the most characteristic feature in the chemistry of laterisation.Pree silica is a not Uncommon impurity in laterite foiled from rocks containing free silica as quartz,eg.granite,gneiss,etc.,but it is an exceedingly rare copponent of a primary laterite forced iron basic rocks such as basalts and. dolerites.Silica (quartz) is cozaaon in secondary or detrital laterites,and as secondary silica in sosaa primary laterites.In the latter case there is nsually eveidence of the region having undergone submergence as a result of which the laterite has 100 been covered by deposits of sediaentary material,as is the case In 30:02 of the British Guiana occurrences. Ths removal of silica from the breaking down of mineral silicates is a simpler process,since this silica is usually in soluble fornj.lt is the considered opinion of many investigators that rock decomposition leads to the production of gels or mixtures of gels.'These colloids are not aoorphous alumino silicates,but simple gels ,poBsibly mixed,due to the mutual precip-itation of positive and negative soIs.The acceptance of suea an explanation removes the difficulty of trying to account for the disintegration of hyd-rated silicates,or the so-called second si-age in the production of hydrox-ides from original silicates.it; is evidently a single process,but complicat-ed by the fact that the colloidal hydroxides carry electrical charges,and,if given freedom of iaovo<Bsnt,say as sols,migration of the colloids con be caused by the production of a difference of potential. " l»lthomarae The following quotation .describing the lithocaarge zone which almost Invariably accompanies bauxite deposits,is fro 31 " 3ami te"* by Fox. *._Bauxite , Crosby. LocKwood. and ->- • -"The silica in,or associated with,bauxite or laterite Is usually in a state of combination.The lithomarge zone beneath the laterite(in many cases) probably represents the aanner of combination;in this aone,however, siliceous bands of ferruginous matter are also eoa}faon.Fro«i field observations,the.e is little doubt of the genetic relationship between the bauxite(1,see J&slg&es) the lithomarge ill and 111) and the kaoliniied trap (IV) . L II. I l l IV Si02 0 .80^ 42.79£ 40.97£ 37.31JS 100 9.06$ 6.44/j 3.33JS 64.77$ £3.96?. 22.97^ 27. -^2% 0.3i>; 13.4l£ 17.41$ %£> trace l.£4# £ .00$ 0.76;? > 14.73J& 14.77$ 13«40£ analyses of the bauxite stand In striking contrast to fas iithosurge a •few imt feelo®** / lithoaarge aone is fount la almost every occurrence of laterite .-whether it be on the 3arling Sango of Is stern i>ua trails, tho frowning scarps of Pan-hala Fort in the Deccan of India.the fsrest-covered slopes of the Vogolsberg in Germany,or the coastal region of Britsih Suiana.Shere Is no question as to any doubt about tho gone tic relationship between the overlying laterite.the lithomarge.and the underlying altered roofc." • • it is interesting to not© that,wherever studied,tho watar held in a state of combination in bauxites behaves as though it were a part of a def-inite compound.Shis water coaas away at definite teaEgera.tnres.and not gri«I» ually,a3 one might erpect from a purely colloidal substance.In general it would appear that there are two definite points.260 deg.3. and 700 Seg^C., at wnich largo volurnss of water given off.She first agrees very wall with the destruction temperature of gibbsite,but of the other,the larg-ar evolution of water,no thing is tenos-n.Srhe ferruginous laterites behave in a normal manner,and have not shown any characteristic features. 100 TYplcal Occurrences A few specific descriptions of tropic weathering from various localit-ies are included.In general all true laterites are associated with a tropic-al climate.the deposits of the (Jnited State s.France .Hungary ,e tc. be ing formed in the tropical 'iartiary climate.Cameron and Snow*.in an examination of sev-eral thousand soils from all parts of the United States.discovered hydroxide of aluminium in but on sample. *_Bull.30.U.S.Bureau of Soils .Sept. of Agriculture .1905 -Cameron and Snow The accompanying maps are reproduced from "Bauxite",Crosby,Lockwood and Sons,1927, by Cyril S. Pox,and illustrate known occurrences of bauxite with commercial possibilities. Laterization in Sieera Leone * —(See map 1) _GeoI.Mag..vol.LVII.Ko.7.1920.p.213 —Dixev The rock affected by feathering is here a medium-grained norite.Due to tho rapid, erosion,induced by nigh relief,the laterite formed en situ is ma-able to accumulate to any depth.A covering of only a few inches is found on hill sides,while in the valleys deposits several hundred feet in thickness occur. » tfhere examined,laterization hid proceeded along joint planes until only cores of unaltered material renained,which were surrounded by mos?© or less concentric layers of red laterite,becoming more irregular in shape outwards. It is thus possible to trace the change from unaltered norite to the outer zone of red-brown laterite. Felspar is the first mineral to bs affected.It changes to a white opaque alteration product,which spreads along cleavage cracks,and for a time leaves flakes unaltered,then a clear white recrystallization sets up along old i l l ? 1 100 old cleavage cracks and remaining parts of the crystal dissolve out Result-ing a framework of parallel plates studded with minute colorless crystals (probably gibbsite).Later iron staining commences and the pseudomorph grad-ually breaks down. Diallage changes from almost bleck to brown at a very early stage and with the rhombic pyroxene causes a mottlifg of the light colored halo.It is grad-ually pseudomorphea in fine brown scales with an earthy last re. The rhombic pyroxene develops a close platy structure and retains its bronze lustre to a late stage.Iron ore is recognisable and apparently unaltered long after all other minerals have disappeared.01ivine. is not recognisable after later-ization has commenced. Sons granitic rocks occur in the area and are likewise affected by weather-ing. He re the rocks are broken down into small masses b;; weathering at the surface .the decomposition proceeding inward and forming generally a white kaolinized shell .which breaks up later and becomes increasingly stained b;/ the destruction of iron ores and ferro-magnesian minerals*Ihe final product is a great thickness of red-orov.'n lateritic clay. Low grade bauxite deposits have been reported from Sierra Leone5an analy-sis^of the typical material being as follows: Al^Og ' 51.03/i PegOg 10.14/i •SlOo ; 9 . 46$ HgO^ ' 29 ,32$ * Imp. Inst. Bui 1.1925 —Bauxite and Aluminium .p.63 •—Bumbo Id ..._ For further information on t£is region the comprehensive paper of J.2J. Campbell* should be consulted. * Observations on the Laterite of Sest Africa-i'rans. Inst.Min.Met. ,volxix» **** 1910.pp.£32-457 - Campbell 100 Bhodesian Late rite * {see .nap 1) * G-eol.Maff. «?ol.vi,1909., n.550 - aanaliT Laterite is the most sbimdant superficial deposit in Kg.odesia.The climate here is fairly dry,but the average rainfall(26"J is restricted to a period extending froa the middle of October to the middle of April. The laterite appears to be largely associated with drained swamps, and is independent of underlying rocks,although likely detrital where It overlies defittentai-y ones.iilsewher it is found situ and reflects the co;rrposition of its parent rock.She laterite is normally congloosaritic due to the inclus-ion of vein quartz,and underlying rocks,as well as drifted sand. Its composition is typified by three analyses given below; 14.71> 32.14/5 34.8;i A l 2 0 3 1.41% .22% 25.9% HsO 4«44'/& 6. Insol.(withSiOg) 75.10% 60.63% 29.2% Laterite in Western Australia * (see map 2) She laterites of Western Australia are divided into (1 jPricnary laterite and (2) Secondary laterite.The priaary laterite is a product of tile norm-al processes of weathering,accompanied by abnormal conditions o f rainfall and denudation .Hero laterite is no L necessarily tropical ,icu32nse deposits in Western Australia being extra-tropical,but is simply associated with rocks of suitable composition.Ihe climate Is one o f alternate dessication and saturation.In general short or long periods when the rocxs are saturated •alternating with long dry and hot periods when they are completely dessic-ated,seems to favor the production o f laterite. . * Seol.Mag. .1912.p.399 Simpson : 100 In Australia the deposits are usually found from 500 to 1500 feet ab-ove sea level.Primary laterite is,whurever pierced,founddto overlie an almost pure pipeclay,and. this in turn a crystalline rock. The laterite is commonly pisolitic,with nodules averaging | inch but attaining a diameter of 1 inch. Alumina is present in all laterites but is most abundant in those over-lying less ferruginous rocks.Iron is present as limonite,but turglte has • been determined. 'Xitania is ubiquitous,probably occurring as mstatitanic acid(S?i02.xH20) although in some places rutlie and ilmsnite are found. Silica is represented by free quartz,although son® of it is likely com-bined in the form of halloysite. Very small percentages of manganese oxide are present,but chromium oxide •was detected in every case,both as chromic hydrate and chromite. Vanadium was also determined in every case it *as looked for,although its form was unknown. Woolnough* offers a very interesting paper on the laterites of the Darling plateau and the Blackwood regionsin which.he makes the following points: (1)Laterite in Western Australia is fornad by the leaching of subsoil slats and the deposition,by capillary attraction,of the formation (2)Laterite can occur only in areas where drainage is almost at a stand-still.. . • • • (3)High-level lateri&fj is a criterion of elevation of the land. (4)Differences in laterite level suggests faulting. Jjeo.l.aag. .,1915. n.365 — soolnough 100 iiatsrite is not confined to the western part of Australia,deposits of bauxite being reported from tile Sorthern Territory,Queensland and Kev? South, scales (see sap 2} The following analyse s"repro sent the passage from a lateritic iron ore (1) , (5) ,and (6),through a typical laterite (2) to aluminous laterites (4) and .(«)'* 1 ' ... 2 • • .3' ' SiGgifree) 0.7&% 4 SiOp TiOg iU20.3 F e2°3 GaO MgO ilnO V2°S Grs03 St " 1.17% 6.06% 4.32% 80.02% trace trace 0.55 % 0,08% 7.06% l.Coolgardie 2 eMfc. Baiter S.Smith's Mill 13.74% 17.17$ 5.96% 2.6755 4.33% 0.59% 2.10% 2.01% 31.14% 46.70fi 44.66$ 9.92% 35.54JS 10.02% 19.08^ 78.32% 0.16% trace trace trace trace trace 0.35% - 0.07% trace trace trace trace • — — - 0.40% — — — — 0.01$ 15.40% 25.37% 27.02% 6.00J& 4.'.Vongan Hill 6 2.75% 5.00% 12.76^ 62.67% 0.99% trace 0.15% 0.08 % . 1 4 . 4 6 % 5.£algoorlie S. « * Bauxite - grosity.Loekisood and Sons.1927 .p.145 -~Foa Bumoold"'gives the following analysis of a bauxite form the locality of Smith's mils JL1203 - 50.68$? , Fe203 - 7.14J& , Si0 2 - 16.05^ tTiOg - 0.62^ and •water 25.95%. * 3auxite and'. Aluminium ~ Imp. last .Ball. .1925 - 3umbold .t>. 73 Mtgrlte^in,Brifcish Guiana''- (see map 3) I_Seol.Mag..1910.p.439 — Harrison In general these earths contain but little combined silica and a relativ-ely high percentage of alusaina.-Ihe presence of free alumina in quantity in the m p 3 100 residual earths characterises rocks where the felspars are minly plagio-clase,whilst residual deposits frosn rocks in which alkali felspars pred-ominate consist largely of kaolinite or of sericitlc micas v.lth kaolinite. In the dense forests of the Guianas there is ansperpetual wet season.The only factor governing the formation of laterite as opposed to pipe clays is the original composition of the rock. The diabase-gabbro type of rock weathers to a gravelly,bright red earth in which is embedded masses of concretionary ironstonetlarge angular ossses of quarts,and numerous small pisolitic granules of ironstone.This material does not possess the property of induration on exposure.In another type the quartz instead of settling out as a&sses and only occurring to a limited extent as fine 3and,occurs as a finely divided sand,the greater proport-ion being secondary.This latter type also fails to harden on exposure,alth-ough containing aluminium hydroxide. The residual earths from sericite and chlorite schists contain sericite, kaolinite,and bauxite with a little residual felspar,often sons secondary veins of quartz being present.These deposits possess the property of hard-ening which is always accompanied by a darkening in color. The result of the decomposition of felsite and porphyrite is a cream-colored .reddish grey,or highly aluminous red laterite.Thin sections show the structure of a aBtamorphosed porphyrite in which the original minerals have been impregnated or replaced by hydrates of alumina in an amorphous concretionary fortn.Little veinlets of chalcedony traverse the material. Ilrosnite Is present as disseminated grains through the slide. She decomp3sition of granite results in a saterial comprising varying proportions of quarts and clay substances,with smaller amounts of col-100 loldal slliGa,ilt53nitatGJQd a very little 1 i n c i t e . Hocks occur which have the appoarance of a tree laterite,is.sottied crean^v white and dark red and having th& property of induration.The composition .however,proves to consist of fine felspathlc rock powder,for the most part, with varying proportions of kaolinit*.bauxite,and oxide of iron. In general ahore a thick mantle of weathered material covers the under-lying rocks the change from ono to the other i's gradationaljwhere the orig-inal rocks are sassive and the covering is thin the transition is abrupt. SCJEB tras bauxites are found .resultant upon the weathering of tho mora basic rocks. k number of interesting analyses are given in Harrison's paper,which ill-ustrate all the types of weathering mentioned above. (see map Si ^ffeese deposits lio at an average elevation of 1900 to 2900 feet above sea level.$he climate is hot and damp,although W % of the rainfall <5c<Mir3 between October and JLprii* She area is underlain by dark colored diabases'composed of lins -soda felspar and pyroxene,with a very little apatite,som magnetite,ami more abundant titanite. • — Wt&Xm •fhe fresh rock lies at an average depth of S5-5& feet be loir the surface. \-here it outcrops*pits of microscopic size .produced by the organic acids of lichens are'C0as»n,plagiGCl3a<4 ia milky and tho pyroseno is rusty In color.In the dry seasozj fissures are filled with grey-brow carbonate ana a conspicuous residua of silica. f .,",•••• ' ' 96 During the weathering of this rock,Ca is removed raore readily than % s S i 0 2 is transported, early,and Ka goes more easily than Ca,products free from Ea often containing considerable quantities of Ga. Most of the secondary material is a mixture of hydrate and kaolinite Y/here an abundant supply of ground water is pre sent, the composition of the final products of disintegration of these diabasic rocks is aluminium hyd-rate; where water supply is moderate and contains humus in suspension the rock goes over to kaolinitic substances. Some analyses of this material are reproduced below; A1 20 3 40-58$ 11% ?e203 5-11% 1S% Si0 2 4-15% -65% SiOg 0.1-2,3% GaO & MgQ 0.11 - 0 .48& 0 .6^ KgO and SagO traces 4 .5^ 29 - 33% 8,0% Later!tic .Deposits of Mozambique* Geol .lias:*. 1914.-p.529 - Arthur Holmas The deposits may -"be classified after Termor as laterite,quartzose lat-erite,and latoritic sand and earth.The quartsose laterite forms hard slag lilte masses .brown on exposure but paler where freshly encountered,frequent-ly cavernous and concretionary,ths holes being filled with powdery ferrug-inous oartheand quarts. •Ihe deposits overlie hornblende gneiss,biotite gneiss,and basalt,the ferruginous varieties being associated with the last. The upward succession is from fresh gneis3 through moist disintegrated gseiss to similar material deeply stained.On this lie the lateritic earths damp in the lower levels but dry above and -pith a strong concentration of 100 components near the surface. The lateritic deposits are irregular in thickness,varying from a fev; inches to a few feet. It was noted that where the forest and undergrowth we re thick,not laterite hut kaolin resulted from the weathering of granite.Sauiiite,on the other hand,see mad to occur where the superficial debris was cleared away ,and the surface was free from organic matter. Lateritic Deposits of India ( see map 4) Lateritic deposits occur very extensively throughout India and per-haps nowhere have they been studied so carefully as in this country.In nearly every case it has been found that the laterite represents the resid-ual product of the prolonged atmospheric weathering of the flat-lying bas-altic lavas of the Deccan.There are examples where the covering laterite has been derived from the weathering of granite.gneiss,etc.but those are rare. In describing the deposits of India fthe following comprehensive description is quoted directly from"Bauxite° by Fox*. * Bauxite - Crosby.Lockwood and Sons,1927.-p.£6 —Fox "It has becoBE increasingly clear in India during recent investigat-ions that there is no genuine case in which primary laterite has formed below persanent ground-water level,and still less so in a lake." "Laterite is not found in the process of formation In the Himalayas and not above 5000 feet In the peninsula.This last is a peculiar fact. Laterite occurs well developed on Malcolm geth (4710jeet>,the plateau above Mahableahwar,but there is no laterite on Kalsubai peak (5396 feet) 100 a little further to the north.Both, hills situated on .the western Ghats, are composed of basalt,and appear to be equally exposed to the south-west monsoon of Western India,Similarly Girliguma hill(S757 feet) is capped with laterite,while Mahendragiri(4919 feet),some few miles to the east of It,has no laterite on its gneissic summit.The reason is probably due to the fact that plateaux of this altitude seldom occur,and laterite cannot form on steep hillsides which slope up to peaks." "It has been found? that, bauxite only occurs in association with the oldest laterites,either as irregular lenticular masses in the primary laterite auntie itself,or was accumulations of boulders on tag slopes or in the valleys below scarps of primary laterite.The detrital acctuanlS-L. 'ations of bauxite are seldom found more than a few miles from their source of origin.and sometimes these agglomerated deposits may be richer than the lateritic scarps from which they have been derived.In such cases a natural separation has taken place;the softer,ferruginous matter has dehydrated, broken up and washed away,leaving the tougher boulders of rich aluminous material behind," cliff of primary laterite Is often found to be. far from uniform in texture and compositional uniform texture and stnucture in a mantle of laterite indicates newly formed rsate.rial.5he typical structure of an old lateritic capping is shown in the accompanying section (fig .c).The variation in. composition and appearance is remarkable,Tho al nost pure pisolitic l ign-ite .yellow and rod when fractured,covers.almost sharply,a bluish-grey or pink to cream colored bauxite.The pisolitic nantie is seldom more than a few inches thick,although at times it is as much as 2 to 4 feet,It has been ref-erred to by Lacroix as the cuirasse de fer.-The underlying contrastingly col-100 ore! bau:ii te ffiay pisolitic,"where exposed,"but usually shows a, veriaicular t e x t u r e f u r t h e r in t h e mass o f t h e mantle . Inwards and downwards t h e e n r i c h e d a l u m i n o u s zone p a s s e s gradually i n t o t y p i c a l laterite•soft a n d v e r m i c u l a r with, v & r i e g & t e d colors »red and yellow and b r a w n and eream«At the b a s e t h e r e occurs the p e c u l i a r 9 c o i 3 p l i e a t e d , l a a i s a t e d i i t h o m a r g e c o m p o s e d of whit© kao-lin,with t h i n s h e e t s of ferruginous c l a y e y matter F i g u r e c . f , f h e r e i s anotherepeculiarity a t t a c h e d to t h e location, o f b a u x i t e m a s s e s in t h e l a t e - r i t e s o f p e n i n s u l a r X n d i a . I n my e x p e r i e n c e enrichments o f b a u s i t -e s ooeor.. .whieii w h e n c a r e f u l l y cons id© red, prove to be s i t u a t e d u n d e r t h o s e c h a n n e l s o f th© s u r f a c e d r a i n a g e l i n e s o f a n d o l d e r p l a t e a u , w h i c h e v i d e n t l y e x i s t e d I n t h e e a r l i e r d a y s o f lateritisation." • The t a b l e b e l o w g i v e s t h e composition of v a r i o u s s e c t i o n s in figure e . A B 0 D £ F § E 1 Si02 3 . 2 $ 2 .4^ 64,. 8% 41 .9$ 37.3% 47.4JS 47 .3$ 10.4 58*4 46 .6 22.0 23.5 27.8 16.7 14.3 f i o / 2.» 4 8 , 9 2 . 5 1.8 ? 7.8 1.7 1.9 70.0 5 .5 23.7 2 .8 10. b 17.3 4.10 4.9 FeO « — — - _ — 10.8 13.5 OaQ — 1.4 10.6 9.4 MgO 0 .4 1 .2 1.1 1..8 0.8 6.5 7.7 fl20 14.0 51.5 30.1 24.5 5.1 14.7 13.4 2.2 1.3 100 0o far the discussion has included only those deposits occurring in tropical climates.Many other lateritic and bauzitic deposits are found in temporaterregions as well.It is generally conceded,however,that these deposits were formed during the tropical Tertiary period.To round out the picture several of the more interesting of these will be described. Laterite and Bauxite in C-ermanv* (see map 5) '* Seoi7lIaa..l908m["-p.Sg4 ~gilroe ' " " ' ' " Kilroe studied laterite and 3ausite in the vro gels berg area of central Germany and arrived at the following conclusions: (1) The laterite,with iron ore,is developed in irregular tracts on each side of a post basalt dislocation. (2)The best iron ore accumulated below a thick more or less ferruginous layer of completely weathered . basalt« (3) This ore was forraad chiefly from lavas of the lowest stage.while bauxite was derived rshinly from succeeding stages. (4) Date of origin likely late Pliocene (Fox suggests Miocene for these) Laterites have accumulated to great depths and to irregular distances up to 2500 metres from ths fault line.The peculiar alteration of basalt has proceeded from boundary lines of composite masses,towards the centre of each 5Eass,in SOES cases leaving cores of undecoaposed basalt .The yellow and red clay resulting from the alteration of basalt Is strongly aluminous and in places contains lumps of bauxite with basalt structure. The following analysis represents a typical bauxite from this regions as n 46 m0% 24.0^ 26.0?; r M P 5 100 The Bauxite Deyosits of Arkansas* (see map 6} iScoa.Geology* .Vol«X<>'5oa.Jaa»191&«p.3& -ilead Two classes are found here,(l) in place and (2) transported.Bis deposits are bounded by wedging out against a rise in the underlying syenite or by an eroslonal valley,are comparatively uniform in thiciaiess9and contain many .clay "horses*'* The prevailing color is light buff.but varies.although not directiy in proportion "co the iron content.A light grey variety contains contains considerable siderite.The hardest portions are uppermost.overlying softer material below .As a whole the pioroaity is high.A great variety of textures appears,the most common being oolitic.comprising spherical pisolites of bauxite in a bauxitic groundxeass.A "sponge" or granitic texture is common ,tlie original form of the syenite being pre served. This latter type usually grades up into the former.and down into kaolinized syenite, then syenite.An amorphous type is also present. The ,chemical content comprises alumina,combined water,silica.ferric oxide, ferrous ozide,oarboa dioxide.and titania.There is a gradation from gibbsite to kaolin. The most important mineral constituent is hydrous aluminium oxide ,in two formsjgibbsite and anx>rphous bauxite.The granitic type is largely the crystalline form of trie aluminium tri-hydrate,while the pisolitic type is predominantly aaorpJious w i t h m i n o r Q u a n t i t i e s o f crystalline m a t e r i a l . Hydrous aluminium silicates are present as we11.in lesser quantity.the most important being kaoUnite,then aalloysite.Liiaonite ana other hydrous oxides •are. found as well.1 • SAP 6 100 i. g r o a t s a E g o t h e r s p e c i f i c occurrences mi g a t te described, but i t i s f e l t timt © c o u g h material h a s b e e n p r e s e n t e d t© gi~e & general picture. h l i s t o f references to othor l a t e r i U - a n d b a u x i t e o c c u r r e n c e s i s g i v e n a t the end of t h i s chapter f o r the information o f a n y o n e w i s h i n g to pursue t h o s u b j e c t fur tier.3a fore g o i a g into the subject ox origin o f these d e p -o s i t s i t s i g h t be o f i n t e r e s t to give a f e w f a c t s a b o u t a l u m i n i u m i t s e l f i s r e f e r e n c e to i t s r e c o v e r y f r o m b a u x i t e * ,3au:ilt& and Aluminium S a u K l t e i s t h e o r e f r o m w h i c h t h e mstai aluminium i s sxtracted.In o r d e r to fca of commercial g r a d e t h e bauxite m u s t c o n t a i n a t l e a s t alumina and n o t over 2 0 ; ? impurities e x c l u d i n g t h e combined wator c o ntent. ®ho g r e a t e r portion {over 8 0 > ) o f t h e world's production o f bauxite i s eonsaaed i s t h e aluadnioa iadastry.Eae o t h e r u s e s o f b a u x i t e a r e s t h e a a n u f a c t a r i - o f a b r a s i v e s (carborundum) .building s a s t s r l & i *h»re nothing b e t t e r i s available,the mmteatar© o f $«ick-se t « n g banalte ceisenta.the asmaf&otare of re free-tor ies,and toe pari f ice. lion of petroleam asa sugar. In the nanufaclure o f tluosiiit the- f i r s t s t e p is the fcreatmsct o f the alumina the B a y e r p r o c e s s from v.hich Is o b t a i n e d pure aicml iiium anhydride.Other p r o c e s s e s e r e snows but a r e relatively aniapomjafc.Sie p r o d u c t f r o m this process I s t h e n refined in sob© f o r ® of an electric far ne.ee, pure alaain-3 tmlns; the result. »0 re-cent f i b r e s are available but tiz 1324 the w o r l d ' s prodoction o f alamiaiaa w a s 156,030 t o n s , c f w h i c h 3 . S . & . p r o d u c e d h h t 0 0 0 t o s s , Central jSoropa 35,000 to»s,Eorway 22,000tons,France 16,&30$ons.Canada 16,000 tons,United -Cingdoa 7000 toasted Italy 2000 tons. to t h e production o f B a u x i t e France and tee U . S . t i . a r e tho sajor 100 producers,v/ith. in 1J24 about 350,000 tons each,British Guiana next with 185,000 tons 9then Italy ulth 138,000 tons .Dutch Guiana follow 65,000 tons with India last v/ith 23.000 tons among the ma^or producers. Ba-uxite occurs in a great many parts of the v;orld,and tae potential world resources are enormous,aa may be gathered by a inspection of the accompanying maps.The British Jimpire is especially fortunate in this res-pect controlling the majority of the.at present, undeveloped deposits. :••.'•. " • 106. Origin of Later!tas and BamtitoB There are few petroSraphical problems which hhve proved so difficult of solution as the mode of formation of laterals.The literature on the subject of laterite is very extensive,and there has been little agreerant as to the manner in *hich it is formed.It would be profitless to attempt to discuss all the different theories advanced,in detail.For the sake of those -wishing to investigate the subject further,however,the- briefest of reviews has been included. Lacustrine Origin Suggested by Mallett? .for the Bauxite deposits of Ulster The residual nature of the Ulster bauxite was later shows by Cole* l a t e r i t e and Bau^Jbg_2one_gjL^.«i!»Ireland ~ Spencer* regarded the bauxite of Alabama as a lagoon deposit Ime^a^qi.c .grouS^^^^ygia J393 .v7zi4 ; ' Bettger* favors the production of these deposits by the processes of weathering,the original material being a detrital clay. Both Vie there 11* and Burton**attribute the laterites of Mysore and the Central Provinces of India to lacustrine deposition. He auMysore aeol.Bopt..vol.i U,pt.1 .1303.pp.1-27 ** Survey India,vol.xlviii,pt.4,1317,pp.204 Fermor*also includes the sub-heading "lafce-laterites" in his excel-lent classification of lateritic deposits. Ijjhat is Later!tn- iteol.3jajTTl911 .n.454. ~ 100 Generally speaking,however.nearly all of the deposits at one tine attributed to lacustrine deposition,have since proved to be due to the processes of weathering under a certain set of conditions.and it is very unlikely that any bauxite or laterite can be satisfactorily attributed to lacustrine deposition. ..Action of Atmospheric and Organic Acids Y.althier*laid gVeat stress on trie introduction of nitric acid dur-ing thunderstorms with tropical rain,the acid resulting in the formation of ; ; - - • laterite* Jferhgndl. de s se 11 .ErdKunde .vol.xvi a186v .v.'618 . . . . . . discusses . . . . . . i^assarge/ a similar origin as ".'althier.and aids other factors,such as Iron -containing minerals.abundance of covering vegetation,and the activ-ity of organisms. —Report of the.6th International Geographical Congress.London.1895 Slciiee * favored the mode of formation of the Upper Zaississippi /alley as being, due to the solvent action of vegetable acids on ferruginous soil. ^eol . jWTlisoroTilQ " ~ ""* ' Liuff* in writing of the laterites of ^ast Africa,considers the most Important factor in their formation to be the action of huaic acids. IjeeiC... in "Laterite and Bauxite In Seraany, -Heql.&tegu,1906 <,p.534 -Kilroe , JIlc.ro -Or Rani s ms The idea of bacteria operating in the formation of laterite was elab-orated in a very interesting paper by Holland*. .Jghe .Ponstitutlon.Origin and Dehydration of uaterite-Greol• Mag.1305.-pp.56-69. This theory is refuted in papers by Mead* .Holases**,and Fox***, ihe Bauxite Deposits of Arkansas - Scon.(teol.1916,VolX.Kol.Jan.p.35 100 ** Lateri tie SopoMts of So sambi q o 1 .Sag . , 1914, p. 629 *** - 0roa&¥.&oc&g&o4 aafl Sons. 1327. t>. 74 -S a L ^ M i i m fross 1&83 to 1^03 ta© bauxites of i .r«caosas ,GeorgiaAlabama were thought*to be due to aolfataric action. Haves Cole* suggested a siailar origin for the bauxites of Eorth-Sast Ireland. _»Trans.Bo?.Dublin See, .volgj.lS96.p.l05 Mebrieh* attributes the- bauxites of the Vagelsberg,Seraany to the actioh of sulfate bearing springs. SLilros* takes exception t o teii presence of sulfuric a c i d a s a n .agent o f attack l a / t h e formation o f t h e s e Yegelsberg deposits,but e x p l a i n s t h e i r formation a s being attributable t e tho action of carbonate-bearing • SsBois* considered that sal far lo acid mast be the essential factor in the formation of laterites. ' ^be above theories have been generally discarded as explanations for the origin of laterite and iJauxite. latere In an excellent paper %wh.ich merits rsore detailed tre£tment,M&claron* I J M J M g l n of Certain lateri t-gs - Sgolu&ftg. .1906.,»..&5g p o i n t s oat t k a t a satisfactory theory of l - a f c a r U l s origin m a t account for: 100 restriction of deposition of lalc-rlfcsa .both g&cgrupuieaily and in altitude (£) Its general superficial occurrence. (5) its interned structure ~porcius »vesIcuiar,piso i i tla , or concretionary. (4| its peculiar composition regards: Inessential alaalcous,ierruginous »or z&mgaul tsravus hydration or oz-ides*. (t»l general presence of ffi&g (c) -JoneraL &bs cr.ce of kaolin or si lice S e c i s r m postulates t h e mz&io&iiy o f altersafcs p e r i o d s o f deasioatioa e n d safearatioa»&s -sell a s t h e g r s s t c e e o f abmsdaat e & r b o n i e estd.£n a mr-lod o f aesslo&tion ovors&fc-uretsd soiatloas a p p r o a c h t h e aurfaoe a&d t h e separation o f s o l i d s oecare..3'ari.ng t h e f o l l o w i n g set s e a s o n t h e s o l u b l e materials p r e v i o u s l y deposited will ao miss^eS,i'm sarl'aea erast i n c r e a s i n g i n p a r i t y & & A h a r d n e s s w i t h -saoh s u c c e s s i v e -set s e a s o n . H e p a i n t s o a t t a & t ; I s tc-rito s a s t b e r e g a r d e d a replaceaisr^t o f d e c o m p o s e d p r e d i c t s o f a - r o c k a M not a direct decomposition product. O n l y on level or approxlastoly lovei s u r f a c e s l a i c rite f o r s . f a i s fcorisentality of sasuf 4eposits»as s e l l a s p i c o l i t i c stractorsa,h&a giirec r i s e to the- lacustrine theory o f 4i»clare» points o u t p i s -olifcio s t r a o t a e e s a r e ml u s u a l l y c a t r a c t o r i o t l e o f opes water c o n d i t i o n s b a t o f l o o s e l y coherent astorlai. ••• -a amlv&em' ' (l)liafcerifcs is restricted gsogritpUiculIy because it requires for its foraatlQB:; , (a) tropical hott and rain vita concoaltact abundant voffotiitloE.totset-100 her with (b| alternating ret and dry seasons. (2} fte restriction of laterite deposits la only apparent, ffiaeir pres-ent lines of alfcitads sorely sarlc anclent or existing valley floors or plains. f 3) they are durived froa mineralised solutions brought to the surface by capillarity and are essentially replacements,of soil or took, decossposad in s i t u . . • . , . . 14} In the has&d regions of India the tendency of change in 1 ateri tes is towards hydration and not dehydration. Cafapbell*,after extensive study of the Istcrites of ?Jest Africa arrive! at a quite similar conclusion sa to their origin as that of Slaclaren in regard to the Indian deposits. .Se says s "IiSterite is a. porous rock:, formed above lcw-w&ter level in the strata on lovr-lying: slopes by t'm gradual removal of sooe,or saosfc of the Mner-al constituents of either alluvium or rock: is sita.and of tha deposition therein of ferric m a aluminous hydrates froa sdneralized water ooaiing from below,the deposition bolng determines Ita contact istth atraosphoric a ir . " Siapson*" although agreeing in genefcal with the sode of origin suggested by the last two £©&*ioas not consider the process oug of replacement,and ref-uses to claes laterite m a residual.instead he considers it a true efflores-cent capping. l ^ k J M m i U . . . l a . . , g e s t g r f t A m t r a l i a , . r . f e o l ^ . M ^ l l i L S i M _ _ According to h is t'as aceussalaticm is slow and cannot t&sre place tsharo . erosion is active .She first step Is the conversion of felspars to teolln and a partial saturation of the sab-surface waters with carbonates of Hss»mg--. a if f • 100 ne 8ia»mansanese.alkalis.with hydrous silica,titania.aad aluaina.Sithe dry weathsr the solution tends to evaporate at the surface and further supplies are brought up bu capillar!ty.Contact with air is sufficient to precipitate all the iron and manganese as hydrated peroxides,evaporation precipitates the others,Alumina and silica in the proportion of 1 Al 2o 5 to 2 Si02 are precipitated as halloyslte but since anaexcess of silica is seldom available A l g e s i a is usually precipitated in the colloidal estate. Titanium is deposited as netatitanic acid. The evaporating water would likewise deposit alkali salta,carbonates and sulfates,which would continue through the dry season,the typical later-itic compounds becoming nearly insoluble through dessication and hardening, with the advent of the wet season ,however, the soluble alkalis,line,and magnesia salts would be removed. Woolnough* agrees with Simpson .but adds some very interesting obser-vations on the physiographic significance of laterites. i . Dec. 1926T^8fi7 He points out that when erosion of an uplifted land surface commences .the earlier stages are extremely rapid,abrasion and transportation are domin-ant and chemical action subordinate. However .when pane plasmatics, is forced to its extreme limit,chemical action completely dominates over mechanical processes of erosion.In sv?eh conditions the subsoil becoiass completely saturated.The con-tact between rock minerals and meteoric solutions is long maintained and rock weathering is profound.In a pluvial climate saturation is complete and per-manent, thus inhibiting effective weathering below a certain depth.Slow as it. i is there rsrast be a seepage of ground water towards drainage bottom.Given suf-ficient tins thh soil and sub-soil must be leached completely of all soluble 112 • m a t c r . l a l s . - i l l a l k a l i s ,&l*almo e a r t h s , a n d Magnesia a r e r e m o v e d a n d s o m e i r o n a n d alutaihinn a s w e l l , a p o r t i o n a s s o l u b l e s a l t s b u t m o s t l y bin t h e c o l l o i d a l forruSoro c f t h e s i l i c a i , d i s s o l v e d i n the a l k a l i n e solation.the r e s t g o i n g i n t o c o l l o i d a l f u s p ^ n c i c n . D u r i n g t h e wet s e a s o n .however,in r e g i o n s o f seasonal rainfall.the r e s u l t s a r e soaawfiat differenttftater.^fcng. a b s o r b e d greedily c a r r y i n g atmospheric g a s e s to g r e a t depths.iJaring c o n t a c t , l o n g o r s h o r t w i t h the r o c k mineral8,tho w a t e r s c a r r y o n d e c o m p o s i t i o n and the e f f e c t s a r e c u m u l -a t i v e . D a r i n g t h e p e r i o d o f dessicatioc oapixiarity s u p p l i e s moisture f r o m the d e e p e r lecels o f t h e s o i l an* s u b - s o i l . . b a r g e a m o u n t s o f d i s s o l v e d m a t -e r i a l a r e b r o u g h t to the s u r f a c e a&d d e p o s i t e d a s a n efflorescence.which d u r i n g s u c c e e d i n g w e t spells i s moved i n t h e d i r e c t i o n o f drainage.Under normal c o n d i t i o n s .howver.the niost s o l u b l e f r a c t i o n i s r e m o v e d a n d c a r r i e d s e a w a r d s as i n a pluvial climate.The l e s s s o l u b l e components a n d t h o s e o f a c o l l o i d a l c h a r a c t e r behave d i f f e r e n t l y f o r d i f f e r e n t climates.Prcduced i n t h e s u k - s o i l u n d e r c o n d i t i o n s o f c o m p l e t e s a t u r a t i o n a n d o f d e f i n i t e pH concentration,the constituents e n c o u n t e r d i f f e r e n t c o n d i t i o n s a s t h e y migrate u p w a r d s . U s u a l l y l o n g b e f o r e t h e y r e a c h t h e sjurface.the c o l l o i d s a r e p r e c i p i t a t e d , g e n e r a l l y a b o u t a nuiaber c f i s o l a t e d aucleii i n t h e s o i l , M r ~ lnS 'tize.ensuing -.poridd o f s a t u r a t i o n t h e descending solutions approximate more c l o s e l y i n p H v a l u e t o t h o s e p r o d u c i n g p r e c i p i t a t i o n than t h o s e f a v -o r i n g s o l u t i o n . A l t h o u g h t h e r e i s l i v e l y to be some r e - s o l u t i o n , i t w i l l be s u b o r d i n a t e i n a m o u n t . I n t h i s w a y a n amorphous d e p o s i t a c c u m u l a t e s i n t h e s u b - s o i l . u s u a l l y o f a n o d u l a r o r c o n c r e t i o n a r y n a t u r e . A c c o r d i n g - t o t h s s t h e o r y l a t e r i t e c a n o c c u r o n l y i n a r e a s w h e r e d r a i n a g e is a l m o s t a t a s t a n d s t i l l . H i g h - l e v e l l a t e r i t e i s t h e r e f o r e a c r i t e r i o n o f i 1 V 113 elevation of the land ,and difference of level between latsritos suggests faulting. Fox* summarises' the subject of the formation of laterites as follows; Bauxite -Crosby.Loekrood and Sons.1927 - p.SQ-OS rtI have been led to the conclusion that the conditions necessary for laterite formation be expressed as follows: (1) A tropical climate subject to alternations of wet and dry seasons or monsoons . •••••...••... (2)A level,or very gently sloping,elevated land surface which Is not sub-ject to appreciable mechanical erosion. o (She -chemical and mineralogical composition of the exposed, roe.es to be suitable for a supply of lateritic constituents-alumina and ferric oxide. (4} She texture of the rock to be (or to rapidly beeone) sufficiently por-ous for the entry of percolating water,so that the conditions for chemical action will be at a rasxiaam. (5) The infiltrating water to re stain in the interstices of the rock: for long periods annually,but eventually to drain away in the dry period,thus giving maximum play to chemical erosion. (6j'rhe infiltrating water to contain either an acid or an alicalice substance •p/ith which to react on the rock components,as well as to constitute an electrolyte and allow elsetrofcinetic phenomana to operate. (7) These annual processes to be in operation continuously for at least a geological epoch of roughly a million years (counting the ;SLocene epoch as of this length and the Cretaceous as five timos this amount.;." "With the- development of colloid chemistry and the discovery of the . colloid nattee of most clays,a new light was thrown on the origin and i, ill-100 c o n s t i t u t i o n o f clay*.info n a t i o n i s a v a i l a b l e t o s h o , t h a t many c l a y s contain a l u m i n a in a soluble f o n n m C evidently n o t in c o m b i n a t i o n with oilica.bfclng present in hydrated form as a gel . It is no* thoa^t by aany chemists that rock- s i i i c a W s a r e subject to prolonged atr*>spheric weathering,they brea* dow, d i r e c t l y i n t o c o l l o i d a l hydroxides(hydrosoIs J , a n d n o t i n t o h y d r o u s s i l i c a t e s a s a f i r s t s t a g e . A l s o t h e s e s u b a t a n e e s , the c o l l o i d h y d r o x i d e s d e v e l o p e l e c t r i c c h a r g e s . , s o ® positive (usually t h e b a s e s l i f e f e r r i c o,:ide a n d a l u m i n a ) .other, negative ( l i t e the S i l : r o s o l } ,\Tith r e s p e c t t o e t c h o t h e r s * the e l e c t r o l y t e ( a i r l i n e o .er .tea. hyd-.'Or . ac id 'wat er which. is s f f e e f c i n g tho d e c o r s i i i o n j i n which they are contained.Furtfc these oppositely chared :aydro,olssif n o t i n a n y v:ay p r o t e c t s o r separated d u a l l y - p r e c i p i t a t e e a c h o t h e r , n o t a s a m o r p h o u s a l u o i n o - s i l l c a t e s . b u t a s a -aiixture o f s i n g l e gels .* "In r e c e n t y e a r s a n o t h e r a s p e c t ' o f the case,in p a r t i c u l a r r e d i n g a porous d e c o m p o s e d r o c k mantle,hfe3 developed. - • 1 1 ) S h e n a n e l e c t r i c a l potential i s a p p l i e d t o t h e o p p o s i t e s i d e s o f a porous diaphragm,immersed i n a n electrolyte,tae liquid i s f o r c e d t n r o u - h ths d i a p h r a g m w i t h the c u r r e n t . ' I b i s p h e n o m e n o n i s c a l l e d e l e c t r i c a l e n d -.0BSJ0S8V U ) I f t h 0 s o i w .instead o f being- is the form o f a porous diaphrasa,exists l n a S t & t e o f suspension's In a c l a y ' s l ip ' , the s o l i d raigratc-a t h r o u g h the l i q u i d to one o r o t h s r p o l o o f arj . e l e c t r i c current w h i c h my be p a s s e d t h r o u g h . S h i s paeno-cnanon I s a s cataphoresis. ( 3 ) I f a s I n ( I j the -solid i s f U e d i n the f o r m o f a p o r o u s d i a p h r a g m , a n d liquid i s f o r c e d through its p o r e s i n o n e d i r e c t i o n , ^ * a d i f f e r e n c e o f e l e c t r i c p o t e n t i a l i s developed between tae i n a n d o a t extremes o f the 115 • diaphragm.aad a n e l e c t r i c current m a y «e e s t a b l i s h e d b y c o n n e c t i n g t h e s e p o i n t s , • 4 } If the solid,in f i n e l y d i v i d e d s t a t e . i s d r o p p e d t h r o u g h t h e l i q u i d a d i f f e r e n c e o f e l e c t r i c a l p o t e n t i a l i s established.between t h e u p p e r a n d slower liquid atrata*!t . " T h e a b o v e rasntioned phenomena furnish raach f o o d f o r thought i n connec-tion with the formation of iaterite,particularly with regard to the remov-al o f c o l l o i d a l s i l i c a a n d h y d r o u s silicates,and t h e narked s e p a r a t i o n a n d segregation o f llaonit® from the b a u x i t e . F o r e x a m p l e , i f a laterite m a n t l e be treated a s aporous diaphragm.and the percolating w a t e r { c a r r y i n g n i t r i c o r carbonic a c i d ) b e considersd a s a n electrolyte.it i s evident t h a t eleotroicinetic phenomena mustvoccur.The s t e a d y d o w n w a r d t s o v s s e n t , d u r -i n g the- w e t m o n s o o n period,of too percolating rater.xvith i t s d i s c h a r g e f r o m s p r i n g s a l o n g the base of- tne l a t e r i t e scarp,will not be t h e o n l y i n f l u e n c e a t w o r k t e n d i n g t o s e p a r a t e the s o l u b l e a n d c o l l o i d a l constit-u e n t s . In t h i s c o n n e c t i o n certain peculiarities h a v e b e e n o b s e r v e d w i t h r e g a r d to the i n t e r n a l struetv.ro of a laterite m a n t l e . " T h e d e g r e e o f separation i n t o trie v a r i o u s constituents s h o w n I n t h e a c c o m p a n y i n g s e c t i o n , I s in isany i n s t a n c e s v e r y r e star Stable. The a l m o s t p a r e li l i s o n i t i e c o v e r i n g i s a b r u p t l y 1 u n d e r l a i n b y a r i c h c r e a m - c o l o r e d t o b l u i s h -g r e y bauxite,which i n t u r n passes d o w n w a r d i n t o a s o r e a n d .more t r u e later-itic type.richer i n s i l i c a , e t c . . u n t i l f i n a l l y , a n d r a t h e r abruptly.at the base tne re o c c u r s a p e c u l i a r , i r r e g u l a r l y l a m i n a t e d lithoaarge a s s o c i a t e d w i t h f e r r u g i n o u s l a y e r s . " " T h i s r e a s r i a b l e s e p a r a t i o n o f f e r r i c h y d r o x i d e . a l u m i n a , a n d h y d r o u s s i l -i c a t e s o f i r o n a n d aluainiua arrosts a t t e n t i o n . I t rould s e e m t h a t d u r i n g y i a u U ^ I u a _oy UA'i'aR la LaT^ITa .jikggL* I - il ^ • • ' . j. - , • . ' • • . ' • • ' ' T 1 1 5 .! f • ".. ' • • • ' • . . • • • • ' - . • • . . • . . . si; the rains the leaching action of the rain water,charged, with corrosive acids or salts,as it percolated into and down through the interstices of the rock ?nd then outwards to the springs at the base of the laterite- scarps,most i l l ! carry away all soluble or finely suspended n&terial.The formsr would be carried P away but the latter seeras to .&hve been deposited as lithoa&rge.At the close of • - .v. ••:•,. • ' • : . .jr. the rains,a»d with the cosing of the dry weather period,powerful capillary j il • action would be induced,whoreby the liaanite would be dra-n to the surface from the -/.one j u s t be low* T h e reasovsl o f f e r r u g i n o u s m a t t e r w o u l d t h u s gradually lead to tho formation of a bauxite zone if the silica has also been removed. However,the removal of silica cannot be thus siraply esplainod.lt seems clear • ..-•.-.•••-•••. ... V. - . ' " ' . . . - . . . . . . - : . ; , - •• • . . -therefore that olectro£inetic p h e n o s s n a must operate,ani that the efficiency of the e f f e c t is due to the silicate rsinerals having been brolcen d o w n entirely into component sols a n d g e l S o T h e steady flcv. of water {see a c c o m p a n y i n g figure) down through the porous tsass of :L„-co repose a rock ,and the p r e s e n c e of colloidal e l e c t r i c a l l y - c h a r g e d p a r t i c l e s supply a l l the e l e c t r o k i n e t i c conditions which are necessary,in addition to t h e i e s o v a l by s o l u t i o n a n d in suspension and upward c a p i l l a r i t y a l r e a d y vsDntioned.for a c o m p l e t e s e p a r a t i o n o f t h e v a r i o u s constituents.The aluminium hydrogel3 w i l l r e m a i n p r c a t i e a l l y -stationary a n d fonetlon i n the posaus s o n s a s a n imperiBssafole •aen&raae.The p o s i t i v e l y c h a r g e d •• ferric hydro gels w i l l be actuated u p w a r d b o t h by c a p i l l a r i t y a n a under e l e c t -r i c a l a t t r a c t i o n of t h e e l e c t r i c a l p o t e n t i a l o f t h e upper p a r t of t h e l a t e r - • 1,! lte zone.She negatively c h a r g e d silica,it «el or s o l f o r m , w i l l be influenced downward both b y t h e downward c u r r e n t o f water and u n d e r t h e e l e c t r i c a l draw from th© p o s i t i v e l y c h a r g e d electrical p o t e n t i a l i n t h e l o w e r l ayer ,The neut-hydrous silicate compounds v.lll gravitate in suspension with the relativ- . ely rapid downward flow of the percolating water,and be precipitated .where the } . , • • ... : • •:•• : • • • . . - . . . . . - . • •• . • |<(f | . : • M 117 the velocity Is greatly reduced,ie, at the foasecof the laterite nan tie. The SSdns iiDurandl seems clear by such ar explesetion,but the very nature of the process appears to bo subject to so many difficulties that It would seem almost a hopeless task to try and o b U i n experiosntal evidence is support of such a theory.The several factors,as stated previously,have been verified in operation in other cases,and have been utilized with a vietr to commercial processes}but as to whether these factors can bo proved to be in active oper-ation in laterite formation is still amatter for demonstration.She electrical potentials in the top and bottom of a laterite layer are likely to be som suaII,and the d i s t u r b i n g Inflaences so l a r g e , t h a t it is doubtful I f conclusive proof of the existence'of such a difference ofnpotentld could be established, the greatest factor is U TO .The processes of roc*-dvcay,the annual removal of soluble constituents and the deposition of suspended particles,are exceedingly slow and naintalned for vast, periods of time.She exposed sections of laterite that we viu- shovr the cumulative result of countless repetitions of small effect ,which have steadily operate* in the separation sJd segregation of the chief constituonts-the' aiamiiiiura attd ferric iron hydroxides from each other and from the silica which was o r i g i n a l l y present." £ot what complication- are present as to Changs s in the nat-ure of the electrolyte as it gets down into rocjts of various types.It is well known that the phonos;r,a of basic exchange occur in soma underground waters.It is also well established th&t the composition of the infiltrating water,before anA alter it enters the roclc,can be different in different areas ana depths eg. percolating waters on a bare country will not be contaminated with organic Matter as on a well-wooded region.and it is obvious that the presence of pyrite i n -ocit must affect thy composition of the water belov; ground,and thus mod-118 t h c slTrplicity of electrokirst.!c action as outlined above.And yet tha very ' f a c t t h a t tho i n f i l t r a t i n g w a t e r p e r i o d i c a l l y d r a i n s almost completely a m y ^leaving the I n t e r s t i t i a l s p a c e s o p e n t o the access o f a i r l B & y h e l p to r e d u c e the abnovasl f e a t u r e s and m i c e t h e conditions sonanvhat general f o r t y p e s o f o f l a t e r i t e formation.Abnormal features,such as the composition o f ' the o r i g -i n a l rocfc.v/ill be e v i d e n t i n the composition o f t h e resulting l a t e r i t e e g . © a p r e s e n c e o f P y r i t e , s a y , i n the o r i g i n a l s h a l e v . i l l p o s s i b l y a c c e l e r a t e tho r a t e o f f o r m a t i o n o f good b a u x i t e . b u t l e r v e a p p r e c i a b l e t r a c e s o f s u l f u r in the b a u x i t e ; o n the other h a n d a n a b u n d a n c e o f i n s o l u b l e constituents.such ss « tan ia i n a n o r i g i n a l basalt,will r s m i n i n m a r k e d aoouut. as a n i m p u r i t y t h e resulting bauxite a n d may nesesBltato the n a ^ t i t a n i f e r o u s bauxite,as in tte c a s e o f aany Indian bauxites.1 ' W i t h t h i s s o ^ v / h a l ; l e n g & h v . i f interesting excerpt,the s u b j e c t o f l a t e r i t e m £ b a u x i t e t i l l b e d o s e d . S e f a r s completing the chapter.However,the subject of k a o l i n a n d i t s f o r m a t i o n v-ill b e d e a l t -M th briefly,as M i l t h e c o l o r o f rsa beds .neither o f tbsse r i g h t l y b e l o n g i n t h e c a t e g o r y o f "tropical w e a t h -e r i n g " , b u t i/s lieu o f a more s u i t a b l e p l a c e M i l be t r e a t e d here. 119 1'lie Origin of Kaolin The term kaolin is used for a rock material that is low in iron and usually white in color,composed predominantly of the hydrous aluminium silicates of the "Kaolin" f a m i l y ' s well as .commonly.indefinite amounts of allophane.She term kaolin isuusually applied to the rather indefinite sub-stance resulting from the decomposition of felspars as well. There has beenconsiderable controversy over the mode of formation of kaolin,SORB observers attributing it to hydro thermal action,while most consider it to be resultant upon the decomposition,through weathering,of felspathic rocks. 2he v/ork of Boss and Kerr* ,has served to throw light on this sub-ject,and possibly clear up the various difficulties.Mieyhave noted three kaolin minerals,differing but slightly in optical properties,kaolinite, nacrite,and die-kite* the first undoubtedly results from the decomposition of felspars,while the other two appear to be of hydrothermal origin. Jhg_gap_lin Minerals - U . 5 . S . S . .Prof.Paper 166-iS .1931 Withe this brief staterasBt the subject wi 11 hereby be dismissed, tlie following references being suggested should the reader wish to pursue the question furthers (1) A Descriptive Petrography of Igneous Bocks,-tfniv.of Chicago Press 1932 -p.212,~Johann3en (2)Beitrage zur Sentniss einigsr Xaolinlagerstatten- Eeues.Jahrb.,B.B*Xv 1902,pp.£31-363- Ueinschenk I3)\7eisse Erden Zecke St .Andreas - 24itschr.f.prak.0eol. ,XIII ,1905,p337 ••.. -Stutzer (4}iaolinization and Other Changes in \?est of England Eocks— t Mineralog.iGag. XV,1908,p. 146 —Butler iSjGeol.of Country around Bodmin and St.Austell — item. Sec l.Sur.fing, and Wales ,1909,pp 64-68 - Flett (S)Beitrag.zur Frage der aaolinbildung -Jour.f.Prak.Chemie,LXXVIII,1908 ,pp.260-284 -flahnel l7)Die Pneumatolutische tCao 1 inver.vitterung—Zeitschr.f.Anorg.Chemie LXVI,1910,pp.343-357-- Van 3em®elen . 120 .• • (8)1 Handbook to the Collection of Kaolin,China Clay and China Stone in Museum of Practical Geology.Jermyn St.London-London, 1914-Hov:e (9) Pundaoantal Principles of Petrography -1916,p.77 -Weinschenk and , . . .. •  Johannsen (10)Mining Magazine - 1S87,VII ,p.213-Collins (11) Hote on Formation of Kaolin .Minerals from Felspar-Jour.Qeol. volXL ,Ko8,Eov-Qec,1932 8 (12) D . S . S . B u l l . 1 8 2 , p . 7 3 , 1 9 0 1 — Hansoms {13)tI.S.S.S. ,21stAnn.Rept. ,Pt.2,p.262,1900 —Weed (14) U.S.fi .S. ,17th.Ann.3ept. ,Pt.2,p.436,1896 —.Emmons (15) ^con.Seol. II ,1907,p.690-(Can.Geol.Sur.,Mem. 113,1919 (17) The Origin of Kaolin -icon.Seol.X,1915,pp.89-93 -Lind^ren (18) Mineral Deposits - McGraw-Hill,1920,p,372 -iindgren (19) A Beview of the Theories of the Origin of Uhite Residual Kaolins-Trans .Am. Ceramic Soc.,XIII,1911,pp.51-74—Sies (20) Clays.Occurrence.Properties and Uses- John Wiley and Sons,1927-Hies and etc. In general the bulk of the residual kaolins encountered may be attributed to the action of weathering processes. The,, Color of Bed Beds The origin of the color of red feeds has long been a question of great, Interest to the geologi cal world .A brief mention of sows of the more recent conceptions of thsi subject will be briefly reviewed here. It i s accepted that the red coloration is due to iron.Two Quest-ion's arise howevert (1) Is the red color due to a larger iron content than in the non-red rocks? (2}is the color due to iron in a form different from that, found in non-red rocks? (1) Everything else being equal the worn iron present the more intense will be the coloration.Hqv?evervit is not the quantity of the iron to which the color ma$ be attributed but rather to the degree of oxidation a»d dehydration -to which the iron has been subjected which gives rise to the intensity of coloration. 121 (2) Ferrous oxide in the presence of air is almost immediately oxidized to the ferric for in, the latter being very stable -and almost com-pletely insoluble in water.It is obvious therefore that i f sediments are laid down under oxidising conditions much of the iron will be in the ses-quioxide state.In general red beds have an excess of ferric oxide over ferrous oxide.- • . . . . - . However,anny beds higher in ferric iron than any red beds are not red.Karlier in the chapter,the various so-called hydrous oxides of iron were discussed.The point that is notable is that as the amount of hydration is increased the iron becomes less red.The redness of beds is not dependent .therefore,only on the amount of ferric iron pre sent,but also on the extent of dehydration which has taken place. iixperiiasnt has shown that ferric hydrate will eventually lose water and turn red by itself if given enough time.Hydrated iron sesquioxide is not a stable body and even if kept under water will teafd to become dehydrat-ed,as long as it is not in isoleeular combination with other oxides.Elevation of' temperature and increase of pressure tend to accelerate the actiofc. Another point enters,as emphasised by aecCarthy*.Basing his deductions * I rnn StnSned Sands and Olags-Jour.aeol. upon a series of experinsnts,hs found that quartz becomes iron-stained only in the absence of more active adsorbants -orthoclase stains more readily than quartz as does hydrous aluminium oxide.Pure kaolin ,on the other hand ,is a paor adsorbant,unless activated by some substance such as alkali carbonate. In many beds where kaolin predominates,the amount of ferric iron is a function of the alkali content,which in many residual deposits and clays is dependent on the colloidal content. 122 Soi-sey* considers that desert conditions are not necessary for the formation of red beds,an that moist,warm,forest covered zones are acre suit-able,The primary requisite for ta« acquisition of redness is tins,although heat and pressure are helpful,Active drainage is some aid by removing red-ucing agoats*Be& bode are continental rather than marine insofar that reduc-ing conditions arc- typical od' deposition' on continental shelfs. of Bed jfeds- Jour.Pool. j u m y . f f o . 2 ~ In general color is a function of geological age,It is also a funct-ion of the amount of hydration,as well as tho physical state of the oxide? the latter if present as earthy iteaatite would give rise to a color different thau that consequunt upon ths presence of crystalline hematite. Barrell* points out ta&t alternations of seasons of warmth and dryness with seasons of flood are eontributive to the origin of red beds.This alter-Ration might result in hydration but; does effectively oxidise the ferruginous material present.' JLUaafo, , pos its - Jour, ire ol, . m .Ko.3.190S -n. 28 5-Bar re 11 123 BiftllOCTaphy £he following direct references are made,in the order of their occurrence,during the course of this chapters {1} A Journey from Madras through tte Countries of t5ysore,Canara,and iklabar — London,1807,vol«ii,pp.436-437 -Buchanan (2) ivhat is' Laterite? - Geol.Mag. , 1 91 l , p . 4 54 - Pernor (3) Ann.des Mines , vol . vi,1821,pp,531-534 - Berth'er (4) Jahrbuch.fur Min. ,vol .ii ,1898,pp.192-219 - Bauer (5) Geol.Mag. ,1903,p.59 -Holland (6) Bauxite - Crosby.loctarood and Sons,1927 ,p .3 --Fox (7) Idem -p.36 (8) Idem.-p. 42 (9) Mississippi State Gaol.Survey - Bull .19 ,1923 ,p .1 - 'Morse (10j Geol.i'Jag. ,1903,p .59 - Holland (11} Descriptive Mineralogy - John wiley and. Sons,1926,15.431 - D«n& (12) Shin-Seetion Mineralogy - 5Sc3raw-Hill,1933,p.l76 -Rogers and 113)Bauxite - Crosby.LoeSwood and Sons ,1927 ,T>.49 - Fox (14) Idem -p.60 (15) G-eol. 2ag. ,1903 — Holland (16)f!3ie Hydrous Oxides - ifcaraw-Hill,1926,p. 107 - Weiser (17) Data of Geochemistry - U .S .G .S . , 3ul l . 770 , 1924 ,p . 501 - Clarke (18) Bauxite - Crosby,Locfewood and Sons ,1927 ,p .59 - Fox (19) Idem - p .60 (20) Physico-Ghezaical Geology - Arnold,1927,p.241 — Hastall (21) Bauxite - Crosby ,iockt?ood and Sons.1927,np.61-62 - T?ox (22) Idea - p.65 ' (23) Bull 30,U.S.Bureau of Soils,Dept.of Agriculture,1905 - Caceron and Snow (24) Later!zation in Sierra Leone- Geol.Mag. ,1921 t P . 213 - Mxey (25) Bauxite and Aluminium- lap.Inst .Bull ,1925 ,p .63 - fiumbold (26) Observations on the laterite of West Africa - "Eraus. Inst .Mia. Jfet. vol.xix,1910,pp.432-457-Campbell (27) Hhodesian Laterite - 3eol.Mag,1909,p.350 — Uennell (28) Laterite in Western Australia - Geol.Mag. ,1912,p.399 - Simpson 129) Geol .3ag. ,1915,p .385 - Soolnough (30) Bauxite - Crosby,Lockwood and Sons,1927 tp.l43 - Fox (31) Bauxite and Aluminium - I mp.Inst .Bull . ,1925,p .73 - Bmabold (32) Laterite in British Guiana- deol. ilag.,1910,p.439 - Harrison (33) ferro Soxa in Sao Paula,Brazil- Boon.Seol.May 1934,p.280 - Freise (34) Later!tic Deposits of I&zaiabique - Qeol.Kag. ,1914,p.529- Holies (35j Bauxite - Crosby,Loctoood and Sons ,1927 ,p26 - Fox " (385 Iron Ores of Korth-iSast Ulster - See.Geol.Sur.India,xiv, 1881,pp.159-1 4 8 . - Sallett •syj Laterite and Bauxite Zone of E.ii. Ireland - Geol.Mag. ,1908,p.471-Cole (40.) The Palaeoxoic Sroap - Geol.Sur.3eorgia,1893,p.214- Spencer (41) Bauxite Deposits of S-B Alabama - Ec on. Se o 1 . ,XX ,liov. 1925, p. 674-He t tge r 124 (42) ilea.Mysore Geol.Dept. , lii ,1906,pp.1-27 - \veterell (43) Bee.Geol.Sur.India,xlviii,pt.4,1917,p204 - Burton (44) What is Laterite? -Seol.Sag. ,1911,p.454 - Ferator (4b) Verfaandl.Gesse11.Erdkunde,xvi,1889,p.318 - walthier (46) Beport of the 6th International Geographical Congress,London,1G95 - Passarge (47) Geol.Mag. ,1680,p.310 -McXee (48) Laterite and Bauxite in Gerniany-Geol.Xag. ,1908,p.534 - Kilroe (49) The Constitution,Origin and Dehydration of Lateri te-Geol.iSag. ,1903 pp.56-69 — Holland (50) The Bauxite Deposits of Arkansas - iicon.Geol. ,1915»X,Jan.p.35-&>ad (51)L&terite Deposits of Mozambique- Geol.^ag.,1914,p.£29 -Holaes (52) Bauxite- Crosby,Locicv?ood and Sons,1927,p.74 - Fox (55) 16th Ann. Sept . ,U .S .G .S . ,pt.3,1895,p.547 - Hayes (54) Trans.Roy.Dublin Soc. ,vi ,1896,p.l05 - Cole (55) 2eitschr.f .Kryst. ,xxiii ,1894,p.296 - Liebrich (56) Laterite and Bauxite in Germany - -Geol.Mag.,1908,p.524 - Xilroe (57) Tscherm.Mitth. ,xxii ,1908,pp. 1-61 (58) The Origin of Oertain Laterites - Geol.Mag. ,1906,p.536 - UacLaren (59)The Origin of Laterite -Trans.Inst.MIn«last* »xix,1910,pp.432-457 -Campbell •• • i (60) On Laterite in V/estern Australia- Geol.Mag.,1912,p.395 - Sinrpson (61) The Origin of Vi'hite Glays and Bauxite - Econ.Geol. ,xxlii,Dec^l928 j p. 887—lYoolnoufjh (62) Bauxite - Crosby,Loclcwood and Sons ,1927- p.80-85- Fox (63) The Kaolin Minerals - U.S.G.S. ,Prof.Paper 165-Ii,1931-Boss and Kerr (64) Iron Stained Sands and Clays- Jour.Geol.,xxxiv ,1926 ,p. 352-SSacCarthy (65) The Origin of the Color of Bed Beds -Jour.Geol.,xxxiv,1926-Porsey j (66) Climate and Terrestial Deposits -Jour.Geol.,xvi ,1906,p.286-Barrell j For a general review of the subject of laterite end bauxite the ! j reader is referred to"3auxite",by Cyril Fox,not only for the subject aa&t- ; ter but for the very extensive bibliography attached.Another briefer»but j! excellently written woric on this subject is the Imperial Institute's Bull- i! etin on"Bauxi te and Aluminium " by Bumbo Id. Tho latter gives a very complete h 1 picture of the British Umpire's resources of Bauxite from a regional point |ji. 1 •of view. .••••••• ... I HI II?i I !!' r i ' f i V THS . WBATHSBBD "BOO&S OF HOE'S KOlsd by John Moss Cummincrs • v<V' : A T l i t i S I S Presented in Partial fulfillment of the Requirements for the Degree of . M&STBB OF APPLIED SCIMCli in GEOLOGICAL BEGIMEBIU& 'Volume 'Two April 1935 liSUL mMmLjm& Class!floetlon * . . . "...page 125 Microscopic ixamination . . . . . . . . « XES Chemical JSxaralnatloc « j_20 MmM^MLl. General Inscription • . « ig£ Microscopic Examination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . « £32 Chemical Sx&aimtloa « j,gg Eemaris w 138 General Description n 140 slicroscopin Ixamlmtiott . . . . . . . . . . • » . . . . . . « « , . . . , . » » , . . » » 140 Chemical Examination » 142 Banarte " i>ag • M s i l a J c m Seneral .Description n 146 -iicroscopic examination » 14s Chemical Semination " 1 4 ? .Kesaar&s » iso General Sussary and Conclusions l.Sansnary . . . . « » « • • . . . . . « » . . . . . . . . . . 0 « . . . . . . . . . . . « 152-^.Conclusions » 3.54 FOSR Song fton* Irani te Sample XI Olassifioetion.. « 1 5 7 aUcroSCOpiC t;K:i«i33 tiOC . , . " 158 Chemical anamination . . . « . . « . . . . „ . " 160 Sample K2 £ensral Description . . . . « . . . . „ . , . . . . . . , " 151 Microscopic KxaaiiatioiJ * 1S2 Chemical jSxaaln&tion * 186 X e a a r i c s . . . » " 1 6 8 General Description " 170 Microscopic iixaainafcion • - « * • • • . • • • • « • • » . . . . . . « • • . * • • , . . • • . « 171 Chemical Semination " 174 HeaarJca " 176 3arm>le, M , General Description . . . . . . . . . . . . " 176 aiicrosconic Sxaminatioa . " 177 Chemical Examination " 175* ItOfimrfes . . . . . . . . . . . . . . . . . . . . 176 175* - equals 176 . Sarole f 29 •3enerai So script ion „„„ .pagel?? ilieroscopic Eraraination « » , , » » . . . * » X76 . Chemical isxaoination . « jgi Semrks «»<?*«* . , , , . , . • . . » jjg JsvnlQ.i.Hi h,. General description « jjg Microscopic Jsasination » « » , « . « . ' # ies Ohsraicc:.! iijs2.aii5ation • ** xe? General Description « 3J0 Microscopic ixamination . . . . . . . . . . . . . . . . . . . . . . . . . . « "Cfeeaical Exas&imtion , « • , « , . „ . . , . , . « . , « , „ „ , • « „ . , . „ , » , » , „ „ » ifg General description . . . . . . . . . « J s s i a l ^ ^ f i ^ i ^ J a s s i M l f i a s l.Sieaisarf . » . . . . . « • » . . . « » . » . „ » „ , » , ( , . „ , . , , . » . . . . . , . „ . . , , . . * lit E.Conclusions " 200 MrnsmMm. j'lst© 1 ~ ¥3? (Crossed -56 $ • 'Slate 2 - 75? d#(Cr«»sdd Sicols^X S60] ftlXefi fssetar© in quarts phenocryst « 132-iss Plate 3 - 757 fl, (Grossed 2ieola,ii 80 | n&mrMi-m aono about quarts phenocryst ... «• Plat© 4 - 1 37 0,(Cfo»da8d Slools,X ml Kaolinite crystals a ? M s g altos of original felap&r phoaocrysts *» 140-141 S ?S? 0 ,(Crossed £leols,£ 350} IKtety .Jeaoli&lie and hy&roa&ea « 141-142 5 b«- V37C grossed, Sicols.2 360) Vertalcular Kiolinita crystals » 141-142 *lat* § « f «{<jr03eed Slcolsv2 SSI Soxfcar© » M&-M7 Figure i - Progressive changes in certain &&t ioe«» . „ « « 163-154 Figure £ ~ Relative gains ectl leases of ooEGtiU»Bts.» 165-151 figars 3 - Afcaolttte changes in constituents * i m - l U figar© 4 - Selative laineralogio changes » 155-154 JSasassaMsfis^is, ^xate V l » c P l a i n t > i m a texture H a t e S - £ 2 , {Grossed Eieols,2 M J Gesture and &ia'ferenti«*I weathering Plate t - 2 (Grossed £Icole»Z SS-3 ) Differential alteration of albite and saicrocline . . . . . . . . . . . . . . . . flat® 10 - K g^fSajBsea Xiicols, X 360) Secondary coraplex after felspar . . . . H 158-159 " 161-162 •« 162-163 « 163-164 Plate II , (Grossed ricols,S 80} Secondary Complex.showing staining along original original cleavage lines . . . . . . . . p a g e 163-164 Plate 12 « ( Grossed iiicols,X 560) Partial- replacement of quarts by secondary Kateri al " 164-165 Plate 12, 2 3 , ( Plain Light, Z 34 ) Texture and staining « 170-171 •Plate 14, & 3 , (Crossed Kicols, X 54 ) Sexture " 171-172 Plate 15 , K 3 , ( Crossed Eicols#X34 ) Solution of quarts » 171-172 Plate 16,X 3 , ( Crossed ttlccls, X 360) Xaolinite and hydrozrdca crystal « 172-173 Plate 17, 2 4 , (Crossed KIcols,X 360) u e z t u r e . . « » • • « . . . . . . . . . . . . . » . . . . . . „ . . . , , , . , . , » 174-175 Plate 18, K 4 , (Grossed Hicols,1 34) lexture . . . . . . . . . . . . . * . . . . . . , . " 175-176 Plate 19 , Y 29* [Crossed Sicols.X 34 ) iexture . » . » . . . . . • « , , > . . . . . . , „ . " 177-178 Plate 20 , ¥ 29 ( Crossed Eicols,X SO) Secondary coating of quartz c r y s t a l s . . . . . . . . . « 178-178 Plate 21 t 7 29 ( Crossed 2TIcols,£ BO ) Aggregates of kaolin!te » 179-180 Plate 22 , 341 A , { Crossed Uicols,X 34) ae^iui-e « « « . . , « . « . • » . , « . » . » - , : , . , , , , » . „ < . , , » . , » . w 185—188 Plate 23 » 341 A ,(Crossed 2!icols,ii360) Kaolinite aggregates »« 186-187 Plate 24 , 341 B, (Crossed Elcols.X 34 ) iexture « * • * ' . * » » . « < » . - • , 5 ! 190—191 Plate 25 , 341 B , (Crossed Eicols 360) Vermicular crystals of kaolinite . « 191-192 Photo grama • • • . Photograph of hand specimen ( about natural size } " 177 Photograph of ha®! sample of 341 a (2/3 n & t , & i s e i 1 0 5 Photograph of haM sanpl© of 34-1 5 fS/S rot.sis©} « iso motogeatfk sf hand «aqp*« :,8 4SP i f & l m I . « lis-isf Si&sesm. Z'igum I-Gsrtain change a In ratios « 199-200 Figure ii-ytsiativc ©ales .sad Losses . » . » . . • . , » , » » « „ » , IS3-209 Figare ^-Absolute Gains Losses # * • • » « . . * « • . . . « « • • « « 135-200 Keistive ctuisgus iz mlmf&l constitUsmtt;.* « 199-200 i mimziiim OP TAI ?O gBAsopioHtaa liSUL » 1 PC? g-UHODIQBtla Sagtple. V37A. a . Classification fla© rock represented by slide ¥374 and the corresponding chemical analysis shows the following characteristics? 1.Texture - holocrystalline, porphyritie. £'«AIineralogic content; M c r o ^ t e r , Analysis, Iform Calculation Quarts 23% Ortnocl&se 21',"-Plagioclise 40 Jo Hornblende, iiiotite J 14% i,ugite ' Iron ores.etc. 2p Botei- Tm fin©-grained nature of the groucdmase preclude© the possibility of aa icing a very accurate micron©trie analysis in this slide.lowever the above figures uere obtained from a very detailed straight-lino procedure -and,I believe ..my be consider-ed approxisiate Ly correc t.especially as they check the norm cal-culation so closely. The rock belongs to J loss 2 (d&rlc constituents between SJ: aM-SOf) Order 2 I t o AbsoAnggl „?aaily to SO&ftod Plfcg. to ori-hoclase 50J50 to 95:5) of Joh&nnsen's classification sad represents a a typical Biotite-bearing HornMenae' Sranodierite. Quarts SI .24 « Crthoalase £1 »GBf Albite £3 .057 Anorthite 17 Piopside 1 .67 ' Hypersthene 11 •2 O ihigne t i to 1 * 16, liSUL bolerosco-Dic ^xaaiination lecture - holocryst..lline,porphyi.-itic- sabhedral crystals, of plagioclase and enaedral crystals of quartz and orthoclase,to a fine-grained crystalline aosaie of quartz and orthoclase. ^jneralogical Composition (1) Plagi oclase-occurs its subhedral slightly el-ongate crystals (up to 8ranulong and 4mm. wide).Determined as oligocl&s -andesine.Has soarp non-corroded borders,with a suggestion of zoning' in places.Albite twinning is not well developed on the whole. Alteration- These phenocrysts are in a uniform st~te of high alt-eration,ofte 5; sufficient to obscure the twinning.Alteratlon products form a cooplox tiny flakes and fibres of a mineral assussd to be mica, intermingled with minute grains and plates of a mineral too small to be determined,but possessing the birefringence of kaolinite.So cal-cite ,epidote,or zoisite were observed. 12) Quarta-:;<nhedral crystals up to 7 ma. in dia-meter. Show highly corroded borders with a surrounding aone containing ssjall angular and corroded fragiaents of quarts with a similar optical orientation to the .as»in iaass,(See.Plates 1 and 3).These phenocrysts exhibit somewhat w»vy extinct ion,relievod in a few places by fractur-ing. Inclusions of apatite and rutile are present. Seraarks-It is evident that considerable resorbtiox;- of quarts has occurred aere f large - phenoorysts having been foraed.to be later attack-ed and replaced by orthoclase,leaving an intimate intergrowth of quartz and orthoclase as a groundmass. P L A T E N r J I.'F Q/Jorfe fe/berpocryjtf ctysf JZ - J/pyyfy/c/; pro//7S ejTiv/pws/? LTjmu/fo/Je&vs/y ft? ft/at-fA>e/?ocj-ysf, 1?/7c/. - (?rc>£j/7a//77<7&S' of a /77cvaSc of ip {sorfe V37A TA/ PO Gf?ANOD/OR/TE E'LA TE N°/ START/ALLY WEATHERED /4AG-X36 C/TOS3ED N/COLS liSUL (3) Orthoclase-a fev, anhedral crystals of orthoclase up to 2 mat. in diameter occur.Their boundaries are rounded and apparently uncorroded. Alteration-consists of a brownish cloudy ;aaterial containing a few tiny flakes of sericitel?) .Weathering has affected the orthocla.se aueh less than the plagioclase. Sroundaass ihe groundmaas consists of a raosaio of quartz and ortho-clase(avge• grain size 0.1 to 0 .3 ssa.) • in places thv. quartz extinguishes : simLtanecusly over a relatively large area® Alteration-less marked in the ground®ass orthoclase than in the orthocla-se of the phenocrys ts. Hornblende-apnarently two types present, i'ue first is common hornblende,anhedral in forat and showing pleochroisai in shades of green.This type is relatively inconspicuous in toe slide. She second type is paler in color„ less pleoch.roio ,anu possesses a fibrous formtappare & tly seconaar^ after augite,with which it is intim-ately associated in several plaoes.fhe optical properties of this variety would seeIE to place it as actinolite. Altorati on- s.ilration of these amphiboles lias re suite'! in the formatIon cf considerable chlorite,as we Li cs epidote c-v.nd iron ore. Bjotite - not common."hers this mineral occurs it hus a greenish-brow^ color,with a rattier" streaky,fibrous' appearance, ^nd high pleochroisia. " . Alteration-the earliest stages of weatheringTare evidenced• by "streaky" bleaching, aore advanced alteration gives rise to chlorite and liSUL and iron ore pv;hich form along toe cleavage planes in the mica. Augite- not common.A few subhedral crystals of augite occur,intimately intergrown wit a actinolite. alteration- alteration is to araphibole,chlorite ,epidote „and iron ore. . Accessory minerals g^afeite- small tabular inclusions in quartz. Butlie - needles in quartz. Iron Ore- not present in large quantity.Sone is undoubt-edly secondary,consequent upon trie alteration of the ferro-sisgnesian minerals. The general texture of this rocs is vreil illustrated in plate So, 1. This photograph (crossed Eicols,mag.>IS6) also shows the resorbtion border about the quartz phenocryst,as ivall as the advanced st^ge of alteration of the pIagiocla.se phenocrysts.Plate Ko.S,although intended, to Illustrate a more weathered sample of Tai ?o Sranodiorite,illustrates this resorbtion border excellently,in view of its higher magnification, (crossed Sicols,iaag.X80J. liSUL c .Chemical Examination 64 o 24$ A I 2 S 3 0.62% FeO Mg®, . . 1.37$S CaO la 2 0 2 . 6 7 $ % 0 -S^ fiSjB 1 .26% H 2 O - 0.09JS co 2 0.74$ Zr0 2 0.00% 0 . 15$ S 0 .07% Cr 2C 5 . 0o00% JinO . 0*09% BaO 99.73% The above analysis was made by Br.T.C.Phemister in the laboratories of the University of British Co limb ia . The following ratios appears A1 2 0 3 / S i0 2 0.20;: K 2 0 EagO / AloOs — 0 . 4 3 CaO / A1 2 0 3 — 0 . 25 • • • , 130 The analysis substantiates several microscopic observations which ••were madei. .. • . ' ' • . • . . . - . s.Ko zircon was found under the microscope 5and ZrO£ was not present in the analysis. b.Ihe presence of HgO in excess of that required for biotite sugg-ests the presence of secondary minerals*Chlorite c seric i te„and kaolinite were noted microscopically. c.The absence of calcite in the slide is checked by the absence of -C02.. d.Since S was found to be present sons of the iron ore noted under the microscope smst be in the form of pyrite® e.The presence of 3a0 would indicate that sores of the felspar,rep-orted as orthoclase ,v.'ill be in the form of celsian. f.J'he relatively large quantity of 2 I0 2 , in excess of that required for rutlie»:raices the presence ox some ilmenite imperative. This roclc,V27A,is considered to be the original type roclt' for the following samples? V37B,7370,and V212.The material at hand represents a slightly leathered granodioritetwhose aiost notable feat-ure is the remarkable resorbtion of quartz which is everywhere dis-played. • liSUL SAMPLE Y37B. A .GENERAL DESCRIPTION TEXTURE- LOOSE ,EARTHY ,ALLORIGII :AL texture GONE except I N so®~ o f the lumps. Color- light YEllowish-brov;n. Screen Analysis--Total Sample-15 grams 'Quartz Other p l u s 1 0 MESH 0 .79GIA. 0 . 3 1 4 G M . -10 PLUS 20 MESH 0 . 3 0 7 G M . 1 . 5 6 7 G M . -20 PLUS 4 0 MESH O.LOOGRA. 2 . 0 2 5 G M . -40 MESH L.OGAI 8 . 8 G M SOTE:-THE plus 40 mesh quartz DETERMINATION was made by hand-nick-ing the grains and WEIGHING THEM. THE minus 40 mesh quarts was determin-ed by a grain count ON SIZED MATERIAL under the MICROSCOPE. IN vier; of the INTIMATE INTERGROWTH o f QUARTS and ORTHOCLASE in the GROUNDmass HOWEVER,I feel HESITANT about ATTRIBUTING a great deal of value to this determination,since without a doubt ,ZNUCH of the fine-grained mat-ERIAL ^REJECTED In the plus 40 raesh PICKING,MUST CONTAIN a large prop-ortion of this GROUNDLESS quarts.The above figures are VALUABLE ,HOWEVER in showing the amount of QUARTZ present as PHENOCRYSTS. Determined % of Quartz -15/k In the rejected MATERIAL,TWO markedly different PRODUCTS,VSERE sel-ected from the mass of soFT,BROWN powdery MATERIAL comprising ITS major constituent.These had the following CHARACterIsTICS: a .V /H ITE ,EAS ILY CRUSHED• "PSEUDOAORPHS" OF f e l s p a r PHENOCRYSTS. (1) Practically insoluble in HC1. (2) Slightly aore soluble in CONC. HgS0A (3) Though soft and easily crushed has the suhhedral form of tha plagioclase pnenocrysts. (4) Almost free of lireonitie stain.. b.Bed-brown grains,easily crushed. {I) Becomes colorless with HC1. {2} Appears slightly isore soluble in Kg gQ 18) Contains remnants of ferro-magnesian minerals. liSUL b.IIicrosconic Examination Bote:-In making thin-sections of tais type of unconsolidated earthy material,I found necessary to select,for ray slides only the lumps,and, consequently do not feel that they represent a true picture,quantitativ-ely, of the minerals present.On the other hand considerable experimentat-ion has shown that there is enough of all the constituents present for qualitative determinations. ' ffexture-The section consists of one large phenocryst of quartz, surrounded by a ring of fine-grained material,in which a few 'ghosts' of felspar phenocrysts appear. 'Mineralogy ' ' (1) Quarts-large phenocryst.-of quartz(7mnu&iam) ,brolcen apart along original c:\acics and lines of wealcness,the fractures being filled with a finely-crystalline material,undo terminable,but from its birefringence ,assuraed to be lcaolInite(Eee Plate Eo.2).This crystalline filling is rarely stained to any extent,although considerable seal-crystalline linsonite is found along the margins and in-* incipient cracks in the phen-ocryst.The same resorbtion zone is found here,surrounding the iaain sass of quartz-. , As before the groundless contains considerable quartz tocc-urring intimately intergrov-n with orthoclase. (2} Felspar 'ghosts'- the phenocrysts of felspar have disappeared entirely,being replaced by a complex of secondary minerals.The follow-ing minerals were noted in this complex; .'{a}-. SiineralA-. Color— colorless Forra — irregulur flakes and plates of eatressly small sise. Cleavage—not definite.but appears in few in-dividuals where It is "mica-lilce". PLATE N'2 ft - fs-ocfore f///ec/ w/fih B - //?c/p/e/?f csocA- ra/77b//?-//7<? ///770/7/te. 7%/ PO GftAA/OD/OP/TE T£ C/TOSSED /V/COLS V S 7 S liSUL Belief — medium , .n greater than Can.Bal. Birefringence — lower than quartz in same slide = Extinction — parallel to the cleavage where Present,otherwise parallel to the direction of elongation. Thinning.— no twinning was noted.. ' ' Optical Character—indeterminate due to small 'Size of flakes. Orientation — crystals are length-slow. Bernards — this mineral forms a very conspicuous part of the altered p'nenocrysts. Bams —the mineral would appear to be. kaoUnite. (b)••Mineral- B Color ™ colorless Form — shreds and fibrous aggregates Cleavage — g o o d , "mica-like". Belief — mediums, n above Can. Sal. Birefringence — strong high first order colors ' but in places showing much lower colors9 even where cleavage 'traces appear.-Extinction — parallel to cleavage Twinning — no twinning noted. Optical Character — indeterminate as crystals are too small to obtain a figure. Orientation — crystals are length-slow. Hesarks -- common in the altered complex, lame.— except for the slightly low birefringence in soma cases the mineral appears to be '-.sertclte.- . • (c) Mineral C Color — colorless Form — occurs as a formless background to the • other-minerals® Relief — low,slightly above Canada Balsam and be 1 ow iraolinite. Birefringence — has a very lav? birefringence. Kams -- tills mineral would appear to he halloysite••« The alteration products of these- phenocrysts would therefore appear to comprise Icaolinite,sericite,and halloysite,with a few grains of the unaltered felspar remaining.In view of the work done on the so-called sericite from decomposition or felspars,the cost outstanding of which is referred to on page 172,of "She Kao!4n Minerals",Prof.Paper EO.165J£» U.S.&.S.'jr by Boss and Kerr, there ajjpears to be so as question as to • 134 • • • • - • • . • . . the nature of this mineral.Some "sericite",^'hen segregated and analysed •proved to contain only minute amounts of KgO^and appeared to approxim-ate the composition AlgOg« 2S i 0£. % G. In other words the mineral would be changed to lcaolinite (A1g0 3 .2S i Og.2H20) by the addition of one molecule of \?ater .According to description this mineral differs only from true sericite In possessing a slightly lower birefringence.The work of Kerr and Ross sight suggest that in the present case we are taking too much for granted In glibly using the term sericite.As a raatter of fact,froa its association with the plagioclase,it is obvious that the mineral must be,not a K mica,but one carrying Ea,such as par-agon! te. However vf& v/ill go further ana suggest that much of it nay well be "the muscovite-like icaoli); mineral" of Boss and gferr.and not a mica at all. (3}8rouBdaa.ss . The groundnass preserves its texture for the itsost part,alth-ough more highly stained than the original material. S-e •• . . . , v a.Orthoclase - This mineral is relatively unaltered in the groundmass as corapared with its phenocrysts.In places the alteration has been complete ,however, resulting in the formation of large aass-es of halloysite and other products.It is a notable fact that there is practically no truly amorphous material in this sample.Another interest-ing observation is the apparent susceptibility of halloysite,and even quarts and felspar9to staining by lisnonite as compared to sericite. and kaolinite. b.Ferro-.'iagnesian ilinerals-Mearly all traces of these miner-als have disappeared,their original location being roar iced by extremely heavy iron stain,somewhat pseudomorphic in fora,interleaved -Kith iron P £ A T £ A T 3 -fife. - (Pisor/z fifepocrys/' /?/7e/?ocrysf j^em - '(/fas?' <?/ T A / F O C f f A N O D / O R I T E C/fOSSED /V/COIS V 3 7 B liSUL ore,, considerable chlorite,and shreds of the original material.Chlorite is conspicuous throughout the -glide.not being confined solely to the proziraity of the altered hornblende and biotite. (4J Accessory Minerals -Apatite- is unchanged,as is rutlie,but it would appear as though BOW of the iron ore had been transformed to linaonite. e.Chemical Exaiaination S10, 62.90% A 1 2 0 3 1 8 . 1 2 % Pe.E03 5.89£ mo " *m% %0 ' .26% . 06.0 .04^ • • l&g© ——•. EgO ' 8.3S£ K^O 6,21% JJgG- .7 % m o ^ .-• \ «m% iZa The above analysis was made in the Eoelserfeller'Institute for Rock Analysis,Wisconsin. A1 20 3 / Si0 2 --0.2S K S 0 IFTGP' / M G O G — 0 . 1 9 • .. CaO / AlgO^ —.002 liSUL xiineralogic Calculation Quartz" 34.90$ Orthoclase 13„90£ Sericite 9.55% Ohlorite 0 . 73$ Xlmeni'te' • 1 Limonite & e Carbonate 0.23$ Alp03 .2SiC2 .Dihydrate 23.47J5 .Trihydrate 6.26 % The above calculation was made as follows? S. G was apportioned between Crthoclase and Sericite in the proportion of two parts to one respectively.This appears to give a reasonable percentage for sericite,, but under the microscope more unalt-ered orthoclase would seem to be present.This may be explained,no doubt,by the fact that soans of the sericite is in the foria of the "mus-eovite-like kaolin mineral11 before described,which in future will be referred to as "hydromica". Since the ferro-magnesian minerals have practically disappeared all the tlgO was attributed to chlorite,v?Jiich Is conspicuous In the thin section. All the PeO ?:as combined with 1'iO^ to give lineal te .excess TiGp . . . & W R being attributed to rutile „which is known to be present. All the FegO,, was combined with an eaual proportion of v.-ater to give limonite. OaO and 0© being present in equal molecular proportion,joined liSUL to form calcite. Three constituents,AI205 8SiCg 9 and HgO , remain to he apport-ioned.Since no amorphous material seems to occur in the slidetand since no diaspore or hydrargillite were identified under the micros-cope j,hyclrous aluminium silicates must he the remaining minerals ^ex-cess SiOg being in the form of quartz.As mentioned before itseems probable that the un i-hydrate is present {as hydro mica) ,but for the ' catee of simplicity only the dihydrate and trihydrate wsire calculated. • From the microscopic examination, these would appear to be Icaolinite and halloysite re spec tively. Hotveve r the calculation seems to give rather toohigh a percentage of "zaolinite,and it is not unlifcely that some of the dihydrate should be split between the oni-hydrate and the trihydrate,giving more hydropica and halloysite* If the above calculation is correct,only 1 6% of the AlgOg would be soluble»A1though no determination of soluble AlgG^ was made for this sample 9the above figure would seem to be a reasonable-one by comparison v/itn JHore weathered material for which the determination was made® -As was p o i n t e d out earlier„the quartz determination 9made by screening and hand-pic icing, is woefully inadequate for this type of rock. liSUL a.Semarfca . The accompanying photographs serve, to Illustrate several interest-ing points*Plate Eo.2 shows a fractared quarts phenocryst.in which the fissure has been filled by a finely crystalline material,assuaaed to be jteaolinite.lt also demonstrates the manner in -which limonite has worked Its way into incipient cracics in the quartz.Plate Ko.3(crossed Kicols. nsg,X80) shows not only the manner in which the quarts is. fractured but the resorbtion boundary about the phenocryst.'Throughout the groundmss will be seen numerous angular and corroded particles of quarts.showing similar optical orientation to- the main body.A *ghost* of hornblende is also included,consisting of a heavily stained area,showing original structure to some extent. In general the following paints should, be emphasized, withbregard to this • material* l.'Xhe sample represents an intermediate stage of weathering.Plag-ioclase has gone entirely,the ferro-raagnesian minerals are nearly oblit-erated ,> but considerable unaltered orthoclase remains. 2.2he orthoclase of the groundless is less altered than that of the •phenocrysts. 3.Practically no truly amorphous aaterial is present, although con-siderable halloysite occurs. 4.Plagioclase alters to icaolinite.halloysiteJsericit^'(paragonite or more likely hydromica) and a little calcite.Orthoclase alters to kaolinite,halloysite,and'sericite'(possibly true sericite In this case, possibly hydro sica,but apparently both).She ferro-aagnesian minerals alter to chlorite and iron ore in the extreaa case,augite first going through the stage of changing to hornblende(actinolite}.Eo epidote liSUL or zoisite "-ore observed,, 58The• coarplex resulting from the alteration of.plagioclase is ,in general„coarser grained than that resulting fro® the decomposition of orthoclaseo 6»'flalloysite seems to he stained by liraonite in preference to &aolinite»serieite#orthoclase and even quartz.Ike boundaries of quarts grains ^however,acquire a coating of liaonite while the felspars are' relatively unstained.via.*Iron Stained Sands and Clays",Jour,0eol.¥ol. XXXIT, lo .4 »SBy*tf«ne 1926 »p. S52,3ia©0arthy.»• . f liSUL Sample ¥570 a.Qeneral Description Texture-loose ,earthy materialman original texture gone Color-reddish-brovwn Screen Analysis-Total Sample - 15 gram plus 10 mssh -10 plus 20 mesh -20 plus 40 tnssh Quartz Other 0.525gm — — - 40 mash 0.654gm. 0 . SOOgra 0.200ga. 1.504gm 1.2 gai. 10.31 go Sote:-see the corresponding note for sample ¥373 Deter rained % of Quarts -16.5; Here again a white colored product %-as hand picked from this material .As before it showed a tendency to assume a crystal form^aith-ough less so than in V378,and on the v-liole was considerably softer.Ko traces of the dark minerals regained'.in this sample. b.liicroscopis imagination Texture -The original texture of the rock: has disappeared entirely in this sample,except for 'ghosts* of felspar phenocrysts.The section com-prises a complex of secondary minerals,and corroded quartz grains,in a relatively inconspicuous background of formless material of very low b irefr ingence • " . . . Mineralogy ' (1) Quarts - on the "/hole the size of the quarts grains has been reduced,the mineral occurring as small angular a.nd corroded frag-• P £ A T E M ° 4 f^/c/Zsrt? ///&>£fra/sog /fye /770/?/7er /'/7 yv/?/c/7 /fre <?/7e of o/c/fe/s/bc?/-jb/pg^ocrysfs /s ///pes p/s&rfz &T0/r<?/7 ///7es o/y/Z/ '/pe- p/sojrfs ' V37C TA/ PO GfTANOD/OW TE PLATE/V*4-CffOSSf/? JV/C0L5 X & O liSUL raents,which., in aany cases,extinguish over a relatively large area siasal-taneously. (2) Felspars - • Felspars have disappeared entirely from this sample,although their original presence is evidenced.by 'ghosts!,which consist of a compl-ex of unstained secondary minerals,in a finer-grained,moi'e highly stained groundmas3.The following minerals were identifiedt a.Kaoliriite - In general similar In properties to that described f rem V37Bdt forms a more conspicuous part of the slide ,however,than previously..partly due to the fact that it occurs in larger crystals,and pertly because there seems to be more of it present.On the site of the old felspar phonocrysts relatively large vermicular crystals smlce their appearance.Intermixed with smaller flakes of the same material and formless masses of halloysite.Plates 4 and 5 illustrate the type occ-urrences of kaolinite resulting from the decomposition of the pheno-crysts.These crystals mast have resulted from actual growth in place. Again the unstined condition of the kaolinite must be commented upon, in view of rather highly stained condition of most of the section, b.Sericite - on the whole the mica-like constituents are reduced in quantity when compared to V37B.There is also -nore material which In view of its lower birefringence.would seem to correspond to hydromica. in som places this material actually seems to be intercalated with Icao-linite ,apparently in the process of alteration to the latter mineral. c.Halloysite - occurs as a background to the aforementioned min-erals, it is without definite form of any sort,but exhibits slight biref-ringence. • fl4T£N0'S&. o/ •o/fe're'c//?/<?<?/& c/a>jre jt?/?eA?i?tr/-jAs/y /77t7/<rs-/a/AS // Vf/p o/ /fri? £i7c/r<?/-<s>6'/?a' /J- &/T& V37C TA/ FO GffANOD/Oft/T£ / / / G / / L f M / E 4 T / / E / T E O C/?0$S££? /V/COLS S 3 6 0 VJ7C liSUL (3) aroonOmass - the original texture of the grotmdsasa is eviden-ced to socu extent by tiny corroded quart,; grains.Kiese are set in a copies of secondary ainsralo*finer - grained and oor© highly 'stained than those occupying the sites of oli paonocryst3.?ractie,, ily no. arsorphouj aaterla* is seat, and neither dlaspore or gibbaito srorc founa* • UJfterro-iaugnoslBn 3|i*r*l»- ttte a&ris oosstlt touts nave disappeared ealthough their w ig iea i locations are caritod by d&rlt fibrous areas.wita which £>oao iron or« is oik-c associated. ; o.fijr e&o • ——* . KfigC — iae above analysis tsas sate la the TtoeiEe feller Institute far Bock • i-nalya is 9 ulscorisi su liSUL AI 2 0 5 / SiOg — 0.31 IS20 / — 0*05 Quartz 40„2£ Sericite IS. Ohlori to 0 .26^ liffisolts -Calcite 0»20# Limonite 6 .94$ futile OaCO^ AXgOg -„ 2S1C2 •Dihydrate £2•10& ts . " .Erlbydrate 14*36% ilia following procedure was followed in s ^ i n g tno above calcul-ations All tha was attributed to sericite in view of the highly altered nut-arc of this site rial-. -All the i!gO was attributed to Chlorite® Peg was anitGd with an equal amount of flog to form lls^nito.excess Ti02 giving rutile. fe^jOg was combined with an equal molecular proportion of Hpjj to give liraonite. 'The remaining AlgOrj.EiO^.and fig 0, we re apportioned to the d1hydrate and trihydrate.oxccss SiOg forcing quartz.Here again the a b s e n c e o f the h y d r o u s aluminium oxides .at l e a s t in c o n s p i c u o u s arnount . w a s ; p r o v e d by m i c r o s c o p i c exasination.fho d i h y d r a t e a n d t r i h y d r a t e l i k e l y r e p r e s e n t teolinito amS lialloysito.although i t seems reasonable i ) 141 t h a t som „at least,of the trihydrate ,as calculated,should be s p l i t b e t w e e n t h e uni-hydrate and t h e dihydrate to g i v e m o r e fcaolinite a s s e l l a s hydrorrhea,Then again t h e trihydrate is a s s u m e d t o b e halloy-site ,v.hereas t h i s minora!.although usually having the f o r m u l a A 1 2 0 3 . 2Si0 2 .3H 20 attributed to i t , m y apparently o c c u r with v a r i a b l e amounts o f v;ater,in view o f its metacolloidal nature Another f a c t o r to consider is the adsorbtive power of the colloids of Al 2 0 3 and S i O g with reference to 220.In other w o r d s some of the Z20 reported in t h e analysis m a y be adsorbed and not combined a s sericite.If t h i s is the c a s e some o f t h e s e r i c i t e m y i n r e a l i t y b e in t h e f o r m o f hydromiea. S h e a b o v e calculated mi neralogic c o n t e n t a l l o w s 2 8 ^ o f t h e AUG-, t o b e s o l u b l e i n t h e f o r m o f halloysite.By comparison with V212 this f l g -u r e W 0 G l ! i s e e ® t o be a l t o g e t h e r t o o low.This s a y b e e x p l a i n e d b y o n e of two possibilities j t h e f i r s t t h a t ¥ 2 1 2 r e p r e s e n t s a t o t a l l y different f o r m o f w e a t h e r i n g from ¥370,the s e c o n d t h a t a p r e v i o u s l y u n r e p o r t e d m i n e r a l , c r y s t a l l i n e in form,and having the sams formula as k a o l i n i t e i s present.The former s u g g e s t i o n I s s u b s t a n t i a t e d to sob® e s t e s t b y a ^microscopic examination; the l a t t e r l>y t h e f a c t t h a t b y c o m p a r i s o n w i t h a l l t h e o t h e r s a m p l e s for w h i c h s o l u b l e A 1 2 0 5 w a s determined,the f i g u r e o f 28/a still appears too low,and should this be true the generally c r y s t -a l l i n e n a t u r e o f t h e m a t e r i a l would preclude t h e p r e s e n c e o f a p p r e c i a b l e .amounts o f c o l l o i d a l m a t t e r . I 141 d. Remarks P l a t e H o . 4 i l l u s t r a t e s t h e t e x t u r e o f t h i s s a m p l e a s e x a m i n e d m i d e r low power (crossed Mcols,:; lag .SS ) . 'Ghosts' of felspar phonocrysts appaar as clusters of unstained crystals of kaolinite against a background of semi-cryafcallitte material. ' Plates Eo.jil and 53 illustrate the form of these kaolinite crystals, under higher magnification (crossed Ificols >; 360) . la general the following points may be mentioned: {1 Jjixcept for residuals such as quartz,rutlle and ilmenlte,all the constituents of this material are secondary. (2) Relatively large crystals of kaolinite are comparatively plenti-ful here,many assuming the vermicular form. (3) In places there appears to be a direct gradation from hydro mica into kaolinite in the same crystal. (4) Limonite has increased over V37B.while chlorite has decreased. •.Eutiie has been .slightly, concentrated. I liSUL Sarenle VS1B a.Se.neral Description Eexture — ear th-1 ike,loose 9original texture re-coved. Color — brownish-red Screen Analysis Sotal Sample — 15 grams p l u s 4 0 nash 1.79a gras. - 40 isosh — 2.633 gras. Eote - see corresponding notes to previous samples. Sfegascoplcally it was found possible to differentiate only between quartz and the reddish-stained.earthy material comprising the rest of the sample® -b.Microscopic Examination Texture -all original texture has been obi Iterated^he section showing only a number of rather sieall«corroded quarts grains set in a highly liraonitic.obscurely crystalline background. On the whole more quarts appears in this material than in TO7fl*It has rather feathery outlines which are due in many cases to the heavy liraonitic stain on the boundaries of the grains.In grinding the section ths edges of the quartz grains have been bevelled.resulting in a change of birefringence towards the edges of the grains which might easily be mistaken-for a secondary layer of quartz. 2he -groundasass is a structureless mass of lirnoni tic-stained material;in which vague and shadowy crystals may be faintly discerned. J Z 7 / ^ T E A / ° S 6 . Crysfc/s af ft? /-e/'tryr /-//spft/j jr/77o//<s-r jstc^ys/a'/jr sr/// <fjr/>l?e?/<7//y trff/re /o/p O /fr/c/isz-ts-. T7;<? <?/7/jra/sz?/>/ir TA/PO GffANODfOR/ TE PLATE A/°5b WGHL Y WE*A THE ft ED C/fOJSED A//COL3 X J 6 0 VS7C liSUL I n s e - e r a l p l a c e s a h e r e i r o n staining i s a l i t t l e l e s s i n t e n s e f l a k e s o f sericite m a y b e seen.Apart f r o m these a n d i r o n ore,no o t h e r minerals w e r e i d e n t i f i a b l e , in t h e h e a v i l y s t a i n e d complex.Some of the lirsonitio m a t e r i a l i t s e l f e x h i b i t s a f i n e l y - c r y s t a l l i n e structure and. may t h e r e f o r e b e goethite.One s m a l l c r y s t a l o f tourmaline was n o t e d , apparently residual from the original material. c.Chemical Examlnatjan SiCu AlgOg Pe202 FeG 2%G CaC Sa20 Z 20 V il20-Ti0 o S o l u b l e A l g O g - r -Solubie Iron{ as PegO^) 3 . 66 <,34/1. 16.73;?, &.70£ 8«23|» 'OA 0 6 59$ ' . 0064^' •0*07% 0 1 6 . 5 4 $ o f t h e s a m p l e 6*77$ « « All the fi0 2 was soluble. T h e a b o v e a n a l y s i s ? : a s made i n t h e R o c k e f e l l e r I n s t i t u t e f o r S o c k Analysis .Wisconsin. A12Q3 / SiOg 0.25 J 148' X20 / AlgGs — 0.03 • CaO' / .Al 20g — » -0,005. OalouAatlon of .iilaeralpgie Con teat Quarts 46.0l£ Orthoclase i . Sericite .. • • • . , Chlorite 0 • 1Z% idsiemlte - .. 7.64JE' Ilmenite • 0-,2Sjf Sutile 0,12% Calcite ' • AlgOg. 2S i02 . Dihydrate 28.S4J3 " • M .Trihydrate 1 1 <,20$ The above calculation was trade as follows. formally all the i£20 would be attributed to sericite in this type of raaterlal,especially since no orthoclase was noted in the section. If this m e done .however,the amount of insoluble £1 n wool* bevexc@®a-2 A ed.l'here is another point which night be overlooked ,however,and that is the power of colloids to adsorb XgG^von kaolinite itself-possesses this ability,Soma of the i%0 my,therefore,be adsorbed ,£nd not coablndd in a definite compound.However since there is no way of estimating the. quant-ity of i£2G held in this manner,all of it has been attributed to definite minerals® % C was all attributed to chlorite,as no sign of the ferro- magnesias : minerals remain. I 149: Fa© s a d S i 0 3 a o s o l o e d to f o m r a t i l e e x c e s s no2 forming r u i i l e , This a p u r e l y eonwjafcioaal p r o c e d u r e ^ s i c o © the f a c t t h a t a l l fchS n & 2 ^ f e r a i a M t o te s o l u b l e w o u l d s e e m to p r e c l u d e the p o s s i b i l -i t y o f r u t H e a t l e a s t b o i n - p r e s e n t e d f o r t h a t a a t t e r i l a s a i t e a s -well* - ' 6 a s det-e^alned by s o l a b i l i t y , w a s coatoiaed with-an equal mol-ecular o f water to g ive l i s o n U a . - ^ t i i e r the iron hydroxide pres-e t , f e e s t u i a f o r s s l a o r n o t i s a ^ y ® s t i o a a s l K e e a « h 0 l e s e r i e s o f t h e s e i s l a e r a l a e x i s t , ! * ^ i o U w a t e r i s a v a r i a b l e f a c t o r . H o w e v e r the p r o p o r t i o n a d o p t e d , 1 b v i e w & t t h e a p p e a r a n c e o f t h i s j s a t e r i a l . ^ t m l d s e e s to b s a reasonable -quo* O&O and e o 2 were un ited to for® c a l c i t e . In the above c a l c u l a t i o n i . I £ C g sad 3 £ 0 were apportioned between the dlhydrat© sM the tribydrat©^anfl in both-cases cosfeined w i t h T-c-assaite the trihydrate to represent h a l l o y s i t o , but there i s sons q u e s t i o n a s to w h e t h e r t h e d i h y o r a t e i s la t h e f o r ® o f c H a c h i t c . / l l , G , o ' O m ^ 0 9 o r the s i l i c a t e A l g 0 3 . 2 £ i 0 g . 2 f l ^ 0 B T h a f o l lowing r e c a l c u l a t i o n TOiu-asoKts t h e f o r s s r p o s s i b i l i t y ! Quarts • SO. C l i a c h i t e lfi .3££ H a l l o y s i t e . 1 1 . 2 0 $ The r e s t o f t h e c o n s t i t u e n t s b a i a g u n c h a n g e d . Several " factors ss&ai to mitigate against this p o s s i b i l i t y . Among t h e s e a r e t h e a p p a r e n t c r y s t a l l i n e o r s e r a i - c r y s t a l l i n e n a t u r e o f t h e Sroundnasa * t h e overly high f igure for quarts ca l lod for .which i s not s u b s t a n t i a t e d u n d e r the m i c r o s c o p e , a n d the f a c t t h a t t h u s f a r i n t h i s i liSUL notorial the h e r o n s aluainiuo oxides have ml appeared. Since nothing correspondfig to gibbsite or diaspore were observed ,eH*oer feere or in the previous samples it appears unlikely that they ocom^T&ls is further sa&afc&nUstod by tha Tact that all ths Al o attributed to tho d i s r a t e and the trihydrate rsast bs in a soluble S&e sarss difficulty that was pointed out with regard to YZ7C is now encountered:the di&ydrate mast, i f present ac a silicate.bo so is the for® of a crystalline sineral,with the sai© foraala as too U n i t e bat soluble- t» dilute acldvlf preaeat as cliachifco the solubility re qui resent will be fulfilled but -not the crystalline one. At present this possibility of a sew atnersl must regain isarely a posslbility..since without farther facilities it is impossible to undertake further study of this material. Oaly one photograph is included with this s e c t i o n e d that is intended to Illustrate ssrc-ly ths general texture.Corroded asd alar fr&gsan&s of qa&rta are oozsaon.against a hlgialy stained ani obscurely anisotropic background. Jfee following points should be emphasized: {II Ifirnonitic stain i s sore dense in this sample tiisfi in any prev-iously studi -'d.tThis is due *not only to & higher content of Uaouit© but also to Its wore eves distribution. (2}Here i» V3?B.0ad is retained,in ths form of caloita,relative to JTagO»although in gunoral it proves more soluble than the latter. liSUL I SI AltHo^i the calculation would see® to i ^ i y the necessity of some orthoclase r e ^ u a m t S 0 E B ^ M is held in an adsorbed state.toothy a c t i o n Is that a p o t a s s L ssilite is p ^ t . i n v i ^ of .the fast that « « * * a i w m f l a g been r e p o r t e d that oolites are not usually associated with the B e r i n g of this tyPS of ^ i t aspe.r. to he , additiono -(4) Practically no a^rphcms mierial is preset in the section. liSUL and ConeInsinna IsMMMZ Pour sarsplos of fai Po Granodioriie •were available for study; Y3TA - specimen of fresh rock ¥373 - partially altered V37C - iiigily altered V212 - highly altered _C.ha.rae. toristioa fexfcuret ?57A - ho 1 oc ry 31 a 11 i ue 9 por phyr i t ic -YS7B - loose , luany ,earth»lilK aafcerial,texturo sosowfcat In so.-Ki- of tile lu;ops» ¥370 - as for 7373,except that tho are eanllor and texture . - gone. ¥2X2 - similar to 7370 "0ol©sr j • . - "grey . • 7373 - baff ¥270 - light reddish-brown 7212 - light brownish -red Screen Analysis? there is an Increase in the relative proportion of plus 40 sssa qmrtz^wdta m accompanying decrease in tfes else of «rrafe<* in going from ¥373 through V37Q to ¥212« ' ~ •JigMsajgaoMaJ^Bto&tJjm V37A - hoioer/siaUiae por^ritic-snbhateil crystals of -ola^aolase and anhedral crystals of quarts and orthoclase,in a fine grained ao*aie of qmrta aai crthoel&ae.Darls ajiaerais not &bunaant,ccr,sist of iaoaabi en*® with subordinate aeglte and biotite.Rooic is s l ightly roathsred ,chlorite , antphibole,kaolinite,aerie ita being present. ¥378- original structure preserved fractured and ersefcs £ n i 0 a -cita 30G3 finely crystalline material.Only'ghosts» of felspar phenccrysts reasain,xaad® up of & coaplex of serlc it© 8 f Ine-graineS itaol i£i to , &nd fcatloy-site . Srouoamas tsore highly stained t h m prevloualy.orthoclaae i s partly altered , Ferro-mfweaian lainera'U almost eorajlotely altered to chlorite .sad Iron: ore* ^ 737G - original texture evidenced only by corroded quarts graios and Sftbsta* Of the felspars.2hese *ghosts* ere raarUed by ak unstained complex of relatively large crystals of kaolinite(ver^cular and fiaicyj c m hailoy Bit©»SoE8.'sericite' is present-Iron stain abundant over o M grosndsass, especially .so on sites of old "feialcs"0 liSUL V212 -original texture gone„iron stain "using overyvuiere present* corroded grains of quarts occur In tills bacitgrotmdev.hieh is. obscure iy anisotropic thrown the stained aasko , ?37S fS70 VZU 64.24$ 8S 62.36% G6c AlgSg 14c 18 y<; •• C J i^j-C 16® Feg02 0.6£;I 5 .mf, e.sojc 60 77:; Fe§ 5,83£ 0 Oo il/i iigc 1*37% 0 0.£l£ Do CaO 3&&Z.M 0 0„0Q£ 0 . 06;; 0.67$ 0 0«00j£ Qe oo£ £20 3«6S£ 5 » 56 jl X Oo fi^O £ © 7.S7?; 7. 04£ e2g~ 0*09% 0 Qo&&% 0 . 64 jC OoCh%: 0 9 X0)4/ 0,10$; T 0, 086)5 Q»8B% 0 . 90£ o . i5£ s • . 0e07£ UnO 0.09$ ' BaO • •• .... • • 39*75% 99, .70% 10Co02$ • 96£ f s m Quarts 23£ Crtho. 21> Plag. 40^ Ha*bifida 3ictite i ituglte 1 Iron ore < J S " V373 .. ?3?f; V21Z -Guarts 58$ Quarts %ta&rts 45o0ir Crtiic a Serlcite 8.90% Crtho. 1.87% Serial fce IO.SI;. Chlorite o.s6£ Sorioite Chlorite ilnc-Ri'te Chlorite 0,7of! tXmnltn XelilJjS iratile Msoiiite 7 s fj Butile Oalcito Ilnsaite 0 0 23/:" Mraosiie Maoist is Bailie Carbonate Oalcito 0.14J? -22.10% -.i'rihyd,- — — "i. X © SO />. "j! Several diagrams sad graphs are inciuaUsdelllastrafcive of progress-ive changes resultant upon the weathering of this rocit , . i g u r e I illus-trate a the relative percentage changes of constituents*in the four sasp-lee,VS7A holeg considered the original of the oters , {£«© next page I I Figure Jto,2(twlowi shov;s ti» prograsalve congas in certain ratios of cons t i tuen t a , dor L t Jw weathering of this r&cit. Figar^ £ •'I gore 3 rigure 3 illustrates the absolute change i» constituents ,duric- the weathering of 737...through V373,Y370,to V U Z . A l ^ was a w w d oowtirt to bring this about,the other analyses being raSalculated on this Of course -120 has undoubtedly undergone solution,but in general in this type o? weathering It Is the least subject to removal and thus gives a comparative idea of the actual iosses and gains undergone by the constituents of th& rock. 5 • Figure 4 \ liSUL Figure 4 illustrates as far a© possible the relative increase ana decrease in the minora! constituents of MZ7& goring- the weathering of tiilXS X'OClCw 7 5 7 3 ar23 7 3 7 , 5 represent successive stages in the alteration Of V37A.V212 apparently has followed a slightly different course than the foregoing nsiteriril,during its weathering, feathering first affects the plagioclase.,which breui® down into 'sericite%kaolinita,nM talloysito.as well ae a little calcite.In this material CaO is retained,in the for.-r, of calcite,relative to Ra20.2he 'sericite* is obviously not used here io its trrne sensevie.secondary afceeov-ite,but refers to shrodded fibrous aatorinl of fairly high but variable birefringence,possibly parsgonite.bat re-ora likely the "muscovite-like kaolin mineral'- of Boss and Kerr.Kaolinite -is present tin the early stages of wea-thering,as a fine-grained coaplex.As alteration progresses larger crytale many exhibiting vermicular for^are found. It wouH appear,in places,as though tho'sericito' was actually la the process of otenglug fco kaolinite.Halloysite forms a comxm background to the other mineralslShoats' of the plagioclase phenocrysts appear oven in the highly altered sample V37C.These 'ghosts' are "a^e up of consistently larger crystals of secondary mine rale, than those found ia the groundless.1'hoy are also less susceptible to H a m * tic staining than the retraining material. Orthoclase is relatively frosh.in sow p l a c e m e n plagloelase has praotic&lly disappeared.It also persists until a fairly high stage of alter-ation has been reached ,althou:& none is present in m c . l n the early stajus orthoclase presents a cloudy brownish appearancetard small flakes of sericite liSUL occur airs' tills e a s e it is f e l t t h a t t r u e s e r i c i t e d o e s r e s u l t f r o m the •weathering o f orthoclase a l t e r a t i o n i s c a r r i e d further.the f e l s p a r orealcs down i n t o a coaple;-: o f fine-grained Icaolinite,sericite,and hall-oysi te,as before.The a l t e r a t i o n p r o d u c t s .however,do n o t seem to a c h i e v e t h e same s i z e s a n d c r y s t a l form,as they do w h e n resultant upon the b r e a k -i n g down o f p l a g i o c l a s e . T h e s a r l i e s t s i " i l s o f t i le decomposition of hiotite a r e the b l e a c h i n g arid c h a n g e i n c o l o r f r o m brown t o green accompanied b y d e c r e a s e d pleo-chroism,as w e l l as a c h a r a c t e r i s t i c siraafey appaarance between crossed M c o l s . A s a l t e r a t i o n p r o g r e s s e s chlorite i s f o r r n d a n d I r o n o r e is liber-ated, of ton a r r a n g i n g i t s e l f a l o n g c l e a v a g e l i n e s in the biotite.fhe final p r o d u c t s o f t h e proeess a r e c h l o r i t e and I r o n o r e . H o r n b l e n d e l i k e w i s e g i v e s rise to t h e s e m i n e r a l s a s a l t e r a t i o n nrod-uot.Sc . A u g l t e g o e s t h r o u g h a n intermediate s t a g e o f c h a n g i n g t o a n a m p h i i o l o . p o s s i b l y a c t i n o l i t e o r a v a r i e t y o f f i b r o u s h o r n b l e n d e , b s f o r e f o l l o w I n g t h e c o u r s e o f t h e o t h e r s . S h e f e r r o - r a a g n e s I a n minerals,in g e n e r a l , a r e more r e s i s t a n t to d e c -o m p o s i t i o n t h a n p a I g l o c I u . s e , a n d p r o b a b l y s l i g h t l y l e s s so t h a n o r t h o -clase. Figure 4 g i v e s a r e l a t i v e I d e a o f the r e s i s t i v i t y o f t h e s e v a r i o u s m i n e r a l s to w e a t h e r i n g . A s d e c o m p o s i t i o n p r o g r e s s e s further.chlorite itself i s P r o l a n up, t h e c o n t e n t b e i n g r e d u c e d w i t h r e l a t i o n t o A l 2 0 3 , S i O £ , a n d e v e n lizO. T h e m o s t o b v i o u s c h a n g e d u r i n g the process of w e a t h e r i n g i s the p r o g r e s s i v e i n c r e a s e i n the amount o f c o n t a i n e d HgO.This i s accounted f o r b y t e n d e n c y o f more h i g h l y hydrated m i n e r a l s to be formed a s a result of o-156: more advanced -aeatherins.Another outstanding feature is the increase of limonite as.feathering goes on. The mine.ralog.ic calculations for samples VZ7Q and ?2l£ ^ 0 uld seem to require the presence of a .mineral with the formula of kaolinite,but unliie kaolinite soluble in dilute acid.Ko microscopic evidence v,a forthcoming to support this.and without additional facilities , it seems impossible to go into the question further, Various other features,mentioned for the most part in the body of the chapter ,present themselves.The only one which will be dealt with here is ttet of selective staining.It is not-able that Haolinit© does not appear susceptible to limonitic stain,sericite being only slightly lees S O o 0 n t h e o t h o r halloysite shows a tendency to be quite highly stai-ned,as does orthoclase,and unaltered pl«gloclase.Quarts is usually found with a lisonitic coating on its margins,and In and along cractes and incip-ient fractures. Before closing this chapter .mention should be made of the undoubt-ed solution of quart-/, evidenced in this material during the process of weathering.As shewn by screen analysis as well as microscopic examination 'phenocrystalline* quartz undergoes considerable reduction in average size in going from V37A to 7370 and 7212..Additional proof Is furnished by the unaistateable corrosion of boundaries which has occurred,and which is shown particularly well in?212.In no case res any Indication found of the deposition of secondary quart::. PLATE M°>6 A/ofe <Vfarfe gs-a/spj ere a^/-/"Pft/^ore. r^e o^j-czjs-e/ycrysf-o///y?e a/ /s oA^^e/?/ eye/p /fr^tsip/? //retreats}/ /v&j-Zr ///rr -o/y/Z/c- s/a/zp £/a TA/ PO CPAA/OO/OP/TE TE A/°6 CROSSED /V/COL5 X 34-QE&PSES FOUR i m g m t g s OF HOSG KOEFT Qft&JXSSS 157: Hong Kong granite - Sample K 1 a. . Classification The type rock {Hong KongSranite) ,as represented, by the thin-section XI and corresponding chemical analysis,has the following charac-teristics s (1) Texture - holocrystalline,hypidiomorphic,equigranular. (2) Composition -Microaster Analysis Korm Calculation • Quartz SI.2% Alkali Felspar43.6$ Plagioclase 22.8^ Orthoclase 29.57$ Albite 27.56% Anorthite 5.36$ Quartz 31.04)1 Biotite ) 2*2'/i Hornblende.) Corundum ,04% Hypersthene 4.02^ Magnetite .76% IlsBnite .47% Pyrite ,18%> Apatite .13% This rock belongs to Class 1 (leucocratos 95$ or over},Order 2 (Ab9An to AMn),Family 6 of Johannsen's classification,and represents a typical biotite granite. 158: tuHlcroscoplc Jsxamiaa.t-1 nn • • Megascopi o. . The rock is light grey to pin', in oolor and.has a h o l o C r y s t _ alline.hypidioraorphic.equigranular texture (avge.grain size 2 ram.) Microscnpl g -^Siaerals •:•,• : " ( 1 ) Q a a r t " • - 0 c c u r s a s r o ^ d e d grains and fillings b e t w e e n other crystals.The boundaries are smooth and rounded Extinction i s wavyanclus-ions of lath-like apatites,minor quantities of rutile.and bubbles are ~ present. • ^ - ^ S l M e ^ m o r e c l i n e form the major rock components. Orthoclase exhibits Mcropeg^atitic interSro*ths of quart,.arranged radial-lly about *any of the ^Jomcontacts of these minerals.Microcline is com-monly found intergrown with albite to form aicroperthite.Apatite crystals are frequent inclusions in both felspars.Alteration is to a brown cloudy product which affects .apparently,alMte ^ore strongly than either of the other two alkali felspars. (g) Pla^ioclase - v/as determined to approxinste oligoclase.Slight zoning is not ice able .Alteration is iaore narked here than in the previously mentioned felspars and comprises kaolin,sericite,and epidote. 14). Ferro-Hagnesian M i n e r a l s Biotite - forms the most conspicuous coloured mineral in the sect-ion. It is the common nsdium-bro^ variety commonly associated with granites and exhibits strong pleochroism and subhedral form. Hornblende - light green fibrous variety occurring sparsely dist-ributed through the slide. PLATE M® 7 Te^fvre of ao cA ff/jfi&Z-S HOA/G K O N G GPAA//TE PLATE EffESH FLA/A/ UCMT 159: .-iteration - Doth minerals, show slight evidence of alteration. •The biotits is sor^hat bleached and chlorite and iron ere have been re-leased. Secondary products resulting from the hornblende are chlorite and iron ore, ,_4cce ssorvjilinorals Iron Ore - is common in this rock Apatite - occurs as inclusions in both the quarts and felspar. Eassgp The included,photograph illustrates the texture of this rock f Plate 7 ) . 160: iojJaksaioal Ssaminatiou An analysis of this rocfe shows the following composition* S"i0£ 73,37,1 A 1 2 G 5 12.86'/; 0»53?t _ '2 3 2,37/t 0 .26^ l.lfijC 3 .26* H2 ° o.ss;C - o.oojs 0.00£ 0.21/t 0.00^ p£°5 ' 0.04% o.oo£ s 0.10,C 0 ^ 0 3 O,gq£ SiO 0.07/^ SsO 0.01& 99.69% - Sse abate analysis, was mde by f ^ . Pheaister in the laboratories of the University of British 0olaslJia» . the presence of SaO would suggest the occurrence, in th|a roclc of minute quantities of Celsian. A1 2 0 5 / SiOg ~ 0.17 % D plus Sag© / MgOg * 0-.&S OaO / A1S&S Q*08 161: .Saaole K S Texture t - fine gravel-lite material Color : - cream to buff Screen Analysis s 15 grams material iaasis Other 1 .83 gia. plus 10 wash 4 .49 gm. -10 plus 20 mesh 1 .86 gm. 2.*86 £ £ -20 plus 40 gm. 1 . 06 gm. 0 .50 im. - 4 0 813511 2 .30 gm. 0 .40 gm. % Quarts — 48% quarts Eote: -la view of the equigranular texture of this rock,I feel that considerable confidence can be placed in the above quart, determination. In general this m t e r i a l consists of angular and highly-stained quartz grains.intermingled with ^hite-coated felspar crystals and fresh looking biotite. P>£ATEN/a'& SfofAoc/<7<s-<? /S /t/pfi/y a/Zero's; ff>/s ccj-e, yr/7//c? arZ/pcc/cj-cp x> A?V<7f/><?/y /><«= HOA/CKOA/C CtfA/V/TE /=>L4T£ /v° 3 SL/Crtri r b/£XTH£mO C/fOSSSO /V/C0LS ' ' 162 (aJ-MiCroSCQPln fiyanijnot^rt feture - in general is unchanged from the fresh rock. Mineral Descrinti rm {1} Groartz-Apart from the marted tenancy for the bounSaries of quart, crystals to bo coated « t h a U T O , U i c stain.tfcere M s been no aP I»rent Changs in this ainera! . I t is i n v e s t i n g to note that this iron stain to favor in preference to other S e r a i s p r e s e n t s evidences of solution w r e noted. (2) Orthoclase and mcrocline -In Places these minerals reniain practically unalterod^hile in others they appear to have gone over.al.ost completely ,to a cobles of secondary .dnerals.lt is notable that where *icroperthite is affected the alhite intergrowths are nruch ,ore heavily fathered than the enclos-ing Mcrocline.'fhe reason for the advanced alteration of son* of the al*-ali felspar. ,Mle the rest renins a l ^ s t fresh i s „ot at once apparent. it is rerae?abered .hoover,that the section represents one of the grave i-liico lumps apparently resultant acre upon ^chanlcal disintegration than upon c h e ^ a l action,and that for the .ost part,the highest alteration is found around the nargins of the section,the explanation „ould seem to be found in a weathered shell or .one about each of the lumps. Alteration seeos to be so-^hat directed by cleavage and fracturing. In the section examined no determinable plagioclase «as found .As was indic-ated in a . .plagioclase is n^re rapidly affected than the other felspars.and B a y 6 l t h e r ^ b 6 e a c o a Pl e tely eliminated from the "grus"-like l u ^ s f.hich represent only the more resistant minerals.or may be so conxpletely disquis-of /y/crt?c///7e'/9/6/Ze - c/feraf/a/? of >9/£>//& /77ore /MVS HONG G/fA/V/TE PIATE SUGHTLr WEATHERED C/TOS5EP Af/COlS X 3 6 0 163: ed as to be completely indistinguishable. Alteration Products of the Felspars — Felspar alters to a fine-grained mosaic of minute grains.made up of the following minerals, (1) A few frag-nts of unaltered orthoclase are to be found in the complex. {2} In several places rounded and corroded quartz grains are seen in the mosaic,where these were observed.it is interesting to note that they were in close proximity to a large quartz mss and extinguished simultan-eously withit. (5) *he maa of the alteration material consists of sraall tabular grains having the following observed properties: Color - colorless to pale yellow Form - small tabular grains .showing a slight tendency to exhibit a stubby lath-like form. Cleavage - none distinct,in places its uresence is question-aole.if it i S present it is parallel to elongation. Belief - radium, n greater than Can.Balsam. Birefringence - comparable to orthoclase.with possible a ten-dency to be slightly higher. Extinction - indefinite clue to waviness.appears very nearly parallel to elongation. Orientation - again rather indefinite.but appears length-fast Optical Character- Impossible to get a figure asxmaterial too •small." She above characteristics are not particularly diagnostic for any known.Mineral.The form,birefringence.and optical orientation do not appear to fit kaolinite.which might easily be expected here.However,as none of these properties were satisfactorily determined in the section,and as this J°iATEN°/0 f?/test?//<?/? r<?^7/t>/e''f fr<?/7? fe/sf?&/-/?7sra //? a> fs/y^/y eryj-/i?/f/"/7£>/77<?ss of /fac?//'/?/ft? frj S/?/77<? fs f>rese/?f /VO/VG AfO/YG G/TA/V/TE PZATE/V°/o SL/G/SEL r W E A 7 m m 7 C/T0JS££>/y/COJLS X S G O K 2 P £ A T E N ° / i rf/fffraf/o/p cc/77sApcyy//po fsvy fo^/c,,- cryr/b/j- /rcf/-rV tys/* A^^/e ^ ^ ^ssTy^z/sc- s-Ti?//? a/-/ A W i XO/YG G/TAN/TE fid TEW*// SI/G/-/TLY V M m E f t E P C/TOSS£P /Y/COL3 xeo nm • 164 , this set of properties does not fit in with any other mineral which might be expected hereto will term U , i n vlev/cof the corroborative evidence aff-orded by the chemical analysis,kaolinite(?).Incidentally illustrations in the rtKaolin Minerals" by Boss and Xerr*,shotv Kaolin v,hich resembles this material sonsvrhat in form,and a f o re ire n t i one rl, ol t ho ugh this form is riot one commonly taken by kaolinite , it is known to do so. - fhe..Kaolin Minerals - T7,S,G-.S. Prof.Paner 165-S.1951*- Boss and. Kerr Several other rather Interesting points are worth noting in regard to this material,There has been almost undoubted replacement of quartz tbe secondary coraplex.'ihe evidence for this is afforded by the isolated grains S§ quartz, found In several places In the raosaic near to large quartz masses,and extinguishing simultaneously with them.Another place was noted tfoere the complex had apparently penetrated into a quarts crystal and al-most cut off an "island". (soe illustration) ^ In the vicinity of fer r o-sagaeeian minerals,a peculiar series of parallel lines,narked by iron stain.occur.?o explain these it is suggested that alteration affected the biotite before the felspar,11berating limonite ,v?hich was deposited along cleavage planes in the felspar.Later weathering of the felspar resulted In the formation of the the secondary conrplex,,with-out destroying this original structure. (4) Several places,for the most part near to altered biotite crystals, contain conspicuous amounts of a flaicey to fibrous mineral.with mica-like cleavagefbirefringence varying from yellowish-^hite(1st order) to blue{1st order}..and parallel extinction.These,as well as other determined properties would suggest this mineral to be the one p o p u l a r l y called "sericite" . It is obvious .however, that the birefringence is definitely too low for true fl4T£M*//£ /?/?<?rt?f/0/7 ro/TPyb/fs -Z/7e quertz Ms re>/>A?<re*£/ Mom /roAfc $ m w r g PL4TF //°/£ S / / C / / n r W£A T//S/T&0 C/TOSS£JO ///COLS X J 6 0 jo I : •••'••.:,-'!ii • .:•••• ' ' 165 ' sericite in most cases,and this,coupled with the fact that a number of these crystals show intergrowths to a mineral of lower birefringence(kao-linite) Ytfould suggest the transitional "muscovite-litoe icaolin mineral" of : i Eoss and Kerr*. fferro-Magnesian Minerals ••i Motite Biotite is the only ferrc-sagnesian mineral appearing in this section,It has changed in color from the original brown color shown in El to a dark streaky green,and is less pleochroic than before.in form the original biotite has altered by losing its definite crystal form asceviden-ced by cleavage and assuming a somewhat fibrous structure.Slight amounts of chlorite have been released.In general weathering has not affected the biotite very highly in this sample. General. . . 2he slide is comparatively free from linsonitic stain.On the -whole alteration has been of secondary importance in the breaking up of the orig-inal granite,the material represented by sample &2 being a typical^grus". - Remarks She following illustrations are included.Plate 6 illustrates the texture of the rock and the manner in which alteration occurs.Plate 9 is included to show the differential weathering of albite and orthoclase in microperthite.Plate 10 illustrates replacement of quarts by the secondary ®atrix.Plate 11 shows the peculiar stained lines in the complex. a ' - " .••'•. . . 166 . ' ' • . (c) Oheaical. SxETsinstlow i. chemical analysis of this material is as followsi SiOg 72»m% IS.19'6 % © GaO — — " ' • 15/1 • f W 2 She above analysis was sc.dc in the Socksfeller Institute for Soc& Analysis at I'/isconsin. AlgOg / SiCg ; 0 .E1 plus m M 0 / AlgOg - 0 .28 cao / Ai2y« — o.oo .Calculation of jglnerajLo^ic Qont,(,^ t. Since,in the case of this sample,it was felt that the quarts determin-ation ??as of sigaiflceut value ,3-afflc ten fc Si0 5 was alloted to quarts to tmi® op the requisite 4S£. itgO -eras all attributed to orthoclase and cdoroc 1 ine,escept for a very ssall proportion silo ted to sericite .Although so-called sericite is very, conspicuous in places,lt;veuld appear that in reality very little true ser-icite is present.Only enough XgO to form betvfeon lj£ to 2% sericite was taken. SaoO was all calculated as „ _ . aloite.apparently the foraof weathering' found here has not produced paragon!to,in any quantity at least,for only a small am-ount of m.20 reaains in this oaterial.T.'ithoufc question soia> unaltered slbito does rezsain and consequently all the U&^o ls attributed to it . if ,r ,ii ( 167: Hypersthon* was calculated &s the feraic.not for Hiineralogicel reasons, hat because by so doing the proportion of--other minerals Is not greatly affected,and the blotIto.which is the sain "dark" ssineral In thi* sample ,possesses an ucicnosra composition. Lioonite.ilaasite.and aider!te were cale aletad in thy usual manner. She disposition o f the regaining 4l 2 0g ,Sl% ,a»S % 0 was based largely upon aicrcscopic deterainafcion.2hese proportions are at best only appros~ iiaafee and arc intended to convey only a general picture and not a definite nineralogicsl result. ' kaoliniteI?} foraad the m a t conspicuous secondary mineral present. Apart from hydroasica.co other alteration product seems to be a conspicuous, : j compounds as definite hydrate3.First of all SiC2 and Mg-% wore united with . 1 water to give the Alaydrate kaoliaite.ls excess of m A «ater'rea»lm& !which would 'establish, the necessity for the presence of gibbsite,since this is the only hydrate usually forasd by weathering.It was found however that _ insufficient water was present to give the trihydrate.Xaolinite was now ; | recalculated,allot ting sufficient HgOg and SiOgito hydro si ca (Al203.2G102. 1^20} to reduce the «ater content sufficiently hers to allow of the formation of gibbslte.lt thus found that these three constituents could be calcul-: | exactly without any excess . It would therefore appear that considerable weight could be allowed to this ealcula tier,. The results of the final cal-at least constituent la vies1 of the kaloarystaliine of tho secondary couples,and the absence of amorphous material,it is possible to calculate the aluoinium dilation are given below; 168 Orthosis0© 2b»Q$ Sericite l.s'/ Albite 0,$% Hyps-estnese -Liaoni te 1.25$ Xisenite • 0.30;* Sidarito Saeliaite ? .4& Oib'osite _ J,*?ti _ • file above list of constituents appears to be substantiated by micros-copic exaa&natlon.except for the presence of gibbsite .which was cot dot-.eoted«Ag was pointed oitt,iios»8wt'»i»ea describing kaoliaitef-?! ®any of the !B0St' diagnostic properties w r s not definite. - With the jtraeae* of gibbsite a c c e p t e d i m r detailed microscopic exatalnatiea of the weathered complox ^as undertafen to try to ia©ati# this mineral.On re-e»uninatio» there appear® a distinct .possibility that •two aiserals are pre seat in the complex, both sofflrafcat similar in form bat one exhibiting a tendency to sho* higher interference colors and inclined,though m m & m t -vfavy .extinctlon. JfeaaE&L 111 Is the formtion of this material disintegration has been aare ji - . Iij active than cheaic&l decomposi t ion .resulting in the production ©f a ,1 "grists*. | J W ^lagioclase- has been entirely altared.no OaO remising in the ,[ saiaple » Or fchos las© and aiorocline have -altered variably .depending .pre-SQH&bly upon the ease with which percolating solutions could act upon the a.£lbite,forming the aicroporthitlc intergrowths -with oicrocline so ii' . coiaaon he re.has weathered sore highly than the other felspars present. i _ 169: (3) 'feathering o f the felspars .has resulted in the forsaation o f gibbsito a s well a s too 1 i s i t o * I n p l a c e s an unusual structure i s present; j definite lines .heavily stained with llsonits,run through the altered c o a p l e X j O B e a c h s i d e o f w h i c h a r e f o u n d c r y s t a l s o f g i b b s i t e . ? . h e r e s a t -; e r i a l h a s b e e n p l u s u e d o u t i n m & l a g t h e s l i d e , t o w a r d s t h e e d g e s o f t h s Ai' a u c t i o n f o r i n s t a n c e , a r e g u l a r f r a a s s w o r i c i s c o t s s o n c o n s i s t i n g o f a l l a » a -l,i i t i c a r a c k ; v / i t h a r m o f g i b b s i t e c r y s t a l s o n e a c h s i d e . X h i s s t r u c t u r e i s , a p p a r e n t l y s o s e w & a f c s i m i l a r t o t h a t m e n t i o n e d b y B l m j i n s p e a k i n g o f l a t -,i e r i z a t i o n i n S i e r r a L e o n e * . I n t h e p r e s e n t s a m p l e i r o n - s t a i n i n g h a s a p p a r -e n t l y o c c u r r e d a l o n g t h e c l e a v a g e c r e e k s o f t h e f e l s p a r , f o l l o t ^ d b y & n I:! a l t e r a t i o n o f t h e f e l a p a r i t s e l f , f r o s t t h e s e c l e a v a g e c r a c k s i n w a r d . r e s u l t -i n g i n a r e c r y s t a l 1 i s a t i o n o f g i b b s i t e a n d k a o l i n i t e . 5 f' ,:; I t i s t o b e n o t e d t h a t a l & r g © p e r c e n t a g e o f f e r r o u s i r o n i s p r e s e n t i u t h i s c a t o r i a l . T h i s i s a n e x c e l l e n t i n d i c a t i o n of t h e r e l a t i v e l y o n a l t e r -;l o d n a t u r e © f t h e r o c & . | H I fact t h a t o u a r t s g r a i n s a p p e a r , m j g a s c o p L c a l l y . i a o r e h i g h l y stain-I ;ij e c i t h a n f e l s p a r . s a y b e l i k e l y a c c o u n t e d t m b y b & e i h g r e r o f a l t e r e d i s & f c e r -J i a l s u r r o u n d i n g e a c h g r a i n , w h i c h i t s e l f i s n o t p a r t i c u l a r l y s u s c e p t i b l e t o I l i a o n i t i c s t a i n . 170: %ms>le g festtir© * - earfc&s.leoseipereo» material la t l ic i *U-«vMtMB« o f o rigiaal textare has iMailsfasd So lor i -• Screes is s ~ • Total Sample plus 10 BBS'll - ICS pi as £0 sasia - 20 plus 40 m&h •-40 5Bsh 15 grass Quarts 2.92ga, l.OOgnj. Other l.lSga. 2.?7g?n» g^OOga, > uu&ris — 44.5A quartz lotss ~ &B ter Kg,it is felt that considerable confidence m y he jslaeei It*. this tet&raiimtlca. ( P L A T E f / r / J / M ¥ £ K O / / G G / T A N / T E AT tf/Gtfiy h/EA THEftEO wi/mv 171: .vlicroscopic Examination . Texture i-file original igneous texture has beenentiroly obliterated in this sample .leaving a muss of highly Uscnifcic s&terial containing angul-ar &M embayed quartz grains.It is noticeable.however.that the groondxrass, ,J although highly stained,is of a distinctly crystalline nature,very little ;| amorphous raaterial being noted. I - ^ineralogical Description t-i CD Quartz - appears as angular and corroded grains surrounded by a nignly liiaonitic satrix.fhere has bean undoubted solution of quarts,the evidence being afforded by not only corroded and angular fragments,but by their consistently aoaller size than in the fresh rocfc.and the fact that in places,grains of similar optical orientation,are separated by the secondary eon^lex. |2| Felspar - several small fragrants of unaltered orthoclase were .i; noted in this section. . • . . . ' . . .. • (3) Secondary Complex -l K general staining is too heavy to allow of any sdneralogical determinations being In the faintly crystalline satrls.fhe absence of any truly amorphous ;aateriul la notable however.In spots where the cotaplex appears relatively free of lisaonite .however .the grourwL-aass is seen to consist of a o&ss of tiny flaay crystals,of rather variable nat-we.fhe following properties wsre detorsinofi for one fc^ps of Ktasral hare present* ' ' Form - minute fls&y crystals ;~'olor- colorless Cleavage- indefinite mica-lite cleavage.parallel to elongation. F L A T E N ° / / 4 /rj &OA/G /TO/VG C/TAN/ TE PLATE /V°/4-M/cutr W£Arrt£f?ED C/TOSJ£P N/COLS X34-P L A T E N ° H 5 G (ft § 4 <2 f/po/titpraff / //jU-rfrof//7g frof/77enfs of Jo/77e Csys/a/ ?s£>ts/7ef/T7t7sj-. J/770//f/ec7tp of HONG KONG GffAN/TE PLATE N°/S tf/GHLr WBATtfEfTEP C/?OJ5ED tf/COL$ X34-172: C-leavagg - mica-like .rather uncertain^parallel to elongation. Twinning - a-few individuals exhibit tMnalng. Birefringence - yellows and yellow reds of first order B.eTractive index - higher than Can.Saisaa Extinction - inclined,tip to 20 dag. Orientation- crystals ore length-slow Tim above properties would Indicate gibbsite.The form in which this mineral occurs here however is different fro® that in which it appears In &2,bei»g raore flaky and less tabular.Sibbsite is distinguished from daolinite,which is also present,by its higher birefringence and Inclined extinction* . i t is believed that both kaolinite and hydroaica are found associated with the'gibbsite in these unstained spots.It is Interesting to cote that one large cry»tal,at least,of feolinito does occurfsea photograph).This relatively large flaky crystal was positively identified as kaolinite, with seas hydromlca intergroma with it along cleavage planes. Iron stain ia ubiquitous,except for these previously asntioned spots fhore the groundnass can be distinguished.It occurs as an amorphous stain^and safely i© named liTaonite.'fhers does se&m to be a tendency for' tbas-a^Jrotja iron ©xl4e to 'be pvg&e&t as a finely crystalline material in a fev? places though,acd this crystalline phase ssi? undoubtedly be cal-led gothite, . . Hal ley site, in one place #srhera identified exhibited a very lov; indef*-inite hirefringence- and rnrked shatter cracks.She quantity of this miner-al present is impossible to estimte under the aicroscope. -A little chloritic material found,resultant upon the alteration of PLATE NV6 c/-ys/a/ o/ A>yc//-o/7?/ca /b/e/yz-o ir/7 rer/h/cu/as c/-jss/b/s <?//r<70//>?//e 228 /JOWG/fO/VG GffAN/TE H/C//L r h/£ATf/£/T£p Crtosssa /v/cou srs 173: biotite.waieh was not observed te-tfcie. sas^le,sithough it ^ e& by son© of the nearly colorless Mcs-ilise aatortatl-'present. • lefflartes-A number of photographs are inc laded. Plate 12 (plain l i g h t s 60} gives so:® idos of fete texture and the manor in which iron-staining occurs, Plate 13( crossed nicols.s 34] illustrates the crystalline nature of the ' mtris and the solution and replaoaont of quarts v,hich has occurred.Plate 14 C crossed nicolo.x 34) shows an unaltered fragtassfe of orthoclase,and fragesnta of quarts,separated by the gi-ouudaasa,originally part of one crystal.Plato 15( crossed nicols.x 360} illustrates a crystal of fcao Unite . j , " • 174' Jc) Cneaical imagination fhe chemical analysis of this material is as follows: ! sio 2 67.74^ -•'i! 19.74$ - 2.46/b •1 Fee ! t IgO 0.09/i OaO f i sa 20 % 0 i h2g- Q.m% 0C2 O.O&JI ?i0 2 • 0.ssj5 ) 1:; She above analysis was taads in the Hoc ice feller Institute for Bocic i • Analysis at fXaeoasis. isKr ' Hi: ••• AlgOg / BlOg 0.29 'II KgO plus JSa20 / AI2C3 — o.qz% ' r' . < : I'i 1 ' OaO /AlgOg- --0.00-••• »iiMEalq£ic Calculation i! In general the ss>sa procedure •was followod in calculating the ainer-i alogic content here as for k2.The following- results were obtained: Ii . Quarts 44. Orthoclase d.48^ s Sericite 2.34^' Ii':: I • • • Chlorite ;)•! • Ilnaaite I'I t Magnetite Q .06& 1 witaoaite !l! 'ii « Dihydrate frilydrste 10.77^ Both the dihydraie and trihydratc as shows above are silicates and correspond to fcaollnlte. and halloysite,The above calculation balancos cor-rectly .but makes no allomnce for gibbsite.One of two possibilities are open; either gibbsite was incorrectly reported under the aicroscopa,-which is not 175: impossible by aay sean* Ib n * * of e*tr*s®Xy i * t a « * i t e or the secondary c o n d o r t M t s o ® .at io S S t ,of the fethydrate I s the fern of gibbsite .h ica case tl» e x t e n t have to * fcitf*, than that detoralaed.fa view o*. t t o ' f w t gibbsite appears to occur in a M that under the aiorwaop. I t ^ l M y to preset to s o ® , eztent in the latter optioa is the- Uteiy.-.....BeaarHa (II Sample IS represents a highly w a t e r e d pttise of tit® Song J&sag Gcanite »as evidenced by the destruction of original testur©#soiutl0C of quarts^dc-TOloprssat of characteristic secondary tos&r&m silicates set ox-ides .and the heavy staining by lignite*. (2) Whether gibbsite appears in this tssterial appears to be equivoc-al. Kaol inifce.halloysite and hydroaicathov:ever,v«ere definitely proved to oe present. 176: Sample & 4 Texture - loose.porous.earthy,all original texture obliterated. Color - light reddish-brown Screen Analysis Total Sample - 15 gms. plus 10 mesh. -10 plus 20 aesh -20 plus 40 mesh ~ 40 mesh Quarts 1.71gm. 1.0 gm. 1.0 gm.: Other O.gOgffle 3»09gm. 2.86 gm, 2 .64 -gm fatal % Quartz — Uii/o 177: Microscopic Examination (texture ' The origins! texture of this specimen has been entirely destroy-ed.i'he thin-section shows a number of quartz grains of varying sizes in a crystalline,but indefinite,highly limonltic groundless. Mineralogical L-oscription -is&artz, - Quarts occurs as irregular,corroded and angular frag-ments in all siaes from tiny grains.almost too small to be discernible even under the microscope,to fairly large masses.comparable to the grain size of the original granite.These grains exhibit,in places,an extremely peculiar appearance between crossed nicols.the effect being mottled and almost fibrous in places.The regular change in birefringence toward the margins may be ex-plained ,of co'urse, by bevelling due to grinding.There is often,as ^ell ,an apparent coating of the quartz by some secondary mineral. ..Sroundaass - the groundoass comprises a highly stained complex, composed ,for the most part, of flaky.often well-cleaved.crystals of kaolin-i fce .and other indistinguishable minerals„the whole covered by an ubiquitous nantlo of limonite.She limonitic stain in this ease is more yellowish in color than it was in the case of sample 3 . In general little can be done.in the way of determining the mineral-ogic content of this sample by microscopic examination in view of the obfuscat-ing aantle of hydrous iron oxide. jPMTE 0 V 7 7~e*Zaf <fa/77/6/e /r<Z gro//?s are y/j/6/p //? //7a/e/~-/o/'Ze r^/T^/eA' M0/YG /fO/YG G/TAN/TE Pi^rs /v/7 r W£ATtf£/7£0 C/?0S3£0 ATCOLS Che mica I Kxatainat 1 on 175: •The chemical analysis of tills material is as follows: SiOg 66.01% a 1 2 ° 3 21.21% 2 * 11% FeO 0.57% Hg0 0.05% CaO Sa 20 . none K 2 0 0.85% HPO 7.55^ 1.24% 0.08% Ti0 2 0.10% She above analysis \?&s made in tho Rockefeller Institute for Eoclc f Analysis ..Wisconsin* I V .  , ,'• • •  • ; . • - . • . . ' - ' . ' •  • . I : . - ~ I. • . ; Mneralogical Calculation • r j In the case of this sample a determination of the percent of i soluble Al^Cu was made?as 7,ell as the percent of soluble iron.These ware j••'••••'•'/•'• ••'••' : • \ found to be 20.57% and"all soluble" respectively, j The following asineral proportions wore calculated : Quartz 40.9% Ilaenite .15% Carbonates .20% Ziirremite « p •) M Sericite 1« '/a Zeolites 2.68% DiHydrate 60.38% I .-. = ' • • :• .'.'.••. . . • . , . - ... • S Since only 6 asols of insoluble AlgG s ^ere found to be present \ these went to form sericite .An excess of % 0 remained which was calculated I' as a potassium zeolite.In actuality such a mineral has never been reported : to the writers knowledge and it is not expected that it occurs here.The I '• V • • . ; solution to the excess K^O undoubtedly rests with the power of kaolinite and other hydrous aluminium silicates to adsorb the alicalis.If this were / P L A T E N r m f/70 Zb<?rc?j£>/7 ///vjfs-oZS/pep oftpt/ar/Z <?/-<?//7S we// snor/ree/. T/?e c/-yj-/c?////?e /7<?ft//-tf of /fte //st?£>/?//& HONG /fO/VG GRA/V/TE PIA TE /Y°/8 H/G//LK i¥EA TH£REP C/70SSBD N/COLS X S O A * 175: the case there would he no mineralogical Indication of the Z20.There is one interesting point in this connection and that is the apparent power for kaolinite to be increasingly stained as its proportion of adsorbed alfcalis rise3.This subject is discussed by MacGarthy* in a paper on "Iron Stained Sanaa and Clays". Jour.3eol. .?>XXIV.Ijo*4.i925tp.3SP. In a purely conjectural way it is suggested that the uniform staining of kaolinite as evidenced by tills sample nay be due in part to the adsorb-ed potassium. • The generally crystalline nature of the background justifies the cal-culation of the excess alumina and silica as a definite hydrate,the dihyd-rate in this case.From both the microscopic examination and calculation it would appear that the assumption that this material is kaolinite would be justified.On the other hand it was found to be entirely soluble when boiled with 14 1 . HgS04 for an hour.Sither kaolinite,which Is generally conceded to be only soluble in concentrated HgS0 4 ,is soluble under these conditions,or a new mineral with the formula and,in general,the crystal properties of kaolinite,is present.The sane conditions undoubtedly hold for sample K 3 as well. With the facilities at hand an attempt to defin-itely settle this question is impossible. Remarks • • • • • • • ' • . Sample K4 exhibits a lighter colour than K2 although containing a higher liraonitic content.This is likely explicable by the fact that it is more highly hydrated than the latter. feathering here has apparently resulted in the fornation of hydrous aluminium silicate .with little if any hydrous oxide resulting. 177: Sample V 29 lexture - s0ft,rather compact,containing holes filled,in some cases with white crystalline mterial . ( see illustration) Color - dull red,with white crystalline material in cavities. So screen analysis was attempted in the case of this sample as there was very little material availaMe.H07.ever, an attempt was mde to estimate,under the microscope,the quartz content of this roc*.Cm the whole quartz occurs as fairly large graias which m y he easily aeasured.Thls type W a S e s t i r a a t e d comprise about 50^ of the rock v 0 lume ,au^nted by consider-able fine corroded grains of microscopic siee.An exact determination is imp-ossible under the microscope and the above figure represents only the rough-est of approxlmtions. The above photograph gives an excellent idea of the texture of this material in the hand specimen. />/i>aj-er a/ ftVfc » 242 /so/ye / r o N G G/fA/v/ra PL4TE /V°/3 H/G//L r h/EA TV Eft SO C/70SSEP A//COLS X34-1/ 23 178: (b) Microscopic gxagtinafclon felam In general this suable, ta thin-sect ion,is seen to be composed of a number of large rounded quartz grains,nith rather corroded margins set'in a bacagro-und of amorphous material containing- nracerous minute flafcy and fib-rous crystals,as well as considerable quarts in the fora of tiny grains.In caaey cases a zone of secondary minerals surround the l a r ^ qtarta grains.The characteristic red color is doe to a coating of hydrous iron oxide trhich is associated apparently with thu asaorphous fraction of the material.In places concentrations of unstained fibrous and flaky crystals are notable.Shese lik-ely correspond to t m crystal-lined holes so noticeable in the hand speoiaen. - l ^ i ^ L ^ i S r i ^ t i o s SBSSS. - appears as large crystals showing active evidence of sol-ution. This quarts is evidently original and retains9in places,oharacteristic I er&olEs and strain shadows.fhe s l U e s do not represent a true proportion of j • t h i a coarse ga ined quartz .considerably ®oro being present in the original ! sacple. j ^ T m Sroandrsass contains a notable &scust of uicroscopic quartz grain > a.which sight possibly represent secondary depoKitiocsbut lively are ssrely ! original quartz %?hich has bScn cowainttted by Tceathsrlnsr action. • 1 ' ' 'I a places a coating of secondary aluminous crystals are found •j about tbs imrgitts of the larger crystals ( see pboto§rapb}. • ; -JsaasiBKftfi. , i: • • : • . . • • • . • • ' .••••• - • | following minerals vssre observed in the ground sags of this .1 • " : . - i • . . •" ' ' •J I : • • • ' . ' • • • . . ! • •' •.:-,. :" '•••..••'••' - . ' • • • • . . . •' • • M M 6 / f O / V G G / T A / V / T E /V° <5 O &/C//L r W E A THE/TEP C/fOJJED M/r&cs X & O 179 • . ' m m r & l A ~ .next to quarts is the isoat abundant crystalline aiinaral in ' the section.Occurs disseminated throaga the groundsass in the for* of ttef fiascos,and in concentrations,often associated ratter closely with a&neral Sphere it is found as.larger flakes and curved fibrous cryst-als® • Ole&v&go - usually good,Eica-like. i5irefringencs » slightly below that of quartz Bofraciive Index - slightly above tf8a.3al. Extinction- appro*. parallel. Orientation - direction of cleavage is length-slow fhe above properties determine this stineral as Melinite , liasral 9 - wwolly found closely associated with K&olinite.and is places ' acteaUy intcrgro'TO -.?Lth it.Has the 3ase properties as Kaolin!to except that it exhibits & notably higher birofrlnyencealthough this property is sosBabat variable.This aineral- bears a slose r&semhl&me to so-called 'aerieite' ,but since % 0 was found to be abssat by aaaly3is?,lt xaost be tm "a&on-im Ssaoiis ©incrai« of loss aad Sqxt . j : erred to m hydropic* in tadepresont paper* So salneral «&s present W i o a could be definitely raleite* to c-ithsr gibbsite or filaspore^oth of these isLnerais exhibit M r s fringe ace colors of upper ttrat oMcr to tapper U i s d or&sr.l'hs only miners! present -ehich sight even approach these colors is tag aforeaaa.tlonel mineral 3 or hydroaica, and ewes- i f is Iw^Svea cbeaM the colors ba high enoagfi for gibfr-3lte(upper first order colors) ,t-io h^iroraica shows parallel extinction while gibbaite an extinction inclined up to SI degrees, fhem is,howevere * mineral vtoteh appears as rattier tabular crystals is •one or te?o places.lt exhibits upper .first order colors between crossed alcols,ellg&tiy above those of hydrofflic&.of which it resembles a basal r i A T £ / r a \ ^/foAptps-a/?/? stew/'/?/? O / - / h a jt>&c/r t?/~0 /s&s/of Of?*/ S>/770A/t>S7£>6>J w PLATE /-/owe /TO/VG G/7AA// TE #/GVL.rk/EA THE/fMP CROSSED A//COLS xao V29 180: socUoa.f&e' fsot^coever, that its colors are higher imim* . of l a m r , as as s suggest ion of a uaiaiial figare.obtaiaed Mtii the oil-Uaasrsion lans,**®* to distinguish it from hydreatioa* this ffliasml.in v i & s o i V m f a o t t?2at u ^ very iihi^rtant part of the section, was not d e t a i n e d .eiren should this bo possible.trhieh Is doubtful. %droas iron oxide la preeent,as la a considerable , faa»tity of amorphous material.la a fs* places sow of the latter appeared to .shos a very low b i r e f r i n g e n c e w o a l - 5 au^gest tiw preseuce of halloysite, following photographs i-ra iaclu-ied: Plate IS -low p o w (c^oasod »laol&»a. Ml-general testuro of a jsora crystallise part of the scciion Plate IS - lot? po-v©r loro3sod,cicoIs,sC{4} - texture of mr& char-acteristic part of section,also shews ieialiait© coating ob a large quarts grain. i Plate 23 - high poser - (oro'seed *5icols,s 380} .-crystals of inI to and hydroalca. flats 21 - iatoraodiate power -(crossed aleels,* 80) - eftgreg&fclo&d of jaolinits crystals in general grountatsa.-1 f I 181: io) C he ales 1 Ea.ainatir.n An analysis <?f this sassple ia as. fellows -Sl&g 6£.66g ( 2l*?4i soluble Al^Cg | insoluble 4 .24# £>.£3$ Ignition - - cone .•She above analysis ^ d e by the Eockofelior Institat® for Sock Analysis »Wiscos®i»» 411 the 710Z ess in asoluble forar&a «®ll. / S i % ~~ 0 .54 S & t e B l a M ^ ^ ^ a e r j a c i g l ^ content.. The follovlns; proportions estisated under tna Rticroscoiw: amorphous material crystallise a&terial — B0$~40$ proportion of quarts — S0JS-proportion .of ^oftl-forced teo-Unite - -above e'stlrsatione are by necessity rough ant oaly serve as an aid ia at tootles to calculate th« content of aLnerlaa* As shewn above,a determination of soluble a1 £ 0 $ w a mie .but since !M» procedure to bell t * f^torialuia U su % S * 4 for one iumr.thsr* is .a coa-etion as to the Absolute validity of tim result applied to miner-alogical calctaation.'ih® astsal procedure in this case la to use HOI in which' case the ^ divided up as foUowaf soluble - halloysi to ^ allophane^ and cliachite; insoluble - fe.oIinite,bHbbsiteyend d4aspor«,ae as seric-ite and felspar. Scow**- 45© th gibbsite est "Saolinit© are soluble In concen-trated H2S04,and to «hat extent ia more dilute acid is not imora.in sons 0 f t h s Previous samples it does appear that Sao Unite say be somewhat salable 182 - • • m d e r t h Q S e conditloos.aowsver.in lieu of sore definite Information this. • question -mast te left open at present, F e 2°S m s s©»bitie<i with an equal molecolafc proportion of to give i 4.SSJ§ linjocite.By the color of the hydrous iron oxide present in this asm-j *** c h a B c e s ^ fchat represents too high a degree of hydraUon.but for the sale© of simplicity in calculation the proportion of one to one was ••.. chosen*. If! : . ; U 0 £ was calculated as ratlle{ 0.53^}.Fro® the faot»ho«ever,that it proved soluble it must occur &b some unknown form,litely as colloidal titan-:n • • • • • :t! ic acid. J: • • Assuming that the insoluble itlgOg is in the fora of kaolinite,2.06^ 1 o f m i B ateemi were found to be pre sent. if "tool ini te»ia to include both J the observed tooliatta and hydrcaica.thls figure seess loss. M ij  S i ^ s i t e and daispor appear to be absent,both froa microscopic es&sa-i ination and chemical determination {soluble aluaiea) ,the m%$ of the alumina | a n d p a t e r in form of amorphous material.either as hydrous alurnin-| inn silicates,hydrous aloainiaa oxides,or a colloidal trdxiure of alanina and I i silica with adsorbed vj&ter. - • j Trots, its appearance and the comparison ofraits chsruical Analysis «lth ij ? tfaaieof a nuaber of typical laterites and bauxites,this astasle uould he izn-i lately Sg classed as- a Siliceous laterite.If this classification bs cor-rect the remainder of the aluaioa and «ater should bo combined to forza cli- ; acftite,the silica being allotted to free qnartiJ.Bhea this is done oliachite forms 29.26% of the s a m p l e t h quarts comprising about 62%.In general it h a s keen found that alumina and water are present in laterites or bauxites in the ratio of 1 part of alutoina ta £ parts of water.Since this is the ii. f"y.' .11.' ' ' ' " ' 183 .. case i2i- tiis present oaopie it j>h-- ,cii U O . the r e a s o n s ^ ipio^a Here Is appro xisuU-ly correct,at lasust.Since a ] i t r « , i a C C * i U u > 0 ^ ^ H e observe aader the aioroscopo 1,- of ti*» mineral allowed to be preset , ' f i R a l result is below: Qaarta- 62gf •( -OliaoMte 29% Xaailnite gf •Halloysite Mi&DUite i^rf ! Butile 1 ' & 0 atteapt m s giads to e i w giV€i ° 2 £ i 0 t Percentages,since both halloysite M c l i & c h i t e sota^bat variable formlae. Mmmm. •rm mterial represented by sample T S 6 e a s to be a siliceous and llraoaite r this fce , « r n o m i ^ o a fro* , Oc,«™relr.l ^ c t . t * f o l . lowing factors present tfaeogelvest ( M SwOTai of - a t l e M t 20* of tte GO* co^M 6 e the finer quarts eoaW u , eliminated.If at all, ^ a r a < i 8 * 1,1 g B M r a l " * » * * * coaatXtreats « . necessary to a l B t o r l t 8 -0 e f 0 r 8 u * a s ^ ^ ? ^ ^ ^ be 10 s p p r M i a 3 t 8 l ? O U M M * t 0 be „ ^ a t ^ t l j . t f K r a w s 8 , ^ ^ ^ " C l n U y 8 0 , 1 3 8 0 , 1 8 » » « l t « i o s toe fining a»i troaUag of ore on t!,o spot.this « t e r U i is to i spare to te considered oomoroiaU*. •7: 184: ^ s M f a o t a l l , 0 r tfco crot.ru observed lu the- t i w , 5 of ? was of e prisma naiara^Kd the enter!si w «>• - , , * ~ i — ( ru;: sample Is gHdoubtealy priesry tjj ori^ets. 185: Sample J4i A Sexture - all traces of original texture gone.Sample consists of a soft,rataer porous.craably mass of icaolin-iite material. Oolor - wnite to creat^y-^iii te. Screen Analysis - a screen analysis was attempted but no quartz was observed.lt is possible ,t>y gentle crushing ,to put nearly all of it turou^a tne - 100 aesn screen. The above photograpa illustrates the texturetor rathar.lae* of text-ore exhibited by this saaple.Compare »ith the ptiotograxih of sample 541 3 . o/J?/y) o/ yey/^/e^/or/roocrys/o/j //? oa> wo'yS/rovsAoc/rfs.wsra'. /SONG torn GRANITE C/?OSS£P M/CGLS t 3*/A gjr !' i I i! 186 Ibj gloroacppir TftctliHt tetsra -» « , t u b - « , « » 01 t u . , , . . r „ n , s t e o M e d a K I ,at leesfe(of s 1 W e . I a 8 r 6 u o t o r s e l y e r y a t a U t l K ^ ^ ^ ^ -SaaiaiasiaaUJaaaUjiiiaa Saaiialis. - f o r » u » w s t c o ^ p i o ® * , , i a g X a ^ ^ l n tlja s l U e ^ , * r „ 8 t part ta W a I m I t r f o r a l „ s e l J _ u U f o l I E d ^ . . e , ^ , , l 0 r o r n p i a t y ^ ^ ^ " l t ! l « ° o d ^ - I t m o laamge . iaw piatograpsj It l ^ u n g t f t a t ^ m ^ ^ ^ sojfeom this p i " c » ' A l t e r e d ortaooio,, are netloeabl,. w a x « * » . , raBM<,d o f ^ a r . t a t o* tte Kfheie tta & ottar = 1 ^ 3 w r e a o t o d . ^ p t t B l m s D s p l C B o a i - I I , too « U to ! * » « * . „ • , t a 9 r a l s s a o S . a 3 • ••asaomafes*.. SOe section I . p r a « l c i a 1 ? % ^ ^ ^ ^ ^ & ^ plaees tt. ainorp&oaa a s t r a l S h 0 « ^ ^ M r a f r l a s C T O e . HMloy.ite » u l d Iterates appear to bB presem. PLATEN023 /foo/s,?,/? rryj-Za/s /h <?/? o/Tjo/ft/o^j 3 * / A //0/YG /fO/m 6/fA/Y/TE M/C//L y IVEA THE/TED C/TOSSED tf/COLS X S S O 3 * / A 187 . ••:• An .analysis of this s&iapia is ca follows; SIC^ 43„69)f-33.S8& • ago 0.22$ . -ftaO • • fioae •  Sag© 0 .065 • 4 .04^ ie.63/" . . r m a b o v ® aealysi© was in the Boekaffcller nwtUutu for Boele Asal-ysisj^iseoasiii, / — o.en SgO pi«s S*a20 / AIgCs — Q.1S It is intoreBtijfjg to note -the elfaosl; ooaslet-e reaovsl of iron this aafcerlai.tfith the retention of a relatively largs proportion of to© allsalis.She abseaae of-CaO while; aom SgOressaln® Is also soiKrafcat usttsml.. ^Cttl|\tl.on_.of fiiineraio^lo Content.. For fcfse purposes of calculation se say consider all the $10 to be eoafctwxl aoa&aot la the fors of qtjarta.1 solubility detenflnattoB show-eel that 29*00$ o'f.tte OS.Sbg- -altastoa in this aaa^lo t?&a sol able 14 IT H 2 £ 0 4 a f t o r toiling with it for one hmir.fha sioroecope disclosed the pres-ence of -a conspicuous- emvnt of teo lis it©, lit tie if any aoriclte.and a saall proportion of unaltered orthociasa.as svelt as fcae feet that at least 50£ of the sample is aasorpixou3 or nearly so. Assuming fast all ths insoluble aluaina is divided b&teoen kaolinite aafi orthoclase.the latter forsing a r&ry saall proportion of the section I E^T-*  188: the following amounts v.era estimated: Isaolinite-I2.00?;,orthoclase -0 .13& the large amounts of and Sa20 present in this sample m y be accoun-ted for in oao of Urn v.<ays: the first is by assuming that they are present in the fora of seolltesf natrollte-0 .3852 zeolite- I717£&,the second is that, they carried in an' adsorbed state by the largo amxmt of colloidal a&ttar present,as well as associated with the teollnlte.In the first case there would bo undoubted microscopic evidence of as largo an assount as 17% of & zeolite present,should such a mineral exist.A detailed sdorosoopic examination of thin-sections of this sample failed to disclose the presence of any minerals which might correspond to cither of the aforementioned zeo-lites.On the other hand it Is a well Knows fact that the alfc&lla are freq-uently adsorbed In considerable quantity by colloidal sutter in slays and s o i l s m i l as- by teolinite.to a limited degree.Held in thls.aanner there •would he ho ailneraloglcal evMecco of their presenoe.lt is consequently felt that there I s no justification for assuming that potass luia and sodiua are present in definite minerals,and that they do occur associated .miulywl$hthe amorphous fraction of the sample in m adsorbed condition. Iron coabined with an so/aai tsolecular proportion of rater to form 0«S9$ liraonlte.UgO went to forts 0,40% chlorite. Si0 2 ,a| 20 s ,ana Hg0 remoln to he disposed of.Since no other crystalling compounds isere observed In sufficient quantity to be considered in this cal-culation* the rcost 'reasonable solution wo old bo to group the allcalis ,Si0 2 , A l2 ° 3 »a n d H 2 c u n d e r t h e iwad. allophane,which is here considered to be a col-loidal mixture of alumlna,sllica,and indefinite amounts of adsorbed water and alfealis. . 189 She final result of a calculation of the minaralogie content of this sample is as follows* Kaolinite 12.0)? Orfthoclase . 13^. Limonite Chlorite' 1 .40% Allophane 87.00% - • . « From the above mineralogical content,as calculated,there seems to be a higher proportion of amorphous material than is suggested by microscopic examiration.lt is possible that,as suggested before,the determination of soluble alumina is at fault,and that a considerably higher percentage of kaolinite is present.which under the conditions imposed upon it by the det-ermination,proved partially soluble.Halloysite,exhibiting its usual semi-crystalline form,is undoubtedly a constituent,but in what quantity it is impossible to say.Then again,quarts may occur in a microgranular form,too small to be identified as such,yet contributing to the general crystallin-ity of the mass. Suffice it to say that sample 341 A represents a material of either a residual or secondary nature,resultant upon the processes of weathering, v&ose dominant constituents are hydrous aluminium silicates.and from the presence of condiderable kaolinite.which might well be termed a kaolin. 1 190: Sample 341 S Texture Although closely related to the textureiess material represent-ed by sample 341 A both in occurrence and In appearance,341 3 retains soan of the original texture of the parent roe*.It is a soft.friable asterial in which remnants of the original ferro-^gnesian minerals remain.marKed by brown spots and shreds of unaltered biotlte. Golpr Predominantly white to creaky white.containing a number of dark specks. The above picture gives an idea of the texture of sample 341B.C0mpare with photograph of 341 A. PLATE N°24 7~e*fc/-e> of 34/0 H O N G H O / V G G R A N I T E PLATE AT*£4-///emr W£XT//Eff£0 C/TOSSED /V/COL J XJ+ i 34/S . ' 191 • • • ••• lb) Microscopic Examination Texture Under the microscope this material appears a s a finely crystal-line aggregate,in which amorphous material is distinctly subordinate.In places patches of a sericitic mineral occur which are often stained to a deep brown by amorphous hydrous iron oxide. Mineral Description There is a notable similarity between the minerals in this sect-ion and those resultant upon weathering of felspars in K 2. The sane finely granular background is present,composed for the most part of tiny tabular crystals,v;ith no visible cleavage extinction parallel to the length,low bi-refringence, refractive index above Canada 3alsam,andlength-slov; orientation. There is a much highereproportion of amorphous material present ,however,and more well-formed Melinite flakes showing normal cleavage.Gibbsite appears to be absent as r^ll.This finely tabular mineral is likely a form of teolin-ite as apart from lack of distinct cleavage its properties are those of kao-Units . Quartern small corroded grains,occurs in minor quantities in this sam-ple. • . • . • • • " • Kaolinite appears in a fev: places as large vermicular crystals .somewhat similar to those in 341 A. Whether true sericite is a constituent is unknown but appears likely.Hydromica is present showing its usual tendency to grade into kaolinite. Sample 341 3 differs from 341 A in thin- section by a higher crystalline content,a lo^er proportion of vermicular kaolinite crystals,and a much high-er percentage of sericitic iaaterial.lt also exhibits spots in which staining PLATE fZy<r//-o/?7/ca 5* /T00///?/-/£> /JO/YG/fO/YG G/fA/Y/TE C/TOJSeO A//C01.S X 6 O 192 by hydrous Iron oxide.although limited in extentSis pronounced.Where this occurs there is always considerable micaceous material to be found in the vicinity*it is felt that thesesspots represent the sites of original bio-tite crystals. Bernards Photographs are included to illustrate the general texture of this sample as well as the occurrence of kaolinite and 'sericite' . 1 193: i!1 (o) Chemical Examination An analysis of this material showed the following constituents: SiOg , 40 • 47/c A1 20 3 41.30/C ; Iron oxides .22% •y s • Mgo •.. — • Ka20 . ——i— • • . •* 48yC H20 16.22%-TI02 The above analysis was made in the Rockefeller Institute for Soclc Analysis,Wisconsin. • A1 20 3 / SiOg — 1.24 z 2 0 / AlgOg — .01 The most notable feature in the above analysis is the complete ab-.: i;i • sence of titania. < Mineralogic Calculation In Calculating the mineral constituents of 341 S,potassium was attributed to sericite,since no evidence of felspars was observed under the microscope.Sericite was so estimated to constitute 3 .98^ of the rock si; • mass. Bo estimation &£ soluble alumina is available for this sample and consequently it is with some difficulty that a calculation of alumina 1 b e undertaken.However the following points are of interest.First that no crystalline quartz is visible,and second that little or no amorphous material is present.These points would seem to indicate that silica is in a combined crystalline form.An examination of the section microscopically indicates that the larger part of the slide is composed of the sans miner-al.With these facts in mind,all the silica was combined with alumina and ! water to give 83.08$ kaolinite. J I • , 194, • After allowing sufficient "water to satisfy the iron present in the formation of limonite,it is found that just three times as much water aa alumina re mains.These constituents are combined to give the trihydrate gibbsite in the amount of 10.61/S. A summary of the results of the calculation are given below. Sericite 5,98% ICaolinite 82.08^ Gibbsite 10.61^ Jiiiaonite • .25$ It is interesting to note that the similarity between this material and the weathered felspars of £ 2 was px&ated out when describing ths mic-roscopic features of this sample.The similarity is further supported by a comparison of the mineralogic calculations. Sample 3413 represents a fairly pure residual kaolin,in which the major constituent is icaolinite. i i ill - -L 195: _Samples , 430 and 4.29 These samples were taken from a wave-cut terrace of Hong Kong granite.So analyses v;ere made,ind thin-sections failed to disclose anything of particular value or interest. ..Sample B 430; This rock is a rather coarse-grained phase of the Hong ilong granite. The general structure is intact,but the felspar has gone over to a white ,rather compact,substance still r e f i n i n g the original form of the mineral from which it originated. A thin-section of the secondary product reveals a material made up largely of rather indefinite,fibrous crystals,likely kaolinite,*ith some •sericite' and a little amorphous material. • Sample 3 4P.9 This sample has undergone more severe alteration than the previous one,resulting in the production of a less compact rock,in which the rather large quart, grains a*and out in relief against a background of white pow-dery material. This white powdery substance.observed under the microscope,is seen to be substantially the same as 3 430. Prom the appearance of the quart* grains there would appear to be a suggestion that sons solution of quarts had occurred. Sample B 429 o: 1.9.7 General Suamury and Conelus t nnR 1. •Summary'" M g h t samples of Hong Kong Granite v.-ere available- for study, iQ • - fresh, rocir • K2 - partly altered K3 - highly altered K4 - highly altered 729- bansite-like material S41A - textureless kaolin 341B - kaolin retaining texture ! " q ? i t e altered sample from *ave-cut terrace. o 430 - less " » « „ „ !t _ajGeneral Characteristies Textures5' ••'•'• K1 - holocrystalllne,hy£idiomorphic,equigranular. f 2 fine .angular ,gravel-line . - loose,earthy,porous.original texture pone. £ 4 - loose.earthy,porous,original texture gone. V 2 9 ~ consolidated,containing holes filled with white crystalline coating. 341A - soft,compact,chalky .original texture gone. I r ° 4 t r T Z t , C h a l f y ' S ° : S e e V i d 6 D C Q ° f ^xture . Itll - as for l74\T r t Z g r a i n S i n S O f t **olin-llto background. o-iou as for d429 but more compact. Golor: • i£l - light pinkisn grey &Z -cream to buff KS — reddish-brown £4 - yellowish brown ¥29 - dull red 341A.- whi te 341B - white containing brora specks 34S0 - white,sosewhat stained by iron 3429 - " «t n „ Screen Analyses: « « « . i» j s r ^ ^ r s r 8 r e t e t i o n « — * ° f 1 0 — b.aicroseopic Sxaraination J i f i o c r y s t a l l i n e shypidi 0mor phic -roc£ predominantly quartz and fels-c o m f r i s e Predominantly orthoclase shoeing microoegmatitic inter-gro^ths of quarts,and nicrocline with microperthitic intergrowths of albite. oiotite only conspicuous dark minerals little oligoelase is present. 198: £2- texture unchanged-in places felspar practically unaltered,!* others completely fathered to a complex of secondary minerals.Biotite ^ / s t U l be recognized although much bleached.Very little limonitic stain. K3- original texture obliterated -very little amorphous material present. l l f t l l T T ° f ? ?? U l a r 311(1 ^ a ins in a highly l i n ^ U c but largely crystalline groundnass. c r y i t ; n L ? f S o S L T s . S ° E e ~ q ; d a r t 2 S r a i m i n a ^ y . J l l l r Z l ^ 1 1t 6 X t U r e f n e ~ S Q C t i o c e z P o s e s ^ r o u s quarts grains in a background,largely amorphous but containing segregations of kaolinite crys-341A - minute shredded and flaky minerals in an amorphous backgrourd.Little or no quartz,but one or two fragasnts of unaltered orthoclase o b S r ^ t 3413 - finely crystalline aggregate.amorphous material subordinate. c_._ ..Che mic al ISxaiainat i on K1 K2 SiOg 72.37% 72.39% AlgOg 12.85% 15.19% FQ205 Q.5'6% 1.07% FeO 2 » o 7fn 1. 62% SgO 0.26% .03% GaO 1.15/b lagd 2. 26% .07% 5»12/o 4,29% H<>Q 0.35% 'k.cAyo co2 ** - — , . 15/i etc. 9 9 . 6 9 % 99.82% ?.s ineralogical calculations Quartz Orthoclase Albite Anorthite Diopside Hypersthene Hmenite Sericite Chlorite kaolinite Halloysite K1 S I . 0 4 $ 2 9 . 5 7 / 1 2 7 . 5 6 ^ 5.26% 4.02% • • 47/a 7, f 1% K 3 6 7 . 7 4 / 1 19.74^ 2.45% .79% .09% K2 AQ.0% 25.0% .5% .30% 1.6% 0.45% 2.94^ o.si;f 34.77% 10.77% K4 66.01% 21. 21/J 2.11$ • 57$ .05% V29 62.55% 22.57% 4.20, .43% .8 5% '.58% 7.55% 9 . 7 1 $ .05% .26% a 53/1) .90% 99.77% 9 9 . 6 0 ^ S 4 1 A 4 - 9 . 6 9 >> 35.66% .m% PP<Z .Q&fo 4.04% 1 0 . 6 3 / 5 3 4 1 B 40.47JC 4 1 . 3 0 & . 23A 16.22% K3 44. 5% 0 .46f 9 9 . 9 4 > S 100.23% m 40.9% ¥29 62/J S41A 0.13% 341B 0 . 1 5 £ 1 ,-59^ 50.38?i ? 2.0>5 1 . 0,0 .40$ 12.0% ? S.98% 83.06% ? 199 Alloph&ne 67*0/1 Gllachite - i U ' ° Gibbsite — - 7 .7^ — - — : : : r l n gg^-j Z Z ] ; ! ? ^ carbonates ,25% '.08% — — hydromioa — — ? . ? ? ? 9 fee above table is not intended to be strictly accurate,or to give an exact representation of the mineral constituents in the various samples, That is obviously impossible v/ith the limited apparatus available.In may of the above results.microscopic examination does not fully corroborate the calculated amounts.The above table does,however,indicate to soas extent the type of minerals present and the trend of weathering. \i jil • • : . ' . i Diagrams Msswm: I /oo p ^irils earf/js J I If j I ' /4/jOJ t -r &/q<pra/77 ///c/sfr o//s7ff rfe/ofSrt? e?d//7j 0/70 Losses c/c/j-//?g Meotfrer//?? of '/Jo/if ffc>n? m > & & ^ s * * * • 5 i u L O . O/opro/v ///is&rrofJvg A&jo/ofe tf cr/nst-Bosses c/or/ng tVeofArr//?ff of ^Honp /fopf <?/-o/7/te Fig-are 5 V - SA >, \ (profit /fe/of/re C. •>? S7//7a/-o/ Ce> -7-We o //0f?j> /fOrtf 'tv/np bo/iyes isf/tve/ifs b • V Figure 4 200: 2. Gone liis ions Samples K2.S3.and ^present l i o n g ^ ^ ^ ^ ^ ^ altered under the aa^s « of conditions apparently.and which differ ^ the degree of a c t i o n t 0 w h i o h ^ ^ ^ ^ ^ ^ ^ Kaolinite and related products are the, najor secondary minerals produced ^ t h o u g h minor e n t i t i e s glbbsite m y o c c u r ^ e r . appears to considerable solution of quarts during the o f l e s s hydrited than K3,especially v,ith regard to its Uon c o n t e n d s in the case of the weathering products of fct Po granodiorite there appears s o « c e r -tainty as to vrheteer the ^neral occurring so abundantly in all these sab-les and described under the microscope as teoli»ite,is in reality ^olinite or Whether it « y not be a new ^neral th. exposition and o f t t e optica! properties of tooling but possessing the property of being solub-le in dilute sulphuric aeid.lt is felt.however,that so little is really Xnca, about the solubility of *aolinite f r o an experimental point of that.until » r e definite information is a.ailable.or until all the solubility tests on the foresoing samples have been rerun .using hydrochloric aoM in-stead of sulphuric .the question aust be left open. •Sa»le T29 see® to be a true siliceous bauxite .produced under a diff-erent set of conditions than those .crt - - -,-v,„ » , -^ ^ < * c l W tne previous samples. 041 A and 3413 are extremely interesting,If misleading spec-n i®sns.!Biey are closely associated both inappearance and occurrence.From its texture and the fact that it is w closely associated with the unfathered . „ 341B roc, tne i^adiate conclusion is that it/is an intermediate stage between the original rock and 341A ,bich overlies U . i h e analySi3,however,is so.s-V7hat m i S l e a d i n s i n t M t 3 4 1 - i s to contain a relatively high percen-201: age of alkalis .which in 341 3, the less altered specd^n.are almost neg-ligible.Ehe explanation almost undoubtedly rests with the fact that the former sample is considerably higher in amorphous material of a colloid-al nature.this material possessing the property of adsorbing 4b*alis l n considerable amount.lt is interesting to note that the conditions under which these specimens were forasd must have been extremely favorable to the removal of iron and titania.as little iron and no titanium are indicat-ad by analyses.Soth of these elements are usually considered to be among the most resistant to removal during the process of weathering under nor-mal conditions,especially the latter,whicU is often used'as a basis for recalculation of analyses to show absolute changes in c o n s t i t u e n t s . ^ this is not always the case ,hoover, has been shown by Palmer* in his work on Hawaiian soils.where he has shown that titanium is removed at the expense of both alumina and iron.As the field relationships are not known - Soil Forming Processes m the Hawaiian IsIand"ri^ir'Science,X>LXl,Apr. " — — 1 9 3 I . - p . 2 5 6 - P a . l m x r ~ it is impossible to add much to that which has been said with regard to these specimens.There does appear to be a great resemblance.however,bet-ween 341 A and 3 and the material described from the so-called lithomargic zone of many later!tic- deposits. in general the trend has been towards the production of hydrous alum-inous silicates as opposed to hydrous aluminium oxides,and in this respect all the samples with the exception of ¥29 and possibly 341A and 341B are the products of normal weathering processes.729 represents a particular case in which the processes of alteration might well be termed "tropical". 202: Solution of quartz, is everywhere vrell evidenced and nowhere *as there any indication that any of the materials represented by the samples studied .ere other than secondary residual deposits as opposed to transported depos-its. amy other minor points might be commented upon,hut as these are either mentioned in the test of the chapter or Illustrated by the inclosed diagrams, they will not- be repeated, here. Is - „ » • r i I -v 'v \ , t O * &-«•»•>' • « i ll)< \ f , i \ > f JL, f/ I -I S-AT. n o M p M j j j f f l ? • £ o • I - -Volume Three TEE WSAKIBRBD RQGKS OF HQKft gnWfi John Moss Otunmlagfi A THESIS Presented in partial fulfillment o f t he He quire men t s for the Degree of . MASTER OF APPLliiD BULiKCi in GEOLOQ-ICAL BKSIE3SSRIK3-April 1935 K SmMJUL^A ;! Classification, | Microscopic Nasalisation £03 i OUotaical Ssaaiuation * 204 'i " 205 !i ^ i f f i J U ;j Sofiami-lfeseri^ioB :! Sic^oscopic Ssamitmiioii .111111**** ' " 2 0 7 i! Cheaacal Sx&minatioo - so? Saaolfl ^ S-oBoral description • Microscopic Saaiaination ; 211 ; o&etaisal Ssasjinaticn m • • • » » • » . » . . . . . * 213 : l»Stsaanary i ^»Coaolt^io»s . . . . . „ „ , » " 815 <* 217 Sasroiaviii a? q . , Olassificafcioa „ Ohaalcsl Sxastatioo 219 gaapla yirt fe - General Description „ wiorosoopio itaains tion l? J * ; Gfcenical SaaajlnaUoa # SacDl* vi n * feaeroi Description . . . . . . . . . . . . . . . . Hicroscopic Examination „ f f f Chemical Examination • w JSRtpaarT and Cooclgfilftn* - ' -i.Saasary • :Sf s.oonciasiQns . . * Classifications , . t . , „ ^ Microscopic £-xa;aination , * ' ^ Sheaical Examination « £ e •Saaipie TK fl tleneral description « Microscopic ixaoination »» Chemical .Examination . . . . .page 238 .Sample G- 2 .Microscopic .Examination . . . . . Chemical Examination . . . . . . . . . ^ * " « " " • « « • ,, « 244 Sample S 1 Chemical Examination. . . . . . . * » 245 _3umsary &nd Conel-ar; i cm a 1. Stannary 2.Conclusion s . . . " 247 a a m & J a f i a i ^ J B a a ^ ^ Harbour trm^ ,- . , Sample 543A Chemical Examination . . . uwnou o . 250 Sample 3433 Chemical Examination.. . . . . « 252 Sample ggo 'Eteneral Desert o t i o " . . . . . moroscoplc a n 4 Ohemisal W « a t l « II11T1111TTilITI « S Samples 321A&B General Descriation , „ , •> •Oaemicaj. Lamination . . . . . : « Sgamjary .and Concltiairinw 1.Summary 2.Conclusions . . i » . . „ « * « 261 QB&S^Mi BlgiS -r General Conclusions l.-toyai and Addition of S l m t s . , S.Jscompositxon of Minerals - £67" Secondary kinerale * 269 4.«enaral Remarks... . « 2 7 2 AHaana.x , Preparation of 2hin Sections of Friable Material . . . . . . . " 2 7 4 Photographic .Methods « 278 -oOo-;ft Mdissmimm. Chaptax .give Plate 26,(Crossed Klcolo(x 34) V* • % ..ps^e 204-80S Plate 3 , (Uroosed fcieola,£S4> f»*t«>» . . . . . . . « Plate 26,?I£I 0 , EiooU.*X 601 2 " t a r * " — ... » 211-12 mate U9 # ? iU c (Grossed Stools^ &60? , 3 h o s t > o f ^ S i t B - 218-215 Pittt® 30,7X11 29 C,(Grossed Kieols.X £60) S e c o n d a r y B i o t i t e and £ pi d o to •< &IS-BU SMmsLM&s. mat© Sl .VI I I £9 £,(Grossed Sicols.x M ) texture — , « 2S1-222 flat© as ,TUX 29 F , ( G r o s s e d S t o o l s , m i S e z t u r e . « •feEtasJI&gfia M a t e 33»88»:(8*obM!& Siools,* 54} ^ , « £38-239 a s s a SfcsaBtarJta.. • Changes in certain ratios through weathering.,. . , » B16-21? Fxgare- 2.~Helativ.e ebaagee, Ik eonstitoants,* , . , . , 216-21? Figure 3 . Absolute changese!® cowstifcuents » £16-£l? Figaro 4-» Cterdgeo te e©E$titsisi?fc 'ainersls » 2X6-217 Chafer Sly figure 1 . Changes ttt&cartaiB J i & t i o a . . . . . * » £so Figure S. Relative charge in constitaenia. . . . . . . w 250-251 ' Figure-5. Alisolat© changes lu coastitu&jats . . . . . . « PIgaro 4 . S t e i n s in. af serologic contents - 230-231 S t e f e r J g X S Figure 1 . Changes in certain Ratios. . . " a m Figure 2 , B e l a t i v © change s in c o n s t i t u e n t s . . . . . . . « 248-249 Figure 3.Absolute changes in constituents... « £48-249 | J • . Figaro 4 . -satBsr&Iosic caajigaa' .ptgeM&r&U* QBAgffim rrgR i l f f l m g B R . .DIM 203: Lagprophyre Dike •.jSample 71II 29k a.Classification ffhe norm calculation for the fresh rock represented by sample H I I 29k is as followss • Quarts '••••• • • Orthoclase 20.57% Alblte " ' 14.15J& • Anorthite Z2.Q0% Serpentine 16 .655 Diopside 14 .65^ Ga orthosil. 1.55% Olivine i, IlcBuite 1.90% ixagnetite Z.48% Limonite .53^ ' Pyrite »09$ Galcite She thin-section of this specimen illustrates a rock,consider-ably altered but with the texture preserved,in which the following a i n e r -ale were recognised' Plagioclase- likely oligoclase.comprises about slide Orthoclase - about 20% of slide. Augite- about 30% of slide. Ihis composition corresponds to that of a augite diorite,but the texture is that of a lamprophyre. The rock represented by ? I I I 2Si is an augite lamprophyre. • . 204 • b^gisroscattic. j;yarn!nafcion 1'exture • ® H s sample exhibits a tendency to pmidiomorphism.the pyroxene and plagioelase being well formed for the most part v;ith orthoclase forming a filling a b o u t t h e o t h a p C o , 3 t U u e n t s . A u e i t e ^ e a p e c l a l l y ^ for/aid and tends to reproduce a porphyritic te ,ture .Alteration has prog-ressed to the point where it obscures the original texture to son* e J tent* Mineral Description 2 h G ^ a ^ d a n t « « section are plagioclase,augite and orthoclase in the order named.Quartz Is practically absent from the slide*• • Plagioclase - alteration has progressed to the point that it obscur-es the original character of the plagioclase to a large extent .firming is relatively rare and when observed is rather broad and i r r e g u l a r i s rather poor extinction angles obtained and the fact that the refractive index of this felspar is below that of Canada Balsam would point towards this mineral being oligoclase.fhe n o ^ calculation shows Ab 1 4 An 2 2 ,however, which indicates that some of the Albite must be in the orthoclase or oeiated with l t in some way.The alteration products of the pligioele are*sericite'in small flalces.Prom the birefringence of these(2nd order colors) the 'sericite' would appear to be true mica.possibly paragon!te, A little kaolinite and calcite are also present. Augite - occurs as large .veil formed crystals,as well as smaller less well formed ones.The augite is almost colorless and in places is practically unaltered,while in others it has gone over almost entirelv ass-Lase PLATE A/0'£>6 V///29/? L4A7P/?0PHrHE D/rtE P/TES/J CROSSED ///CO/- S X34-V///29 /J 205: to chlorite,in fibrous aggregates and formless mas l ses and exhibiting ultra-blue between crossed nico^s sprrm^r— i . ucj.o.occonacuy iron ore and limonite-,zoisite, and to soms extent secondary hornblende. Orthoclase - this , l r . „ r a , f o r m 3 . m x N f ^ « ^ t h e ^ S e r a i s t» « » s l i d e , a » h o ^ t „ p l u c s s o h M S . a U a n p t , t ^ ^ Orthoclase is « „ « r e l a b e l , , l t 6 r e d ^ o f t e n ^ ^ ^ • M M U t o * sericite and .aoliMte are sparingly S l o p e d i E places. 10 other essential c „ i . t l t » B t . .ere noted.the osly other -inerals present being accessory apatite iroa ore.as . e l l as secoMarj, l i m i t s . 206: c.CneiaiGal assassination An analysis 0 f this material is as follows? 4.9,4 2% AlpO^ 14,93$ lfe2°5 2 .8 &% PeO 6 . 67$ -%0 . GaO 9*05$ Sag'G 1«71% I£2G • % 0 2.60% MSQ~ • XJE^C • CO', ® W%' TiO2 1 • 02jl •Q «05,t Sao analysis was made by Sr. in the laboratories of the University of British Columbia.. She mineralogical calculation has been in the first part of thi« section and need not be reproduced here. 207: Sample Y H I 29 3 Texture - loose lustpy material.some of the original tex-ture preserved in the lumps. t e x Solor - dark brown, Ko screen analysis of this material was attested in view of the fact that little or no quartz was found to be present in any of t*e slides exam-ined. b.Microscopic Examination . Seature con-T h e o riginal texture is somewhat preserved although grefctly fused by a heavy limonitic coating.Plagioclase.although it has largely gone over to secondary minerals.still exhibits 'ghosts' of lancllar twinning.Aug-ite still remains as snail unaltered fragments surrounded by a secondary zone.Orthoclase is highly altered.Ko quartz was noticed. Mineral Description In general a microscopic examination of this sample proves very unsatisfactory.The whole mass is so confused with limonitic stain that the identification of any of the secondary minerals is nearly impossible. Etae felspars are mueh altered to an indefinite complex of secondary minerals.in which 'sericite' is recognizable as well as a little calcite. kaolinite seems to be present but cannot be definitely determined.'^ whole is usually stained by a light mantle of limonite.Xn places small fragments of unaltered and unstained orthoclase remain. Ihe sites of old augite crystals are, marked by an area of very heavy limonitic stain,as well as small fragments of the unchanged mineral.All var-iations between fresh augite and opaque iron stained areas are exhibited in P'lA TE a^e^/rfc/zo/p of os/p/to/ f&jrfisre <At I//// 2 & B C/T05SED N/COLS XS4-/ I//// 2S 0 - 208 the thin-section.Chi or* te " i -or.tc U a o n U e are formed from the breaking dov/n of the pyroxene. Little else is recognizable in the soction.In general alteration has not been very intense,the only real difference between this sample and 29a being in the s l i ^ t l y greater alteration of all the constituent minerals and ths much higher de-pw-r- n-r i„ s " ^ t ^ e ox htumui^ ho re j>reserjfc. c.Chemical Ezaminatinn An analysis of this material is as follows: S i 0 2 49 .56^ a 1 2 ° S 17 .69$ ' 1.49% ' 4.24% ~&2° 1.72% 4 . 44^ 1 .30% G G 2 H e as thsaj ,10%) 1.21* ••• • • B&© . • ignition loss less HgG .22% She above analysis mde in the Hoctefeller Institute for Hoc* Aaalysis/Wisconsitu • l!he ignition losssin excess of i-jiit- -i^^r-p,,-,-. -b ° a ePOhclenupuu TS'ater,is undoubted-ly due to the presence of some carbonaceous matter. BaO,-Ahich was reported in the analvsi« n* ftt--- ~ , 01 Vili ^ as w i i , is undoubt-edly present in the form of celsian whirh u *».»aicn therefore seem to be similar to orthoclase in its ability to resist decomposition, It is notable that 8 has disappeared,pyrite having broken up to form .limonite m t h the liberation of the suLfur.Both TI0 s and % 0 have been eon-209: centratod during the course of weathering. __giacraloaioaI Oaicnlatinn ' l K T i S W ° f t h e fcCt t h a t t h i s material has not approached equilib-rium the calculation of tte mineralogical content is extremely difficult, and the proportions of minerals actually present may differ considerably from that calculated.The result obtained ,however, at least gives an indic-ation of the processes at work and a relative idea of the quantities present. She first step was to combine Cao and 00 2 to give .10£ calcite.lfe 0 3 was united with an e,ual amount of H £0 to Sive 10,50* limonite.Ii02 com-bined with an equal amount of FeO to give I l m e n i t e [ 2 . . w a s r ioted to orthoclase<26.13$ and lsa20 to albite(14.15£). Since unaltered pyroxene occurs still in some quantity one-quafcter of the % 0 was arbitrarily allotted to this mineral .calculated as diopslde wit excess PeO and an equal amount of A1 2C & added(6.61& .iSscesa OaO went to form 13.62^ anorthite and the remaining alumina to form 7.43<C chlorite. Alumina,si1ica and water re.min.ffhe remaining alumina was alioted to kaolinite {7.23^} leaving a sa&ll excess of water and 7.08% quartz. The final result is expressed below in tabular form: Calcite • 10/r Limonite 10.50% Ilmsnite ^ 2.28$ Orthoclase 26.13% Albite 14.51% Fe Biopside 6.81;? Ohlorite 7 .43$ Anorthite 13.62$ Kaolinite f Quartz 7 *0B% Calcite and limonite are likely approximately correct in the proportion shown above.although from the color the limonite may be more highly hydrated than calculated. 210: would * I 0 2 has been shown by its complete solubility in acid to be present ^ ° t h e r ^ ^ U M * that or titanic or TOta titanic acid.Should this case present here or tae u , cess „ t e P TO be used up,and FeO would be liberated to combine with the pyroxene, She figures for orthoclase and albin- --TP „ lively reasonably eorroct. u U not that » „ of « » a l a l i a are present in the secondary micas « » P « . i M » in an adsorbed state * eoUoidal natter than is s h o n * t h e S e it is impossible to „ « » „ tb. amount so No attempt K as « „ to calculate augite as such in o f i t s c 6 a H g . eable con.pcsition.Although alteration is =uite C a n o e d in this s p e c i e some unaltered pyroxene r e n i n s and the only parpen of calculating this mineral is to emphasis its occurrence.lb* ^ ^ £ g 0 o l l l o r l t e Y/hich was determined in tne section. Anorthite combined rtth albite l a t i « f o r a o f ^ ^ ^ ^ remains and the above ttaxav in , xibor-.xn vj.ev. of tne appearance of the slide and the fairly advanced state of alteraH'vr • «a unction of this pyroxene is undoubtedly too high. Should 1 serxcite' be present in any euaatlty the a ^ t of fcaollnlte must be lo,er than that she,m,unless,which see,B reasonable,so^ of the potassium and sodium are adsorbed. Quarts,although shot* to bo present b, the calculation,was not obser-ved in the tain-section.It is,hoTOv-r und-vi^f-Mi- - + • • * i ^ i u ^ u i j U D a o a j ^ d ^ a constituent of this not-orial in the colloid si form, • 211 • ' Sample VIII 29 0 Sexture - reproduced in part by secondary minerals. Color - Eeddish brown. Screen Analysis - not attempted (b)ainpcsconic Ezaalnatlrm At first glance this slide appears to be actually less weathered than 29 3 ,as it exhibits a rather definite texture not unlike the original. However it is soon apparent that little i f any of the original minerals remain and that this texture is reproduced by secondary minerals.In a few places'ghosts' of the pyroxen^ remains and some of the felspars are indic-ated by the occurrence of masses of tiny flakes of secondary minerals.• One of the more common minerals in the section is quarts.occurring in Places as indefinite masses and in others as crystals,either pseudomor-phic,or prisna.tic.The latter form is somewhat rare and generally exhibits parallel estinction.As the original material,represented by VIII 29 A did not contain quartz in any appreciable quantities,this occurrence is clearly secondary.resultant upon the deposition of sillca( colloidal) liberated by the decomposition of silicates. The most conspicuous mineral in the section occurs as platy and tabular crystals with well developed mica-like cleavage.The observed prop-erties ares' in ^ P o r E T O U ^ e l o p e d in prismatic and tabular forms oections exhibiting no cleavage the form is indefinite. Cleavage- good mica-like cleavage. Color -light yellow-brown. Pleochroism- faint.greatest absorbtion// to cleavage. P14T£N/°£S 7~esfi;/-(? o/o//e/-fc//-c>cA -oA?/ j/Aes />/<??/£>c/<?j<? jfipiV/?- /AO,? y.j i 1 4 / y p f f o p H r F E w m r PL4T£ / v z e W6//irk/£AT//£f?£D c/rojsso ///cois xao / V///29C 212: Refractive index - above Can. Balsam Birefringence - ,033-.035 Biaxial- 2¥ very small Extinction - parallel. V 7 i d e V a r i a t i o n b e f e e e n the birefringence of the basal and other sections is notable* Shis mineral is undoubtedly one of the micas,and since mica is absent from the original material,must be secondary in nature.It „ u U appear to be either a very light colored bictite,or more likely phlogopite. As inclusions .veins,and masses associated v,ith the mica is found a colorless mineral of hiSh relief and high birefringence ( .045),identified as epidote. Another common inclusion in the mica is rutile,in star-like radiating clusters. In many places thavshape of the original felspar crystals is preserved by a complex of fine gained secondary minerals,outlined by I n i t i o *ater-ial.She grain size of this secondary complex precludes the possibility of determining the Constituent minerals. In so® cases 'ghosts' of the old augite crystals are noticeable,the original shape being retained by a heavy Umonitic stain. It is interesting to note that staining is not ubiquitous.neglecting the quartz and mica in favour of the sites of old pyroxenes and the consider-able amount of indefinite material present.In general the original texture is evidenced by iron stain,that is to say,the original minerals were apparent-ly stained about their boundaries early in the process of weathering,and al-though the mineral was subsequently removed,the form remained. PLATE M°£3 / (/•/yosf 'ofc?ts<?/fe ctysfa/ /H/see^ c/r/er/fg m/yp/mFHmEw/m PLATE//*£3 w m w L r t v s A THE/?EP C/fOJSED /V/COIS X360 y/// C i.e.). Chemical Examination 213: The analysis of this sample is as follows: SiOp 48.40$ AXrjOr/ & o 24*81$ 11.09$ PeO .57$ j%g •#46$ OaO .24$ •ffagO- none KZ0 1 < 12/b HoO lo«*17/& hp G" 1.69$ OOP less than . 110., Ignition loss less H 20 .5Z% ! The above analysis was made in tne liocKefeller Institute for Hock ; Analysis,Wisconsin. 11 *.".-•'• " • - . . . . • • . . •••."'. ; 23.48% of the total 24.46$ alumina was found to be soluble in 14 15 H2S04 .A11 the FeC as well as the was soluble. Mineraloglcal Calculation One of the most outstanding features noticed in comparing this analysis with that of saaple 7III 29 3 is the p u * d 6 a b d r e d u c t i o n in the alkalis as vsell ss calcium and smgnosiusi.lt may be safely concluded there-fore that little of the original minerals remain. The ignition loss reported above taay be attributed to carbonaceous material. • 2he fact that all the iron is in a soluble state shows that no comp-ounds of iron are present which are not soluble in sulphuric acid. In general,due mainly to the identification of relatively large quant-ities of a mica of unknown composition,a mlneralogical calculation of this sample is extremaly difficult,and at best can be little better than approx-% imate. ' Crys/o/ efs<?C0/7(/a/-y of e/>/c/c>f<? M/IPftOP/JYffE G W E PL4TB W°30 THE RED CffOSSEP N/COLS XJ60 .'••:• 214 The following procedure was adopted; All the insoluble alnalna was attributed to sericite.Fe„0* was combined with wtter to form limonite.All the titania was attributed to rut lie. Calcium was divided between calcite'and epidote.All the jfeo was allotted to biotite .Excess alumina. went to form kaolinite, the remaining silica forming quarts.These Be s ul t s are shovin belows Sericite . ' 3 . 13$ ' Limonite 12.46ff C&lcite .io% Sutile i .o% Epiaote .87f Biotite 6.45?? Kaolinite 56.Sl^ Quartz - 17.46$-Bpidote,as shown above ,is apparently too low from microscopic o-aain-ation.Ihe same appears to be the case for biotite. Kaoliniteson the other hand,gives little evidence of Its presence •••••.•..• t • under the microscope.especially In the quantity suggested by the calculat-ion.Should it occur .despite negative evidence under the aicroscops.it -would have to be soluble in dilute sulphuric acid,which point,as a&ntiohed before, is doubtful but appears unlikely. In general any attempt to calculate the mineral composition in this case seeraa almost impossible. There is a possibility that the mineral identified as rales,is son© form of hydrous aluminium silicate which has been stained to ths yellow-brown color eshibited.lt is interesting to note that kaolinite adsorbs some dyes readily,and v.-hen stained, is pleoohroic. Something anal ago us m y have occurred here.ffhis is just offered as a remqte possibility is an attempt to explain the apparent discrepancy between the thin-section examination and the analysis. 215 nummary and Conclusions 1. S umtnarv ffexture ~ :ture VIII 23 a - laraDrophyric te: V I K S G " * * f ^ V f S e l y destroyed,loose,earthy v U I u - original texture largely gone.br!ing idary , , gone,being replacea by a somewhat similar but secoj test ure » Lo o se,e ar thy. VIII 29 M - dark grey VIII 29 3 - dark brov.n VIII 29 0 - red brown jglcrosoopto Examination t e * U to obscure original texture - ^ S H U y iesa so.Alteratie quartz noted. . ion " " v * ™ * fragments of augite are present.Ko auaarte ™ted se VIII 29 C -considerable quart;; and secondary ferro-raagnesian mica are present, Sica contains i n c l u s _ _ a n xly stained,Wt unevenly,the old sites of pyroxenes betn ions of epidote and rutile.Whole heav-3 especially marked. SIO A1203 PeE03 FeO % 0 OaO EapO k26 h2o %Q-*io 2 3a0 Ignition los less H«0 .a Chemical £xamlnntlpr VIII 29 A 49.42$ 14.93$ 6.67% 7.55% 1.71a. 3 .43$ 2.60% .ll£ 1.02J® 99» VIII 29 3 49 « 36/b 17. 9.36j£ 1.49% 4.43% 4.80 1.72% 4.44% 3.73% 1.50% less than , 1.21/v .26% " /99197^T 10% VIII 23 0 48.40$ 24.81$ 11.09JS .57jg .45% .24$ none 1.12JP 10»17)C 1.69g less than ,10;C 1.03^ • 53/& looTio^r 216: Kineralogic Oalculati ons Orthoclase Albite Anorthi te Serpentine Bxopsi&e Olivine I.l>Q3nite Magnetite .Lirnoriite Pyrite Calcite Hutile Xao Unite Sericite Biotite Chlorite Boidote VIII 29 20 57/k 14. Ib/o 22.00% 16. 65/« 14«65;i . 3.48/5 « D^ /t' ® 20/1? fill 29 3 7 »0b)a> 26 e /tf 14,51/; 6.61/i lG.SOjfc Vfif 7. 7 .43^ VIII 29 0 .. 17.46$ 12.46/-. • 10'/i) 56.31JI 6.45 % In the case of this a&terial the calculations proved,in general, very u n s a t i s f a c t o r y a p a r t from a few minerals such as l.imonite,and a general Indication of the degree of weathering of felspars etc.,they :are valueless. J?tg*are 1 zoo /?//ro//j CoO ffg/O __ FeO ^ - I w | 0/c'ffra/n •Sfiotv//?? /re/ot/ve • //7 etor/opfrtoMenqp Figure 2 Figure 5 C/7<J/ff<TS Weor/r&r/ttp of Figure 4 217: 2:Conclusions In general the usual processes of weathering are evidenced in this material.Pyroxene breaks down giving rise to secondary material and liberating iron in. the form of llmonite.Felspars give rise to hydrous al-uminium silicates and minor quantities of calcite,sericite resulting in minor quantlties. As usual plagioclase is the first mineral to be affected,with the ferro-magnesian minerals nest,and orthoclase the moat resiatanat. Pyrite,which was present in small quantities in 29 A.bre&fcs down readily,followed by magnetite,in this'case.accounting for some.ateleast.of the limonitic stain which is one of the first indications of alteration. l!his limonitic stain outlines the various crystals and pre serves, in part, the texture of the roolz even in advanced stages of weathering. As alteration progresses the felspars go over to a fine grained complex of secondary hydrous aluminium silicates.forming soafc calcite,and liberating colloidal silica.'i'he pyroxene is altered from the mrgin inward being found in 29 3 as residual fragments of unaltered augite surrounded by a highly stained opaque area preserving the original shape of the crystal. In the case of this material the colloidal silica seems to be redeposlted, in part.at least.within the roci itself.giving rise to secondary quartz.This quartz is usually formless but appears pseudomorphic after primary minerals in sol® cases. That the advanced products of alteration in the case of this rock are rather unusual.however,is evidenced by the occurrence of relatively . large quantities of a mineral identified as a form of biotite in the highly weathered material.Kpidote is also a common,if minor.accorapafaimsnt of the 218: mica .Curious star-ilk, radiating inclusions of rutile in the biotite are conspicuous.Xhat biotite m y result through norml gathering of pyroxene has becfc pointed out by Johannsea'.aad the present instance,although unusual, is therefore not tmprecedentad.lhmie has also been described as a secondary mineral consequent upon the processes of satan© rnhism. Ihe formation of the aboveaentioned minerals gives the highly altered material a deceptive micros*™ ture .apparently less altered,on cju-sory exam-ination, than the. interifisdiate product. The absence of well f o r ^ d Melinite- and sericite crystals i s notable. If these minerals occur,as would seem to be suggested by the calculations," they do so in a very fine-grained asinner. So what degree araorphous catarial is present is impossible of determin-ation in view of the heavy stain. Fro* the foregoing remarks it will be seen that the weathering of this rock results in products quite d i s s i M W fro* any so far do scribed. To what extent this is resultant upon local causes as opposed to the composition of the rock is uncertain. QH&PSSS SIX o m m m fghpsyht DIHE Sample 7III 29 B 2 1 9 Classification She mode calculation of this material is as follov/ss Quarts 28.02% Orthoclase 31a14> Albite 24.63$ Anorthite 6.95% Mopside 4 .75$ Hypersthene .90^ Ilssnite Calcite .10% Allophane 1.10% Limonite 1.60J6 So thin-section of this specimen was available in this case,in view of vlhich the classification must be aside from the mineral calculation and from a consideration of the partially weathered material represented by ¥111 29 S . Prom an examination of ¥111 29 is it is apparent that the original rock possessed a coarsely porphyritic texture,in which phenocrysts of quarts are present up to 1 mm. in diameter.. The rock belongs to Class 2(dark constituents between and b0%) Order 2 { plagioclase between Ab 9 QAn 1 0 and Abgoaneo),Family 6 " {Orthoclase to Plagioclase-1:1 approx.) and might be named a quarts monsonite porphyry or an A&amillifce porphyry. Should the plagioclase prove to be more, basic,allowing more albite to be attributed to the alkali felspars,in the form of microperthitic inter-growth v?ith microcline,as is so well evidenced in the Hong iftmg Granite spec-imens, the rock would be classified as a granite porphyry.As there appears to be sons evidence of this ia ¥111 29 3 , i t is likely that this rock is related to the Hong Kong graniteas a dike'chase. 220 , Chemical Examination Since no thin-section of the original rock was available the only additional information which rnay be included is the chemical analysis of this rocJc. S i O g 71 .06$ A 1 « 0 „ KJ 'A 13-. •-"-4:7/1? Fe20g 1 * 4 7 $ FeO 2 . 6 5 $ % o . 3 6 $ CaO 1 . 4 3 $ l f e 2 0 2 . 9 1 $ £ 2 0 5 o H p O . 5 7 $ H£O~ . 0 8 $ g o 2 . 0 6 $ Si0 2 . 2 9 $ £his analysis was made in the Eockefeller Institute for Rock Anal-• ysis , Wisconsin. The presence of contained water in this rocJc indiaates that even this material is not entirely fresh.PegOg, in excess of that required for normal mineral calculation is another Indication of the same fact.For this reseon 1 .60 $ of linonite was calculated tall being attributed to this t!/ mineral.Soiae water still remains which wass combined with alumina in the ratio 6 :1 to form allonhane. / 221: Sample VIII 29 £ Texture- loose,earthy,original texture preserved in the „a . lumps Color - light reddish brown Ho screen analysis mas attempted in consideration of the porphyritic. texture exhibited by the thin-section. Microscopic Examination Texture-The texture of this rock is porphyritic,relatively large pheno-crysts of quartz and orthoclase occurring in a fine grained mosaic of quarts and felspar. Mineral Description Quartz- occurs as large anhedral phenocrysts as well as compris-ing the major part of the .^roundmass. Phenocrysts- do. not show resorbtion phenomena and show^,for the most part,very even extinction.In one or two cases where wavy extinction was observed fracturing and granulation of the quartz is also present indicating the action of local stresses.iimonite is found coating the boundaries and penetrating crac&s in the phenocrysts. Groundraass quartz- the most conspicuous mineral in the ground-mass.Occurs intimately intergrown with felspar. Felspar - the only felspar identified in this saaple i-as or-thoclase, which is found as large phenocrystsfas well as intimately mixed with quartz in the groundoass. Phenocrysts - large anhedral,rarely subhedral,crystals which are rel-atively fresh in view of the general appearance of this material .Alteration e PL4TE M°'J/ Porfitiyr/f/'c ftrrfi/re of / V /°L4T£ N'J/ •i f G/?4A//r£ FO/fPtfVffr SL/Gt/TLr h/£A TH£/T£0 C£OSS£D N/COIS X s M - 2 2 2 Alteration takes the form of a brownish cloudy effect and a streaky appear-ance between crossed nicols.Limonite has traversed cleavage planes in places® Groundmass Orthoclase- occurs intimately associated with quartz in the mosaic-like groTmdma.ss.This phase is little more altered than that of the phenocrysts. In general a rather interesting micropegmatitic intergrowth in notice-able about the margins of the orthoclase phenocrysts. In no case was any identifiable plagioclase discovered.This is interest*-.-, ing since plagioclase was definitely indicated in the mineralogical calculation However in a few places masses of fine-grained and apparently secondary mineral s are found which may mark the site of old plagioclase crystals. Ferro-magnesian Minerals The only ferro-magneslan mineral which seems to have been originally present is biotite.lt Is found here in a bleached and altered condition,but does not form a particularly prominent constituent of the rock. Biotite occurs as small subhedral crystals,in several cases surrounded by quartz.Alteration has resulted in a lowering of the pleochroism below that normal to biotite.Iron -ore marks cleavage planes,in cases being so abundant as to completely obscure the original mineral.Limonite has been released by weath-ering,and a little chlorite formed. In general it is felt that the thin-sections do not give a truly repres-entative picture of this sample since,of necessity they were made from the more consolidated,and hence less weathered part of the spscinen. Plagioclase has been almost entirely destroyed,while orthoclase is rel-atively fresh. / 223 Chemical i^aniination An analysis of this raaterial is as followss '9 • 72.76$ 15.80$ Fe203 1 .49$ PeO .43$ .05$ Gao ^ 2 ° .11$ 4 .40$. % © ; 4 .29$ • .42$ • Q 0 2 . ' " .10$ -• . 19$ She above analysis was made in the Rockefeller Institute for Hock Anal-ysis .Wisconsin. _JUneralogical Calculation The usual difficulty is found here in calculating the mineral contents eg impartially weathered rock where minerals are still in the process of change.It is impossible,for instance,to assign a composition to the weathered biotite.An attempt was mad© ,however,to at least arrive at an approximate composition,by following the method shown below. T10S was combined with an equal molecular proportion of Feo to give .30$ ilsenite.Fe2G3 was united with an equal quantity of water to form lis-onite.1%0 was attributed to chlorlte.C02 plus an equal amount of WeO gave carbonate. Sa2o has been largely removed in this Material.She la 20 remaining my be either in combination with the orthoclase or in the form of secondary mica. That it is not present in the form of plagioclase is evidenced by the complete aosence of CaO.In this case sodium was attributed to paragonlte,although the foriibr option is just as reasonable. 2 2 4 The remaining FeO was allotted to diopside. Since orthoclase is so little altered in the section,and sericite was not observed,practically all of the Kgo was attributed to orthoclase. Because the microscope affords no clue as to what type of secondary combinations of aluminium,silica and water are present,&l 20 3 ,Si0 2 ,and water were arbitrarily combined as the definite- dihydrates and trihydrates,Sxcess Si0 2 forming quarts® The final result is presented in tabular form below. Ilmenite 0*30% •Limonite 1.60% Carbonate © £~>0/{, Chlorite «22.% Paragon!te 1 . 52/i' Diopside Sericite 1.59 % Orthoclase 25,02%" Dihydrate ZS.S0% 'Irihydrate 1.92/o X^LAHSUP t2l 42.12% The dihydrate may be assumed to be in the form of kaolinite,and tri-hydrate as halloysi te. Should the above assumptions be true only about 5% of tbe alumina in this material is in a soluble form. 2 2 5 Sample VIII 29 F Texture - loose,earhhy Color - light reddish brown F'° 8 C r e e n analysis was attempted for this material. Mcrpscoplo Examination The original texture has been largely obliterated in this sample. The section shows numerous corroded fragments of quartz in a highly stained groundmass.A few'ghosts' of old felspar phenocrysts are marked by a fine-grained,relatively unstained complex of secondary minerals.Sites of old micas are M e d in a few instances by opaque pseudomorphs of iimonite.As a rough estimate about 30$ of the slide seems to be amorphous. Mineral Description ' . '^uar ta Present as grains of varying sizes,emphasizing the original por-phyritic texture of the roc*.Tho quartz shows rather corroded boundaries and appears to have suffered considerable solution.Quartz would comprise 40-50$ of the section. . . . ' Felspars A few tiny fragments of unaltered orthoclase still remain,but apart from these the only evidence of the original occurrence of felspar is in the rare 'ghosts*. In view of the heavy staining the identification of secondary minerals in this slide is extremely difficult.The 'ghosts' of felspars are relatively free of stain.however,and are seen to be composed of amorphous and crystalline /Yefe '<p6osS 'a/ fp/s/ior i v/z/^ss? G/fAN/TF POFFHYffY C/r0S3£# Af/£01S X34-\ 226 material in approximately equal proportion.She crystalline fraction is C o m p r i s e d o f a v e r y ftne,rather flaky mineral with refractive index above Canada*.Balsam and low birefringence { dark grey).Where there is a tendency to crystal form it is seen that the extinction is parallel with the elongation, and this coupled with the fact that a few crystals exhibit a vermicular form would suggest that the mineral is kaolinite.A definite determination of mat-erial as fine-grained as this is impossible however.A few micaceous flakes are present ,as well, which in view of their f o r m , e x t i n c t i o n ^ high birefrin-gence would appear to be sericite.As so® material also occurs with intermed-iate birefringence,hydromica is likely a constituent as well. Bo coarse-grained secondary minerals are present in this rock.In places .however,apparently on the original site of biotite crystals,a coarser fibrous and flaky/of mica-like material is conspicuous. 227 Qhexsical Examination She analysis of this sample is as follows! *sf SiOg 62.16/1 AlgOr, 21« 28/t> Fe2°S 4 .52$ FeO .70$ ago .07$ OaO • HagO .06$ iL,0 1.02/& HgO 8 .09$ H20- 1 .09$ COp .10$ •8 6f i0 2 .36$ This analysis was made in the Bockefeller Institute for Eooic Analysis, Wisconsin.. 19.62> out of the 21.28/i> alumina present was found to be soluble in 14 I!, sulphuric acid.All the iron was soluble .as was the titania. Mineralogical Calculation Limonite.carbonate .and ilmsnite were calculated in the usual manner. Unaltered orthoclase altough identified isbpresent in such small amount as to be negligible .All the insoluble alumina was therefore calculated as sericite. Remaining alumina,»vater.and silica were divided between the dihydrate and trihydrate.excess silica being attributed to quarts. The result of this calculation is given below. .Limonite 6 .19$ Sericite Carbonate .17$ llmenite .61$ Dihydrate 47 .47$ Trihydrate £. 89$ Quartz 37.06$ 0 .72$ of the rock is in the form of free alkalis.not accounted for in the above listing.These are likely held in an adsorbed condition by the amorphous material present. 228 If the &ihydrate is assumsd to be kaolinite as might be suggested by microscopic examination,several difficulties are immediately encountered. In the first place all of the dihydrate is definitely soluble in dilute sulfuric,whereas kaolinite is thought to be insoluble under these conditions. Another point is that the possible 2.89^ of amorphous material allowed by the calculation is far below the amount actually observed under the microscope. Here,as in the case of many previous samples,there does appear to be room for further examination by such means as ^  the X-ray and dehydrat&in tests.especial-ly the former. As has been pointed out before ,titania was found? to be completely soluble and is therefore most likely in the form of hydrated colloidal titania and not ilmenite as calculated. 229 Summary and Conclusions 1.Summary Text-ore - Fill 29 D - holocrystalline,porphyritic. ¥111 29 j£- loose.earthy,texture preserved in lumps. Fill 23 P- loose ,earthy,original texture gone. Color - Fill 29 D- light grey Fill 29 £ - light reddish-brown. Fill 29 F - light reddish-brown Microscopic Examination Fill 29 D - no section available. Fill 29 B - porphyritic texture-large anhedral phenocrysts of quartz and orthoclase in a fine-grained mosaic of quartz and orthoclase.So plagioclase present although'ghosts' of plagao'clase crystals remain. Orthoclase very slightly altered.Biotite occurring in very subordinate amount has been bleached,and the cleavage planes filled with iron ore with the liberation of liraonite and formation of snail amounts of chlor-ite. ....... Fill 29 F - original texture largely gone.Few 'ghosts' of felspars rem-ain as relatively unstained complexes of fine-grained secondary minerals. Several pseudomorphs of limonite after biotite wore noticed.Quarts,as corroded grains of varying size,is the most conspicuous constituent. About 30% of slide estimated to be amorphous.So secondary minerals def-initely determined due to heavy mantle of liraonite and their consistent small size.Mineral thought to be Iraolinite recognized,as well as seric-it/©© Chemical Examination Si0 2 a12.°3 Fe203 FeO MgO CaO KagO k2O h 2 o a^o -0O£ Ti0 2 Mineralogic Calculation Fill 29 D VIII 29 ii Fill 29 F 71.G6J» 72.76% 62.16^ 13.47$ 15.8GJi> 21 • 28 1.47% 1.49^ ^ <9 /& 2.65% • .70% 1.43% .05% .07% . 1 lf'0 . 0 6j& 5.50% A. 40% 1 .G2^> .51%' 4.29% e.09% .08% .42% 1.09% ' .06% .10% . 10/w . 29% «1L <7/ti .36/ti 230 0rthoclsi3s 'M^ite. Anorthite Mopsi&e IlmeM te Oalcite Mjasalte/ . 'Mloj&aa© Sericite .faragofeite m m m s. -'-•aojS : --iuiojS" '..•412 £5 *t2jf 1 BUfl? • 1 1 ^Stefiratst^Irous. a lustolm aillcsteiJ?®; Trihydratei rt " « ) 1 Chlorite .60 ^  .fill 2 f . . .an • M W f . £>/og ro/rt. s, o/rotv//?? cfie/jpes \ • - . • J. ."•"• \ ' CerTd/sr S?of/e9. A c/vr/s?? Weffffrerr/tp \ ' ' ' \ \ Figure 1 Figure 2 Figure 3 t Figure 4 . . 23i • '• ' 2.Conclusions In general the weathering of this rock has been similar to that of both Hong Kong granitetand 3?ai Po Granodiorite.Bothing of particular erest which has not been dealt with before is present. . Undoubted solution ofnquartz has taken place.Another interesting fact,that applies not only to this rock,but to nearly all the types examined, is the fact that in general hydrous aluminium silicates appear to be the al-most exclusive products of the weathering of felspars. Staining appears to disfavor 'ghostsS of felspar phenocrysts.lt is possible that this is due to the apparent tendency of limonite to be deposited on amorphous material rather than crystalline. Here,as for the bulk of the other weathered specimens examined,there appears to be a discrepancy of some sort.between the araunt of soluble alumina ,the calculatedpresence of kaolinite,and in many cases the microscopic identif-ication of the same mineral.According to. the analyst kaolinite is insoluble in HgS0 4 under the conditions imposed upon it by the solubility tests.At the same time the presence of kaolinite would appear to be indicated by mineralogic cal-culations,and there is no doubt that a mineral is present which under the mic-roscope beeeables kaolinite in all determinable characteristics.And yet all of the alumina attributed to the hydrous aluminium silicate { dihydrate) in the case of ¥111 29 F.for instance,is in asoluble condition. As pointed out previously the inadequacy of attempting to examine this type of material by the methods here available is further emphasized by a study of this group of products.lt is suggested that a detailed examination by X-ray and dehydrate ion methods might help to solve the difficulty in this, as vie 11 as the former .mentioned instances. - s i m s mi m smw poaMisx 2 3 2 Sample TK 1 Classification norm calculation of this rock is tabulated below. Quartz 27 .95$ Orthoclase 24 .74$ Albite . 22 .48$ Anorthite 12.54$ Hypers the ne 7 . 12$ Magnetite 1 .75$ Ilmenite .91$ Apatite . 29$ Under the microscope this rocis is seen to consist of large subhed-ral crystals of plagioclase{oligoclase),with less numerous and smaller anhedral phenocrsyts of orthoclase and quartz in a fine-grained mosaic of quarts and orthoclase. By Johannsen's system of classification this rode belongs to Class 2,Order 2,Family 7,and might be termed a porphyritic granodiorite. •Since biotite is the prominent colored mineral this sample would be most fittingly described as a porphyritic biotite granodiorite. . • • 2 3 3 b. fluoroscopic Examination Texture ,... 'f The texture of this rocJc is porphyritic .large subhedral crystals (up to 8mm.by 4mm.) of oligoclase.with smaller anhedral phenocrysts of quartz and orthoclase appearing in a groundmass mosaic.predominantly quartz intergrown with lesser amounts of orthoclase.Biotite is not abun-dant but occurs as relatively large subhedral crystals in a few places. Mineral Description Quartz-Phenocrysts The phenocrysts of quartz are small and rather angular,often exhibiting corroded boundaries.Extinction is for the most part even,there being evidence of stresses having been relieved by fracturing.Inclusions are rare,and when present consist of apat&tite and gas bubbles. Sroimdmass The groundmass is a fine-grained mosaic composed for the most part of small irregular granules of quartz.intimately intergrown with each other and with minor amounts of orthoclase.lt is interesting to note that this phase of the quartz exhibits extremely irregular extinction. Felspars . Plagleelase. Plagioclase occurs as large well formed crystals showing fine lamellar twinning.The approximate composition was determined to be oligoclase of an intermediate character. The most interesting feature of this mineral is the relativ-ely high degree of alteration it has suffered.All the crystals are to son© 2 3 4 extent altered,while in afew cases secondary products are so profuse as to practically obscure the original mineral. . Alteration-The alteration of plagioclase in this rock is somewhat different from that exhibited in the other specimens so far examined.Here for the first tine epidote is a prominent alteration product,varying in color from i- green(pleochroic) to colorless,and found both disseminated through and veining the altered felspar.The mass of the secondary material Is composed of a fine-grained,rather indefinite complex in which secondary mica,a kao-lin like mineral,and calcite predominate. A most interesting end noteworthy feature Is the presence,in several places,of chlorite in conspicuous quantities,intimately associated with the secondary cornplex.it is obvfious that this mineral can not have been directly resultant upon the weathering of the plagioe1ase4but must owe Its presence to the introduction of magnesia,released in all likelihood by •the decomposition of ferro-magnesian minerals in the vicinity. Orthoclase Orthoclase is found most conspicuously as relatively large anhedral crystals,although it forms a minor part of the groxmdmass.lt is very fresh in comparison with plagioclase and biotite,alteration taking the form of a slight cloudiness extending out from cleavage planes.The boundaries of the crystals are slightly corroded. Biotite . The only evidence of ferro-magnesian minerals in this sample are masses of secondary minerals preserving the structure of biotite,a little of which remains intermixed with the other minerals. 2 3 5 These secondary aggregates consist of chlorite.epidote.and iron ore»the original structure of the biotite being preserved in many cases by iron ore along cleavage planes .intercalated with chlorite.epidote occ-urring as rounded grains and veins . iipidote is a fairly common mineral throughout the slide.being present in the groundmass as well.both in disseminated grains and aggregates. Except where it is found as a secondary mineral consequent upon the decomposition of biotite.magnetite is not common in this rock. FL4T£M°J3 rejT/jre of Ta/ A7o s/??/? /^orf/Ayry 771/ m o sz/A/v po/?pur/?y PL4TP WSJ PPPS// CP0JSP0 tf/COlS Ga 236 .Chemical ISxamination The analysis of this sample is given below, 8iG„ 68.84/a AI 2 6 3 .1.6/1? FepOa FeO S.50£ ago 1.00£ CaO ^ • KagO , 2.66% k 2o 4,19% h 2 0 •• • H20- .06% COp . • 1Ifo TlOg .41% This analysis wasxmade by the .Rockefeller Institute for Hock Analy-sis .Wisconsin. Mineraloglc Calculation In view of the fairly highly altered condition of this rock the norm calculation w?s deemed inadequate and a mode calculation was attempted. The following results are only suggestive of the minerals present,and can not hope to represent true proportions. Quarts 29.82% Orthoclase 23»91% Albite 20.36% Anorthite 6*12% Diopside 3.02% Hypersthene 5.62% -tlagnetite Ili&sni te .90% Sericite 4.55% Chlorite 1.00/i? Kaolin » Cliachite 1.36% Limonite 1 « • > C I S ? X.dO/s Calcite .20% pi dote 2.12% The above calculation was made by Dean B<,W„ Brock of the University of British Columbia.It is felt that these results are in general correct except that the amount of limonite given above is obviously too high from 237 microscopic examination.Since biotite possesses a variable composition diopside and hypersthene are calculated instead although neither occur.For this reason it is likely that sons ,at least of the excess iron,nay be att-ributed to biotite instead of liraonite. Remarks Such features as the common occurrence of epidote tt»rdu$hout the slide,as well as the inconspicuous amount of liraonite g ^ a s n ^ in the presence of considerable magnetite,might suggest a certain amount of hydrothermal action in bringing about the alteration here evidenced.To what extent weather-ing has influenced this, rock is unknown but in view of the difference in trend shown hore when compared to the other rocks so far examined it is felt that alteration in this case is more dependent upon the action of isomorphism than it is upon katamorphism. •J 2 3 8 Sample TK 2 Text are - loose,lumpy,origins! textuer partially preserved. Color- reddish-brown. Microscopic Sxamination Texture The examination of the thin-section discloses a material predominantly quartz,which takes the form of large phenocryst s, surrounded by an indefinite altered complex.The original texture,as regards the por-phyritic structure is thus preserved,but is indistinguishable in the groundmss. 'Mineral Description Apart from the fact that some epidote was notea,and a little unaltered orthoclase still appears tG be present,microscopic examination proved useless in the case of this sample. Chemical Examination The analysis of this material is as follows. Si Op 68.49$ Al 2D 3 ^ ^ a FeG 14.97$ .47$ % G . G8$ OaO .55$ SagO ZpO ago 1 .62$ 3.75$ 3.63 a2o~ co? TiSg . 64/4 . f o .49$ This analysis was made in the Rockefeller Institute for Bock Analysis Wisconsin. 2 3 9 Ttle P r e s e n c e o f a l t e r e d orthoclase in this sample indicates that alteration is not complete.An examination of the analysis substantiates '9 -microscopic examfcnationfconsiderable quantities of the alkalis remain and even calcium has not been completely removed.The most outstanding- indicat-ions of Icataraorphism arc the transformation M rrost of the iron to the ferric condition and the addition of considerable water of constitution. Mlneralogic Calculation 8 ,00$ of the sample is in the form of soluble alumina,all the iron and titania being removed as well by the action of dilute sulphuric acid, insoluble alumina was attributed to orthoclase.albite,and sericite,the calculation giving 20.02^,12.58^,and 2.39£ respectivelyof these minerals. Although this distribution appears logical,it Is felt that difficulty would be met with in explaining the occurrence of unaltered albite here,when near-ly all the calcium,in other words the plagioclase,mth which the albite is associated has been removed.There is at the same time insufficient insoluble alumina to satisfy the requirements of paragon!te,should the l?a2G be calculat-ed in this form.In the same way,although a little orthoclase was noted under the microscope,it is a certainty that the amount calculated here is altogether too high.But here again there is insufficient insoluble alumina to increase the amount of sericite over that caiculated.lt is suggested that at least some of the alkali/* is not in combination as silicates but is in a free state and is held in an adsorbed atate by colloidal material and hydrous al-uminium silicates.Should this be the case the reasoning alkali might be recal-culated as sericite and paragonite without exceeding the determined amount of insoluble alumina. Equal molecular proportions of FeO and TiGg are present.These were com-2 4 0 -bined to form i Ignite .This was done more in a spirit of conventionality than through a belief that ilnenita is present.In view of the fact that all the TiOg proved soluble it is more likely that the titanda is present as titanic acid. GaO was divided evenly between diopside,as representative of the unaltered ferromagnesian minerals p r e s e n t e d epidote which is known to occur here in some quantity.Sxcess after diopside was determined was now attributed to chlorite { elinochlore) which wasurs in conspicuous amounts. • Fe0Os was attributed to limonite. Shan the remaining aluminiua and water arc divided between the dihydrato and fcrihydrate and combined with silica,quartz is found to equal 34.2%.When they are taken as oxides quartz amounts to 43.2$. • Although It is impossible to say in which form the alumina is combined,the forasr alternative was chosen here as being more in keeping with the general apparent tendency exhibited by other related weathered rocks. The final result is giton below. Quarts 34 .2$ Orthoclase 20.02$ Albits 12.58$ Sericite 2 .39$ about « 12$ KagO adsorbed Ilmenite »-82/S Galeits * IQyfc-Diopside 1.08/fe Epidote 2 « 0 4/v Chlorite 1 . 50$ Lizsoni to • 4 .53$ Sihydrate{silicate) 16.77$ Trihydrate( " J 2 .76$ Both the dihydrate and trihydrate are soluble,and has been the 2 4 1 CASS in so many of the samples so far examined there appears to be an-other example here of a possibility for a mineral hitherto tmdesoribed* 242 Sample H2 - Microscopic examination Texture The thin-section of this rock shows phenocrysts of quartz.ortho-clase,and plagioclase,with relatively large anhedral biotite crystals,ana smaller altered hornblende crystals,set in a very fine-grained and highly altered ground mass.The quartz,which forms the most conspicuous phenocryst, occurs as rather angular grains ,variable in size,and showing even extinc-tion for the most part.Plagioclase,the next most common phenocryst,is found in subhedral form,again varying widely in size.Orthoclase,not occurring in great quantity,is anuedral in form. Mineral Description Quartz Phenocrysts .varying widely in size.showing,for the most part rounded' boundaries,although in a few places there has been apparent corrosion. Extinction is for the msot part even,there having been considerable relieving of stress by granulation in a few places,and by fracturing in others,with subsequent filling by the groundmass. Plagioclase Plagioclase is found in anhedral to subhedral crystals of variable size.Very definite zoning is noticeable in places,the composition being basic oligoclaso to oligocl&se-andesine.It is interesting to note that several crystals have been fractured.their relative orientations being main-tained, the groundmass flowing in along the fractures.Alteration in some crys-tals is very marked while in others it is almost absent. Alteration .- alteration of the plagioclase takes the form of an indefin-ite complex,often spreading out from cleavage planes,in which secondary mica?. 243 occurring as flaky and fibrous to radiating aggregates of variable biref-ringence.Ko other minerals are definitely determinable.although a little epidote seem3 to be present in close relation to the felspar. Orthoclase Orthoclase is foun§ as relatively large subhedral crystalston the whole remarkably free from alteration.which when it does occur,takes the form of a cloudy material,often densest in ths centre of the crystal. Fe rro -magae s i an Jaine ra 1 s The most conspicuous dark mineral is a dark brown variety of biotite which occurs as large subhedral crystals,showing on basal section,little evid-ence of decomposition.Here again an interesting fracturing with subsequent filling by the groundmass is present.The boundaries of these crystals are sur-rounded by a coating of chlorite. . There appears to be definite evidence of the original existence of augite crystals,which have been subsequently altered to secondary hornblende .chlorite,and iron ore.The main evidence of this mineral is afforded by the preservation of the basal.right angle cleavage,by Iron ore in a number of instances.lt is interesting to note that while biotite is still relatively fresh,augite has entirely disappeared as such,and is replaced by secondary minerals. Epidote,although present,!s not nearly so conspicuous as it was in TK 1,although the groundmass Is ?nore highly altered in the present case. The groundmass itself Is so fine grained and in this slide,so wea-thered,that little can be done with it except to state that quarts,in unknown quantities is a constituent. 2 4 4 Mineralogies Galculation The analysis of this rock is as follows. SiOo 67.55% AloQt C O 14.05JS P e 2 ° s 0.06% FeO tz 1} w MgC . 1 .04 % OaO 3.09/b Ifa^O 3 .36 Kg 0 4 .01% % 0 0.71% HpO- 0.01% COg 0.00% TiOg 0.22/v 2r0n 0»00/S P20g 0.14% C5 W ' jf 0 • li/^ t* MnO The above analysis was made by T.C.Phemister in the laboratories of the University of British Columbia. In material of this type it is nearly impossible to obtain an accurate calculation.For this reason the ordinary norm calculation,given bsicvv,wa.s :. •made. . - ••/.:•-••. .. • .. . Quartz 20 .64^ Orthoclase 23.91/!. Albite 28.82% Anorthite 11 .12^ Mopside 3.35/S . •• Hypersthene 10.65fa . Magnetite . 2 . Ilmenite ..46$ Quarts and orthoclase are likely present in approximately the quant-ities given above.Albite and anorthite.combined in the form of plagioclase, has gone over to a slight extant to secondary products and is therefore present In less qunatity than shown by the calculation.For diopiide and hyp-ersthene must besubstituted biotite and tte secondary products of augite ie. hornblende and chlorite.To what extent kaolinite is oresent is undeterminable. 2 4 5 • Sample 0- 1 Shis material is a redd ish-brown.earthy,loose sample,from which | no satisfactory thin-section was prepared. • • • • • • . . j Chemical Examination •The analysis of this material is as follows. I SiOg a i £ 6 3 Pe203 FeO JIgO : . CaO lago J£gO apo • HgO-C02 TiOg This analyses was made by the Rockefeller Institute for Bock Analyses Wisconsin. Mineralogioal Calculation Ilzrenite.chlorite, sericite,liraonite,calcite,and rutile were calculated in the usual manner. The remaining alumina was distributed between the silicate dihydrate and trihydrate. Sericite tC « C/^J'/i' Chlorite . bl/o Ilmenite 1.06% Rutile . 17/i Limonite 7.51% Calcite .13% ;0g«2Si02.dihydrate61. " trihydrate X • 0 & jfc Quartz 26.28$? When alumina is calculated as the oxide dihydrate and trihydrate. 56.71% .OO/o .49$ • Xb/tf .01% none iaocE' .Wit j® 9.92^ .94^' about.10% . I «5/s> quartz rises to 55,40% As before there seems a distinct possibility that a soluble aluminium 246 silicate dlhvdrate is present. Since TiOg is known to be completely soluble it cannot be -present in the form of ilnenite or rutile,and nay therefore occur as motatifcanio acid in a colloidal form* 2 4 7 Summary and Conclusions 1•Summary TX 1 - porphyritic texture TJ£ 2 - gravel-life " .original texture partially preserved. G 2 - porphyri tic texture S I - earthy.original texture completely destroyed. Color T& 1 - dark greenish-grey T&'Z r red-brown 6 2 - dark grey 1 Q 1 - red-brown Microscopic Examination TX 1 porpoyritlc- large subhedral crystals of plagioclase{oilsoclase) wita smaller anhedral phenccrysts of quartz and orthoclase in Aground-mass aosaxc of quarts and lesser amounts of orthoclase.Biotite Is the ' mos, conspicuous dark mlneral.Plagioclase alters to enidote,secondary mica.possi sly kaolinite.and a little calcite.Biotite alters to chlorite ana iron ore.Suggestion of augite crystals preserved by skeleton of iron ore^ and secondary hornblende.Epidote Is conspicuous through the section as is chlorite.Practically unstained. TK 2 - large quarts phenoerysts in an Indefinite.highly stained ground-mass.i, little unaltered orthoclase is present,and epidote was identified. S 2 - pbenocrysts of quartz,orthoclase,and plagioclase in an extremely ixne-graxnca highly altered groandmss.3iotite and ghosts of av<>ite common.Differs from TIC l ; in that its plagioclase is slightly mre bas-ic, ana shows zoning more definitely- finer grained and more altered 'groundmass,higher percentage of dark minerals.Same general texture and components.iSpidote is also less common here than before. Chemical Examination TK 1 S 1 0 2 6 8 . 8 4 $ 1 4 . 1 8 $ ? e 2 °3 1.21)1 3 . 5 0 $ FeO MgO CaO l.OOJs 2'. 73$ TK 2 6 8 . 4 9 % 14.97$ 4 . 08$ .47$ .68$ .55$ 67.55$ 14.05^ 0.0 6/i 5.82$ 1.04$ Z.09% SI 56.71$ 23.83$ 6 .59$ .49$ ad? >07% E&pO ZgO •nog 248 2 .66$ X 0 4 . 19$ 3 .75$ 4.01> .84$ 3.63/fe e7X/s> .08$ .64$ 0 .01$ . 11 % .00 .47:5 . 49$ 99.79;; 99 .72$ 100.32$ none .29$ .94$ * 10$£ 99.75$ Mineralogical Calculations Quarts Orthoclase Albits Anorthite Hypersthene Slopsids Magnetite II menits Apatite Sericite Calcite Chlorite Liraonite i£j»M© t© Alp0~*2 SiOg.Dihydrate „~ ° <• Trihydrate ivutiie 27 .93$ 24.74$ 22.48^> 12 .54$ 7 .12$ 1.75:: .31% • . 23/o 34.20$ 20.02$ 12.58$ 1.08$ . 92$ 2 .39$ » 10 1 .50$ 4 . 6 3 $ 2 .04$ 16.77$ 20.64$ 23.91$ 28.82$ 10.65$ o .35^? .23$ .46$ £6.28% 1.06$ * 13$ .51$ 7 <?* 61.65£ .17$ Diagrams Figure 1 C/tosrp&s Weaf/rarf/Tp s/fo/? 77/y I L i C J L Y rA/ r/r£ s.£ s/ Flffare Z Cwjf/fA/Fft fj m/ Ab Mam fff Flgars 3 / Figure 4 7' I 2 49 Gonelusions Sample I is the first,so far encountered,in which epidote is a prominent eonstituentat is suggested that most of the alteration eviden-ced in this supposedly fresh material is consequent upon hydrothermal action and not upon weathering. In general £K 1 and 8 2 resemble each other closely.G 2 has apparent-ly undergone soma stress ,llfcely internal .before the solidification, of the groundmass resulting In the fracturing of crystals and receasntation by the groundmass.Zoning of the plagioclase is more marked in G 2 than in TK 1. The alteration products of both are similar.excepth that.epidote is more con-spicuous in the latter,.Both show evidence of having contained augite in some quantity which has been altered to hornblende.chlorite.and iron ore.It is interesting to note the comparative freshness of biotite in the presence of completely altered pyroxene« So thing of particular- interest arises out of the study of the weather-ed samples.In general they exhibit the usual course of decomposition of the various minerals.There has been undoubted solution of quartz during the course of weathering.Jnfortunately the altered naterials are of such a fine grained nature that little can be learned of them under the microscope. In common with a great many of the samples so far studied there appears in both Ttx 2 ana £-1 an excellent chance for an aluminium silicate dihydrate which is soluble in dilute sulphuric acid.This material would therefore merit further study by adequate means. / Oa?2?233 EXiMff B£mhm x y jim m m msmm voLa.-imue ; ; 360 Be-pulse 3a?/ Volca&ftcs Sample 845 A This sample was not at hand,nor were any thin sections found.In lieu of a detailed microscopic description of this particular section,sev-eral other slides including B 106,for which an analysis is available,were examined,the following brief description being a summary of the information obtained. Mainly volcanic sediments,the bedded material being chiefly quartz-ose tuffs.The color of these is greyish to reddish. Texture-porphyritic.consisting of angular and rounded phenocrysts of quarts and felspar in a crypto- to microcrystallino aosaic of quartz and 'felspar.aether interesting absorbtion rings circle many of the quarts pheno-crysts.Felspar is quite highly altered,largely to a complex of secondary white mica. For the sake of comparison the norm calculation of 3106 is given below with its analysis,the microscopic characteristics having been sutsmar-ized above. SiGp 75.37$ Alg0;* 12.17$ Fe 20 3 .20$ Fed 1.78$ .-•• i%G ' .13$ GaO 1.17$ .la20 3 .17$ •&>>0 6.16$ b£© . .34$ fiOg .26$ Ta PoOr . G6/s . S . 18/j • MnO . .06$ The above analysis was made in the laboratories of tiu University of British Columbia by Dr. T .C . Phemistor. 361 jSorm Calculation(3 106 } Quartz 3 2 . 8 1 $ Orthoclase 3 0 . 3 5 $ Albite 26.93$ Anorthite 3 .61$ Diopside 1*25$ Hyps rs thene 1 ,90$ Hagcetite. . 25$ Pyrite .54$.-Apatite , .12$ ... . ..llitofettte' . . 40$ F o r comparison the original norm calculation and analysis for 343 A follow. Analysis 343 A ( Rockefeller Institute for Hock Analysis) Si0 2 75.70$ A1 2 0 , 13.04$ .11$ FeO 1 .30$ ,' . ..'.•.- *2B% OaO .76$ Sa20 • 3 .37$ • . . % 0 4 . 78$ H 2 0 .46$ ' COg .01$ 'no 2 .15$ Korm Calculation . Quartz 34 .02$ Orthoclase 28.36$ Albite 28.30$ Anorthite 3 .89$ Diopside 2 .11$ . Hype r s thene .50$ Xlmsnite .39$ Halloysiirfj 2 .21$ Maohite. . In general there is a close relationship between the two specimens,al-though 343 A is higher in quartz,and the plagioclase is slightly sore acidic. Dark .minerals are likewise present In slightly smaller quantity in 343 A than in 3 106,and the former appears more weathered as evidenced by the presence of more water and a small quantity of GOo. 362 B ( Crust upon 343 A j Hers again only the analysis was available for this sample .and uafor-'9 ' ' • tunately all deductions iirast be based upon this. _.CheaiicaI Examination 66*08% fr 2 19 „40% i'60 0*7 ln09% FeO 1.50% .2 7% ft A « 04^ A <» 14/o ICgO 1.9l£ a2o &»B7/o h2o- ,05% CQr, JM' • U v/v Ti02 « 23/b This analysis was made in the Soclcefeller Institute for Hoclt Analysis, Wisconsin. Hineralogjc Calculation From the fact that plagioclase had been almost entirely decomposed.as evidenced by the analysis,it was assumed that approximately half of the orthoclase had gone over to sericite.11^0 was attributed accordingly. Sinec only enough OaO remains to satisfy the CQg.lfagQ was allotted to paragonite.IImsnite and calcite were calculated as usual. The large amount of ferrous iron still remaining in this specimen sug-gests .since no likely secondary iron compound could be found,that consider-able unaltered ferro-magnesian minerals re main.Hypers thene was accordingly calculated. The remaining alumina .silica .and water were distributed between the aluminium silicate trihydrate and dihydrate,and quartz. This calculation of definite hydrates is unlikely to be mineralogically li I . I 253 II correct, as almost any variation is possible/out represents the only possible method when calculation alone is relied -upon.By this calculation .77 of I '9 ' j the alumina is soluble if the dthydrate exhibits its usual characteristics in these specimens,or if the dihydrate is true kaolinite »7§ trouia be sol-! ' uble® The final calculation is given below. Quartz 39 © U Grthoclase 6® 67/s Sericite &. 7 o'fif Paragoni te 1.61JC Ilmenite .45/i Galcitc- ,07% Chlorite • 51 /L Limonite 1» 2 Hypersthene 2 » 64 JI-" Al203 .2S102 .dihydrate 1.12JC rt trihydrate-Whether hydrous aluminium oxides are present is indeterminable,although it would appear from the amount of quartz,that if they do it is only in very small quantities. 364 Sample. 3 320 •Texture - texfcureless9chalk-like material. Color - whi te ^ * * a i C i ' ° S C O p e t h i S ^ — to consist 0-r avery fine-grain-ad complex,rather homo^eous i* appearance and without apparent structure. A ^ . . n a l l ^ t l ^ corroded quart, grains were seen .gainst this background. Ghosts of original felspar* may still bo c u r v e d as we 11.In .general very •allied by the microscope in the case of this spoc-little information nay be sained l-lK&n, Chemical Examinati nn The analysis of this sample is as follews 73.19$ A l 2 e 3 17.51$ t, S 3 ' " v j FeO .53$ •SfeO - 71 frf G a 0 .05$ 3 .54$ H 2 ° 3 . 98$ H 2 ° " .07$ Of this 5 .25$ of the alumina was insoluble in dilute sulphuric acid. The above analysis was made in the Sockefeller Institute for Eock Anal-ysis,?,'! sconain. Mine r& 1 a si cs.1 Calculation E g 0 was divided between sericite and orthoclase to use up the avail-able insoluble alumina. HgO was calculated as chlorite,and OaO as zoisite. Access was combined with FegOg to form thuringite. •256 Excess alumina,silica and water were divided between ths dihydrate and trihydrate,excess SiOg forming quartz. , The final result is tabulated below. . Quarts • " 5( Or thoc lase 1 a', 34$ Sericite 3 . 04$ Chlorite 1.22% a'oisite .30$ Thorlngite £.13$ A1 2Q 3 .23 i 0 2 .Trihyd. 13*80$ " " Dihyd. 6 .40$ iimonlte .53$ It appears obvious from microscopic examination that the above figure for orthoclase is altogether too high,none being Identified in the slide, As analternative the following calculation is presented. Quarts 52.66$ Zoisite « &Q/b Serici fee - 1 1 . 9 4 $ Chlorite . 1.-22$ Tharingi te 2 . 1 3 $ AlgOg * 2Si0g.dihyd. 1 6 . 5 1 $ 2eolites 9 .06$ Llmonite .53$ Andalusi te K OQ!?f 5i V p This second calculation,by attributing all the insoluble alumina to sericite,a very reasonable assumption in this case,leaves considerable excess KgC ^3 disposed of .Although for the sake of convenience this potassium is attributed to a zeolite it is more likely that it is adsor-bed by colloidal matter or in some other form,as no K zeolite is known. I f zeolite is calculated,there is insufficient water to combine with ex-cess alumina and SiO^V/hich calls for the calculation of andalusite.As andalusite is unlikely in this association excess K would seem to be in an adsorbed form. Although extremely fine-grained the groundless is definitely crystall-ine,which precludes the possibility of allophane,at least in any quantity. if S ^ I | ' 2.5ft 1 As an alternative it is suggested that mostvof the alumina is in the | f o r a o f a fflonohydrated^omica) in which case andalusite is unnecessary. It is possible,in this case tooonfcinu® theorising indefinitely without practical results,and for this, reason this sample is suggested'as being very suitable for further research. Shuringite is calculated. hers,not because it Is felt that it necessar-ily occurs,but because it,or a similar mineral appears necessary to apport-ion the iron.Incidentally ttroringlte itself is described as being rare and resultant upon ;netamorphisa for Its formation. . J3o matter how the calculation is tad© a large excess .of free sjp&rtg | appears inevitable ^Microscopic examination,altfeoug&. showing some quartz , fails to disclose any such quantity as required by calculation.She ans-wer must lie in the presence of considerable colloidal allies. m.• leaky Harbour Voloaoic Saatpla 321 A & 3 Shis spec lawn constats of a grey colored.dense.slightly porphy-ritic roc it. tsith a dar* brown -gathered crust on one edge {321 B)„ Ho section saa available of either the fresh or altered roc is and it Is therefore necessary to depend solely upon choadcal osaffllcatloa' S M M M U s g y M M Analyses C Boclasfeller Institute for 2oelc Analysis) SiCg Pel'Os ?a0 ago CaO la^o % 0 H*0r 64 a SO/fr 15.!?!;{ Z.20% 1.12& 2,15% l.lbjS • 02J-S ,-sof ,q.in&ral1o>:i,cai C&lculatiim, 6b. 5S;C i .79£ .51% •osjs 1.4 SSI A Quarts Orthoclase Albite Paragesite Anorthite Diopside Hypers theno Ilmonite Galclte inllo.vsite Liaonite 21.IS? 25.68a 11.07£ micftr-1«C^A-1« -^O/V-I . oo*; 1.50J? 321 3 Quarts Orthoclase 16.6SX Sericite 5.57% Par&goni to 6.12;;' Slopside 2.00% Chlorite fhuringi to Li:ncni te 6.4 s;S Ilaenite 2.74f& Calcite )a .2SiOg .dibyd .7.29% " mono " 3.35JS,-321 A is. & slightly sosw calculation.SB! B .however,requires soma explanation. Xlaaait© end calcite vera calculated as •aeaai. Since nearly,if not all the plagioolaso has bees, decomposed ,as testi-fied by the analysis,all the Sa 20 *as attributed -to paragonlte .u 2c was arb-itrarily divelded between sericite and orthoclase,the latter mineral being deemed present from the relatively large proportion of %£) y®t remianicg in the material.In the sag® way % 0 mas attributed to both diopsid'.-. and chlorl te.T&uringite ,or 30KB allied mineral,;vaa necessary to use up the •Excess alumina , s i 1 lea, and water «ere divided be tea en the dihydrato, and ooaobydrate ,the regaining silica goifig to form quarts .She calculation of a monooydrate is so£30thing of a departure from the procedure followed previausly.2his appears quite legitimate .however ,froa the findings of Boss and i£crr where they identified the"mica-like kaolin mineral'1 or hy-dromica with a formula similar to kaolinite less one solec-ale of v<&ter. In fact the calculation of a jsonohydstwbe is in reality more reasonable than that of a trihydrate. So solubility tests were mde on this material and it ia therefore impossible to say just what proportion of the alumina is soluble. 369 aummary ana conclusions 'if Texture; 343 A - so speeiraen available M S 3 - ° « * , 320 - texfcm*el6 3S.?ch.&lk~lilJ© material 32IA - porphyritie^dense »volcanic,, rock 32IB - crust on former Color % 343 A & B - no speci;aens 320 - white 321 A - .grey 321 8 - dark brown. Microscopic Examination 343 A & 3 - no slides available 320 - very finely cry stalline s homogeneous irate rial containing a few small corroded quartz crystals and ghosts of felspars. 521 A & 3 - no slides available® Chemical ilxamln-stipn Al 343A i 0 2 75.37$ 2 12*17 "p 3 iuCQ^Q F e 0 1.78/; .13$ CaO 1.17 n r - - . /o o « J. I /e 5.16$ .34$ - i 02 , .26$ 002 343S 320 331A 3213 ^  66.06;t 1 lOi 64.60,;" • 65.53$ 19.40/i 17,51$ 16.91= 12.00$ 1 .09$ . 81$ 1 .44$ 6«32/; 1 o 50$ «53,$. 2 .20$ Bp Sl'/o .27 % . 31 1 . Iltf 1 .79$ .04$ .05$ 3 .15$ .29$ .14$ 4 .02$ .51$ 1 ® 1 3 .54$ ** KClff 3 .69$ 8 .57$ 3.9Q% 1.15$ 3 .68$ o . 80% 1 .47$ .05$ Piftfy .06$ 370 Mineraio<?icax Calculit i on 343 A 3433 320 « Quarts ,34 , 50.04- "!p «j>f »Q Oa,-? S r 28-S65; t'% •fi-lbite 28.30$ 2C. P a r a ^ i t e - f r S ? s Anorthito 3.82$ G a i c i t e .0?$ 10<-Diopside 2 .11$ 2 ^ Chlorite 5 1 < , Hypersthene .50$ 2 .64$ s 49^ " 2 .11$ . 1 $ . 5 0 $ 2.64$ «18% 1L e B/O . IQ.cf . 4 5 $ Thuringite 2 .13$ 3 93*' Liisonite .18  -. ^ 1* 30$ Ilaenlte I ^ f " S S f - ^ f ? Zoisite AlgOg .28i0p .luonohyd " 1.12$ 6.40$ ft cv j . . - _ ... » , « & «/ / tnaya . 2*21J& 39.18?; 13.80$ The above results arc very unsatisfactory and serve to illustrate the total inadequacy of analysis alone in at tempting to examine material of this nature.However»in l ieu of microscopic examination ,and other addition-al infornat ion, i t is regrettable that an attempt at determining the mineral content, by calculation is the only msthod available. Diagrams Figure 1 371 2.Conclusions So little definite information is available in the ease of this suite, that no conclusions of value may be deduced,apart from the chemical changes illustrated on tha accompanying diagrams. . calculation If the alternative analysisffor 320 is accepted,and in most ways it appears the most logical,there might be a possibility that this material is the result of hydrothermal action.However the amount of adsorbed alkali is unknown and it is therefore impossible to say whether andalusite,or a related mineral is present. It appears that this group of products is especially fitted for fur-ther study,not only because of the occurrence of secondary aluminium comp-ounds which might prove interesting,but in an attempt to discover whether a mineral related to thuringite is present. "s CH&P2353 BIKE 0EKbT!A3j COI.OLUS TOES 8 5 4 General. Conclusions In a Kork of this magnitude aany conclusions have,of necessity,been arrived at during- the course of its production.-These sfor the most part, havu been rationed in their rightful places through the test,It would re be next to impossible to attempt a complete/capitulation.but an attempt will be made in this chapter to present a few of the major ideas and observations arising out of the work done on the weathered rocks of the Song Kong suite, 1. .Removal and Addition of Elements During the course of weathering the constituents of a rock: tend them to suffer removal by the decomposing forces acting upon/4*.Although dep-ending, to sorae extent,on the manner in which they are contbinea.snd also upon the direction taken by weathering,in general their susceptiblity to removal is quite regular from any normal igneous rock. Calcium and sodium are the most easily removed,calcium usually going to a greater extent than sodium,although many cases are encountered where the reverse is the case.-magnesium is very susceptible to solution but generally less so than the preceding elements.Potassium,with which Barium may be classed,is the most resistant of this group. Titanium is usually very resistant.but under certain conditions may be removed readily.The same is true for iron.On the whole aluminium appears to be the most resistant of the common rock forrrir:g elcmants. Eot only are constituents removed during the course of weathering but actual additions of foreign elements are made as will.The most notable of these,and one which accompanies decomposition in the earliest stages, is the increase in combined water .consequent upon the process oh hydrat-2 6 5 ion.Another invariable change in the specimens studied is the addition of oxygen,evidenced by an increase in ferric iron and a consequent dec-rease in ferrous i&on as weathering progresses.The third major change of this nature is the addition of OOg,which is common but by no asaans invariable .In this connection caraonation seems to be ,verj- often at least, one of the earlier changes,as shown by the fact taat the OQ-content is often higher in a partly -weathered rocs. than in the corresponding complet-ely decomposed taatwrial. ®he accompanying diagram gives an excellent picture of the relative rates at which the various elements been subtracted or added to the various samples of Hong axing rocks studied.* (Pig. 1} IUxe apparent solubility of the various elements is influenced,not only by their actual rate of removal,but by the extent to which they either forxa, themselves, in soluble secondary compounds with other elements, or are trapped by such compounds * 1'ne direction taken by weathering,and the conseq-uent type of products is likewise important .As an excellent example of these points,samples 341 A & i might be ei-led.341 A,although actually more highly weathered than 341 B,is found ,oy examination of the analyses to contain a higher percentage of botn KgO and SiagO»aad from this alone would seem to be loss decomposed than the other.The reason for this apparent in-congruity,however, 1ies in the much higher colloidal content of 341 A,which holds the excess alkalis in an adsorbed state. Analyses alone are not dependable criteria for the amount of alterat-ion undergone by any particular rock,or group of roeks»the Fe2Cg/ PeO rat-io and the amount of contained water being the most dependable. TiO» acts in an exceedingly variable manner,in certain cases proving 266 " * t * ' m t M y " — U , ~ - d . l t 1 . iEtere jtiEf to jot . « t t „ j p e a r e t 0 b e , r o a g 4 I a r E U e U s a t h e b e h a T i o m Of I n . and M t t » U in thl. ra.pact.lt being n o t a M a that S M * " " H W W W W . te* * » . » removed „ w U . reasonable explanation would -itn o 0 U e ifl fact that the colloidal Iron has .The n©st hydroxides of Ooth these e l e c t s are cloaeIy?,elated in charac . e r . h a v ^ among other properties,ta. same electrical sign.It is therefore that forces tending to remove one would .atvleast affect the other. The rate at which Si02 undergoes removal depends very largely upon the original composition of the rock involved^ quartsose rock,in which quart, and orthoclase predominate.would , 0 f necessity suffer less loss of SiOg,than a basic one containing,for example, plagioclase.pyroxene.aDd ampiiiboie as its essential components.'^ reason for this is obvious when it is'remembered .that quart, and orthoclase are both relatively resistant to weathering,while plag.oclse,pyroxene, and amphihole are quite easily decomposed,Silica is liberated,from such decomposition, in the readily soluble « colloidal form a m may be easily removed. Direct evidence of the retention,or rather deposition of secondary silica,is demonstrated in only one instance studied—the weathering of t lamprophyre dike {VIII 29 A to Ojla all the other samples examined there appears incontrovertible evidence of solution of not only colloidal sili but .of quartz ttself.This question will be discussed more fully in the next section on the decomposition of minerals. he ica / 267 Decomposition of Minerals This subject has been discussed ratter fully in Chapter l,and in general the writer's findings only serve to substantiate the information already given. In general the following order of decomposition of silicates *as maintained,the most easily decomposed minerals being listed firsts plagioclase,pyroxene,and amphibole ( interchangeable order ) orthoclase ,and biotite.There are many local variations ,and for a fuller picture of the subject the reader is referred to diagram 4 in Chapters 3 to 6. In places biotlte Is less resistant than orthoclase,in others more so. In the same m y plagioclase,and the pyroxenes and aaphiboles are inter-changeable .Pyrosene.however,always breaxs down more readily than the corres-ponding amphibole when both are present in the same rock, • I l n E n i t e m & signetite are both quite susceptible to decomposition giving rise to limonite,and in the case ®f the former .colloidal titania. Ihe ubiquitous presence of TiOz in this form in the samples studied was deduced from the fact that treatment by dilute acid in all cases proved all the titania to be soluble. Quarts shov.-ec strong evidence of having suffered solution in all the thin-sections of weathered material examined. Usually the first indication of alteration of orthoclase is the form-ation of an indefinite cloudy material.The occurrence of this stay be con-trolled by cleavage planes,or cracfcs etc. within the felspar,or may be found irregularly scattered at random over the mineral.The latter case is found in one or two instances where the rest of the rocic shows little ind-ication of t?eather^ng.uhere this occurs alteration is apparently consequent 268 hydrothermal action durinS the closine stages of solidification As dec-omposition progresses,small flails and fibres of sericite appear,against a A g r o u n d of tny tabular crystals of a mineral identified as kaolinite. S o - amorphous material is usually present and halloysite is not uncommon. in general plagioclase follows the same line of alteration as ortho-clase, although there seems to be a tendency for the secondary ^oducts to be more micaceous in appearanee.lt is interesting to note that epidote and zoisite,although mentioned by most text-books as common alteration prod-ucts of plagioca4ee observed in only two cases in more than negligible araounts.and the evidence is not conclusive that in these cases they were not consequent upon hydrothermal action. She pyroxenes and amphiboles.and even biotite . begin to show changes at an early atgge.Pyrosene usually reverts to an^hibole.commonly hornblende sonst'ic&s. actinolite.As alteration progresses tha anrphibole.either primary or secondary breaks down with the liberation of iron .either as limonite or iron ere .and the formation of chlorite. Leaching of iron is in reality one of the earliest manifestations of weatherigg.as shown be the preservation of augite and hornblende cleavage .as well as the deposition of limonite on quafctz and felspar boundaries. Biotite first loses color.with attendant lowering of pleochroism. With increased alteration secondary products similar to those resulting from pyroxene and amphibole are formed. In a few instances .epidote in small inconspicuous grains was also noted. 269 Secondary Minerals As mentioned before the common alteration products of the felspars proved to be 'sericite'.kaolinite,amorphous material(allophane) and halloysite.In swfsral specimsns there also appeared to be sops evidence of the occurrence of gibbsite. JixiQ'h doubt has been cast upon the occurrence of true sericite and paragonite as alteration products of felspar by the work of Boss and Zerr. 2?hey point out that the mineral commonly accepted to be secondary mica, proved on several occassions to have the formula Al 20 3 .2Si0 2 .H 20,with only minor and variable amounts of the alkalis5and suggest that this mineral, "muscovite-like kaolin mineral ".belongs to the kaolin family,and may be transformed to true Jaolinite by increased hydration.This mineral,termed hydromica in the present thesis,is characterized by a slightly lower bi-refringence than true sericite but higher than true kaolinite.Judged on the basis of birefringence,the writer observed ,tims and time again,all variations between the high second order colors of secondary mica and the greys of kaolinite.exhibited by the secondary minerals of the sams section,often in close association,sons times even intergrown.The conclus-ion,put forward tentatively by Hies,Lindgren,Soss and Kerr,and other,that an isomorphou3 series is possible between secondary white mica and kaolinite ,in which decreasing potassium,or sodium,and increasing water are the var-iable factors,is therefore substantiated by the present findings. It is interesting to note,as well, that the proportion of sericite, often fairly high in partially weathered material,is lowered while that of kaolinite is increased with progressive weathering. There is little doubt .then, in the writer*s mind that feoUnite may be formed as an end product of a series,passing from felspar to sericite 379 through hydromica to kaolinite.characterised by increased hydration and a leaching out of the alkali, - • . *9 : • . . . . On the other hand this gradational transformation does not appear to be the only manner in which kaolinite m y be formsd.fhis mineral,or one ident-ified as such under the microscope .may be present in the early stages of decomposition as an extremely fine flaky material,in the presence of rel-atively large crystals of sericite.lt is interesting to note that large vermicular crystals were characteristic of only the more weathered material, and that Isaolinite (?) formed in the early stages of weathering was uniform-ly fine-grained. The re would therefore seem to be evidence of the ability of icaolinite to grow in place. Halloysite,often in a faintly anisotropic form,is not uncommon,and the amount of allophane is extremely variable.Just what were the governing factors during the decomposition of a rock tshioh determined the icind and quantity of the different secondary products is at present indeterminable, and ,in fact,results were so variable that no valuable generalizations appeared.Any experimentation along these lines has pointed towards the for mation,of rather release, of colloidal matter upon the hydrolysis of the silicate,the manner in which these substances recombine being depend-ent largely upon the pS value of the solutions involved. In only two instances did epidote appear as a prominent constituent of the samples studied.In TK l , i t is found,not only associated with decompos-ed plagioclsse,btit indiscrimately scattered through the section.There is therefore no definite proof that it is resultant upon the alteration of plagioclase,or even that alteration has been of a katamorphic nature. In fact from the general appearance of the slide,as v;ell as the wide dis-271 tribution of chlorite.absence of limonite.and the aforementioned occurr-ence of e pi dote, the iteration of this rocic might vail be attributable to fcydrothernal, rather than kataaorphic action. The other occurrence of epidote is in VIII 29 C where it is found in intimate association with biotite,both apparently secondary in nature after the decomposition of augite.As a product of weathering.biotite is very un-usual ,and associated with epidote as it is,would suggest dynamic snetamor-phism for its origin,weee it not for the fact that there Is no structural evidence in support of this.On the other hand abundant liraonite is pres-ent,and would support the origin of the H&Mhafeios by kata raorphic process-es. • •• Chlorite is the usual result of alteration of the ferro-magne3ian min-erals in the present specimens.The variety present is commonly clinochlore exhibiting,typically,ultra blue interference color. Liaonite is ubiquitous wherever weathering has affected the rocte in ques-tion. In fact the occurrence of this mineral is one of the fisst indications of deconrpos 11ion.Many cases are found where limonite coats the crystal boundaries and is deposited in cracks and fractures of relatively fresh quartz and felspar crystals.In most cases this coating is the result of the release of iron in the earliest stages of alteration of the ferro- mag-nesian .minerals.In several samples this limonitie stain shows a tendency to crystallization and is therefore in all likelihood the compound goethite. In the present thesis the term liraonite has been used to describe any hydrous oxide of iron,although from the color variation exhibited in the different specimens it is felt that all the so-called hydrates are repres-ented. • • • • • , . I 272 It is interesting to note the variable susceptibility to staining ex-hibited by different minerals.Both felspar and quarts are readily coated ,as are halloysite and allophane.whereas sericite and kaolinite are usually little affected. Secondary quartz was only definitely determined in one case .that of the weathered lamprophyre dike ( VIII 29 0 ) .On the other hand there Is abundant evidence of the solution of quartz in nearly every sample. general Remarks In general the tendency of weathering as exhibited by the Hong- Kong spacimens examined,is towards the production of the hydrous aluminium silicates rather than the hydrous aluminium oxides.With the exception of one sample,V 29 , laterites are absent.weathering following an appar-ently normal 'course. As pointed out on several previous occasions there is doubt as to the validity of the mlneralogic calculations made.To the writer there seems to be such indefiniteness of composition exhibited by the secondary compounds,that the calculations can never hope to reproduce the true min-eralogic content of the various specimens. •71th this in mind ,however,they do retain some value insofar as they indicate broad tendencies.And it is in this connection that there appears to be a possibility of the occurrence ,in many of the specimens examined, of a mineral with the chemical composition.efid Ufeny of the optical proper-ties,of kaolinite.but soluble in dilute sulphuric acid. It is with regard to this hypothetical mineral that the main interest centers in connection with future research on the weathered specimens from Hong &ong9ancL for this reason alone,not to mention others,that scieb-273 tific examination by adequate maans is justifiable. By adequate, .means is meant, the use of the X-ray and dehydration te, ^augmsnted by specific analysis of picked material 9pos:sibly involving-use of heavy solutions and the centrifuge, and detailed microscopic e, inatloa® — OOO" — 'tf • ,/ 2 7 4 reparation, of Tain Sections of Friabla the constituent minerals of a rook can only be studied intelligently uMSr toe potrographic aiorowopa when their thickness has been reduced to a point allowing of the determination of optical charactor,birefringencG, and associated characteristics^ W e a l thia-aoction of rock presents the Meal conditions whereby this say bo accomplished.!^ only this,but it all-' ows of a study of texUral relations ana associations of minerals otherwise impossihie.Fortaaatii^ the preparation of ordinary rook sections is a rel-atively simple natter. 'ihe same observations hold with regard to ths minerals coaprLsin* loose, friable aaterialfaut here the maufactur© of & thin section is considerably store difficult.Eot only must the sateri&i be bound into a coherent mass by so.® cemonting madias/out tftsi cessnting aedium xaust be of a nature,and applied in asmanner not to effect any change in the adneralogic contents. Sinca most material of tais nature is hydrated tc a greater or lesser degree »the latter consideration be difficult to achieve. Host of ths material with which the writer had to deal was of an extrem-ely friable,broken nature,aal considerable experimentation was required befor a satisfactory technique was developed.The following mthoa proved.on the whole,with modifications to salt the sample at hand,the most satisfactory. S?he jaateriai to be treated is placc a in a suitable receptacle (the top of a cocoa osn proved excellent for the par posej and healed very gently over a low baBS&n f l a s s b e i n g t&xan that a temperature of 100° 0.1s not attained.Canada Balsam,prevIously diluted with xylene to ths consistency of heavy treacle,Is now poured on the 3peci.-aen,aoa the heaticg continued for about half an hour,after which the sample is recovod and set asid^ to harden. • • » ..'. ... V • •••" • . • • • . . • • • - ' . . . . . , . . . . . • v . . 2 7 5 Generally a p i s e e the s i . : e o f a haaei nut i s p r o c e s s e d , I f ctre i s t s x e n to iceep tha temperature hole*? 1 0 0 there i s l i t t l e d a n g e r o f *9 de&ydration.Sha continued hoatleg h a s th« e f f e c t o f * o latUl»t»8 xylene p r e v i o u s l y te snaurs a viscosity o f t h e 3anad& B a l s a s concomitant T i t h c o m p l e t e poaetratton,thus allotting the f a s to hardon a a i c » y and satis-f a c t o r i l y , ^ dogew of dilation,mad consequently the asoant o f h e a t i n g i s dependent on t h e p o r o s i t y o f t h e specimen, T h e saturated taaterlal i s a l l o w e d to s t a n d f o r a b o u t S 4 ,tours,at t he e n d o f p e r i o d grinding my be costanoei? .Here again the method f o l l o w etS 2M8t fepanft u p o n the d e g r e e o f hydration o f tie constituents.If t h e r e I s a n y dangsr o f hydration following u p o n contact with water,!t ia b e t t e r t o substitute some neutral rasdlut^sunh ns a mineral o i l ( g u j o l was found e x -c e l l e n t here)in t h e grinding prc-coes.tt might 'te mentioned t h a t the v.-riter found no differences i n any casas experimented upon,between s l i d e s of the saa® imterial p r e p a r e d in b o t h ways,but i n t h i s c a s e the state rial %&s a l r e a d y h y a r s t i i d . \?a»n ' water is need a s a asdiosugrindir.g I s cosnssBced o n the c o a r s e s t e e l lap,us ins S o . 2 4 0 &mery p o w d e r p l a c e s u r f a c e I s produced on the speci rmn a & ! then s-aoolhed u p o n the f i n e s t e e l lap to.303 i.5s>ry.2o farther p o l i s h i n g i s required i f this last s t e p i s c a r e f u l l y perfcrJaed. I n t h e s e a n U m n g l s s s s l i d e h a s b e e n g e n t l y no a ted ai^d & drop of S&n-ada 3cIsan placed upon it . Ilea ting I s costinuad -until a l l the diluent xy-lene h a s b e e n volatilized,usually a oatter of a b o u t 10 p l a n e surface- o f the spocis©n,«iiich h a s been tfeoroosfcly cashed,and gently h e a t -ed, i s nov p r e s s e d firaly o n t o tae b a l s a m on the s l i d e , e n d s a t e~ay to c o o l . Great euro is required T?ita this s t o p lest air bubbles be forssea between 276 the slass and the speoissn.lt is generally sufficient to allow the slide to set for zn hour,but is evont of an incomplete removal of xylene by the previous heating,a longer period is required. Grinding- is now recosssnced upon the other side of the sample,the stops being essentially the s&se as before.lt is usually safe lo cut too chip down to about 1/16 inch ok the coarse lap tesfcre transfering to "SOS". Shore much free qs&rtz is present in a soft background,hc»e?er, aor© o r e is reqaircd to prevent "plucking- out " of the quartz.In this case it is butter tc cossaecco f ina grinding earlier and transfer to a glass plete for the final stagof?tir, rjone eases it bairg wisest to <3o ail grinding on the .gifes plate. • If a-t this stags ifc ts noted that complete saturation of the sample by C Canada Balsas was not achieved in tha first place, tt is often possible by carefully heating the slide s-M adding stsre ftum , to ensure a complete sat-uration. i,s the required thickness is approached, the progress of grinding aast be constantly checked. salcroscoplc ©xaain&tion.If quarts ,for instance, can be doterrsined,Lt proves m excellent guide to thickness.£0 facilitate oaaalmtlos daring this sta^s a drop of «ater la placed -azm tne surface of the ohip.fhe final steps are performed upon a glass plate ttlta So#303 erasry ponder.Care is required to .prevent plucking- or the ro c it slice Is of the ro qui site thicicness the next step is to cover it with & glass", to do this the slide is wasted thoroughly and heated vory gently for just a sufficinet tiro to wars it thoroughly without raiting the Balsas. X drop of s e i U ^ goa is bow placed on the rock slice e®d a warned cover 277 5ia3S proosei firaOy spot, i threat ears Is required Here;first that IrobbllEj; of tho Balsam does not occur disrurstiBj,- tho rocx slice.ar,;? ts 9 that the cover jlass ic secured ic place uitheut c.uy air bubbles being trapped teaeatte it . If care is tawm the slide muy be used alsost irsnediutely ,but , i f poss< Ibie/it should bs set aside- to harden for st least a day. is aontionftd before,t?ith the materials available wo* the type of spec-imens involved,the aothod here outlined prctud very satisfactory.;, number of different s&thodfl have been outlined by various tsorlcerc -sith friable jaaterials.lt la possible that so?» of these weald prove raoro satisfactory the one followed by the writer although m attempt at rev lets is jaad*,the following references might be uasfui to anyone atteaptics (11 ¥s.rm&l of Petroii^iM-io Sotac-is *-£!cGr:s'?.-:in1,1313,pp.599-603 .Johannsen® (2) Microscopic Study of Clay a -U«S.G. fc., Bull. 708 .Append i x. Somrs (3) The Tecjanique of preparing "bin-Sect lens of Sock; - Utah engineering ixper intent Station-Gniv.of Utah,1323 pp.0-18 -aead (4} Preparation of Shin Sections of Friable Ssteriel-Jour.ueci. ,DUv\?X,Is0.6,<\Tt3'-Sept. .192G- Leggate (5) Thin-Section Mineralogy - lie Gravr-3.il I , 1932-,pp. 3-7-i nogsrs and &&rr-(6| Ife tho&s of Pre pars-1 Lor. of tredi.fcentsry listeria! Tor Study-iicon.leol. .vol 2 1 , p p . 4 5 4 1 9 2 6 - Ho S3 , / 278 Photographic Ifathnrt* , A b r i e f r e v i e w o f t l ls Photographic nethods employed might prove val-ua'ble. For all straight-line work Process plates were used .Exposures in the photographic rack were 2 mins. .aperture 22,for S | by 4-J- plates. 5 x 7 plates call for at least 2 | mins. aodak formulae D 34- A and B were used in 1»1 ratio.Shis particular developer is admirably fitted for straight line work as it tends to emphasise dark and light. For microphotography the microscopic eyepiece was retained in all cases not only allowing of & short bellows to be employed but giving a picture better defined about Its margins. Exposures were variable dependent upon the source of ligit.whether or not crossed nicois were used,and the type of material.The best results were obtained by employing a small projection lantern for a light source.'The insertion of a green filter usually resulted in better definition. With this set up,exposures when using crossed nicois.varied between and Zh minutes.In unpolarized light the exposure is 'usually 10 to 30 sec ohds.The light factor of the green filter used was approximately 2 when using Panchromatic plates. For Panchromatic plates D 61 A developer proved the most satisfactory. An acid hardener fixing bath was employed in all cases. Sibllograa^E- giviag fch© various jmblioatioas Is alphabetical ord&r. of author8s .usases* -Auor^ -no-as- icon. Geol. I I , 1907, p. 630 Cim. Seel. 5ar. I I5 , I9 Iy . Xdes-pp.56—, 60-65* 'IsCAerm. Eitth.,szil,13QC,pp.i-Gl ' lote on formation of Saolin minerals froa F«Ispar- Jour. • fleet, vol, xL, ao .0 , Jiov.-Dec. , I33£. fssslta Annual Bept«tJ.S.;}.S.pt.l,X39i- Origin .sm4 B&tts*e of •sells.* U.S.Q.S.Mon.47,1904,Sreat ise on Hetaraorphism. Ashley- Golloia Sfe-ttsr of Slay-asi its leasare-ssssts. 3arrell~ Joar* Seol. xn .no-S, April- i2ay,I9DS,p.29S.- Gllmt© and Sorrest-1»1 Seposit®. 3arto»~ Jour. #eol. «o.24,I*I6.pp.3S£-89S- liofces o® Mstietsgratioe of Granite is jigypt. Jahrbuch. far iiin. , vol. 11,1698,pp. 192-219. fiortfcier-Aon. iDes Uinee, 7ol.vi,lG21,pp.«Sl-&:>4.' .. ^lacisselder SI lot- 5oar* Qeol. Bo.3StppX3*-i«0.~PltfiBg »e' a' seatMriog mg® Jour. geoi. svi,1206»p286- Olimte a M ferrestiai • ©epoeite* Jo*ar. §001. Voi.xxxlii m -Bee .l«25gpi>#Bfc-SS. Exfoliation as a Fhase of Sec* Weathering. ' Boydell- frans. Inst. Kin -and Set. lias. 1924-the role of Colloidal • - j Solutions In the rOrmalion• of .Siasral Beposits. Bracmr.J.a.- Ocol. Soe. of A f r i c a , Bull 7 ima ™ * u 1 * » p p , D e c o m p o s i t i o n of Hocxs in 3rasil„ Buchanan- London, ISO?, Vol. 11, rn.*ss»4<*7 , * * - a Journey fros l!a€r&s through the gantries of Caaara and gala tor. • Burton- ilec. 'ieol. Sur. tola, * l v l l l , p t . 4 . m 7 , p . £ a 4 . ^ ^ £aoii»ifjetion and 0 ta .r changes In Ufest of England liocks. ana Sao-,- W 1 . W . B . B . a ^ a of S o n , . i ^ t . I r , 3 t - f t e 0 r l „ i n o f Later! te." - * ° o l e ~ Dublin Soc. vi , 1696 #p. 105. Cclli»s~180?,vii Sp.313-Mining l&ga^ine. nana- fen u?u«y Soi»«,lM«.?.4Si- Pescrlptiire Hineraiosy. <teol. 2au.i921 .p .as-ta*rl« *t Ian is Sierra ieons. Dorwy-tfotir. Seoi. Vol.«xiv.S 0 .^?eb.-&r*liHi6- Origin and Color of Bed tons- Sept. Sbraor- -Seal, Shat is laterite? Flotl- tea. deol. 3or. ^g iand as<* the Country around Bad:.iic a M St. Austell. Fo*~ ^cictsood ana Sons, 1*2? ,61-62,74tti0-86,146-Freise- Scon. Geol., Vol.xxiv, no.3,Mayl934,pp.260&8S0-Terro Hoxa in Sao Pasela, Brazil. Fuller- Jour, Geol.1942, Vol.x,p.615- Etching of Quartz in the Interior of Conglomerates. Genth- Proc. Am. Phil. Soc. x i i i , 1673,pp.361-406- Corundum, Its Alteration. Gruner- Economic Geology, no. 17,1922,pp.422.-436. Hahnel- Jo ur.f.Praic.Ghemic lxxiii ,1306, pp.260—284— Beitrag. Zerfrage. der Kaolinbildung. Hayes- 3ull. Geo. Soc. Am. Vol.8, Mar.6,1897, p.213- Solution of Silica under Atmospheric Conditions. 16th Ann. Sept. U .S .G .S . pt.3,1895,p.547. Harrison- Geol. Mag.,1910,p.439- Laterite in British Guiana. Holland- Geol. Hag. ,1903,pp.56,63,69,- OE The Constitution, Origin and Dehydration of Laterite. A Handbook: to the Collection of Kaolin, China Clay and China Stone in Museum of Practical Geology. Holmes- Geol. Mag.,1914, p.529- Lateritic Deposits of Sosembique. Howe- Gerrnyn St. London-London 1914. Johannsen- A Descriptive Petrography of Igneous Rocks, Tol. ii- Un. of Ohicagopress,1932,pp,144,199,209-212. Johnstone- Quart. Jour. Geol. Soc. London,1689, Voi.xix. Judd- aiineralog. Mag. ,viii,1689,pp.166-196- On the Process by which a Felspar- is converted into Scapolite* Kilroe- Geol. Mag. 1906, pp.524,531-534- Laterite and Bauxite in Germany. Leighton and SaeGlintock- Jour, Geol, Vol.xxxviii, no. 1,1930- Weathered Zones of the Drift Sheets of Illinois. Leith and Mead- Henry Holt & Go. 1915, Intro, pp. xxi- Metamorphic Geology. Lenicer and Merril- Jour. Amer. Chem. Soc. Vol.S9,1317,p.2630- Solubility of Gelatinous Silica. Liebrich- Zeitchr.f.Kryst. xxiii , 1694, p.296. Lindgren- McGraw-Hill 1924,chap.xviii- The theory and application and Golloid Sehaviour. McGraw-Hill 1928,pp.362-353,372- Mineral Deposits. Scon. G e o l o g y 1 9 1 5 , pp.89-93- Origin of Kaolin. Lovering- Ko.18,1923, p.528- iiconomic Geology. Mallet- Bee. Geol. Sur. India, xiv, 1861, ppl39-14B- Iron Ores of Korth East Ulster. McCarthy- Jour. Geol. xxxiv, 1926, p.352- Iron Stained Sands and Clays. llcClaren- Geol. Sag. ,1906, p.536- The Origin of Certain Laterites. MeXee- Geol. Sag. ,1880, p.310. Mead- Jour. Geol. Vol.xv, no.3, April- Say 1907- Sedistribution of Elements in Formation. Mennell- Geol. Sag. 1909-p.S50- Bhodesian Laterite. lerrill- MacMillan 1921, pp.221 ,£i,2 & 166- Hocks, Rock-weathering and Soils Millard- McGraw-Hill,1926, pp.397-426- Physical Chemistry for Colleges. Moore and Maynard- Bcon. Geol. Vol.xxiv, no.3, 1929- Solution, Transportati-o n and Precipitation of Iron and Silica. Morse- Bull.19, 19^3, p . l , Mississippi State Geol. Survey. Passage- Report of the 6th International Geographical Congress, London 1895. Hansons- U.5 .G.S . Bull.162, p.75, 1910. Bastell- Arnold, 1927, p.241- .Physico-Chemical Geology. P.ettger-Icon. Geol. rx, Hov.1925, ,p.674- Bausite Deposits of S.JE. Alaba-ms>« . Hies- John Wiley & Sons,1927, p.2- Clays, Occurrences, Properties and Uses. Trans. Am. Ceramic. Soc.xiti,1911, pp.51-74- A Seview of the Theories - of :t,he Origin of White Residual Kaolins. Sogers and-Kerr- McGraw-Hill,IS33- 'Iain-section Mineralogy, loss and lerr- U.S.a .S,Prof. P*per 185-3, 1933- Halloysite and Allophane ,U.S.3.S.Prof. Paper 165-2, 1931, J??. 172-174- iCaolin Minerals O.S.S.S.Pjyof. Paper 185-G, 1934,- Oalloysite and Allophane. Rtobold-asgserial Jfcsi'lfc&e, .1325., -pp. 10,53-73- Bauxite and Aluminium, ' ' Simpson- Sool. Hag.,1912, pp.395,399- Laterite in Western. Australia. Smyth,G.H.- American Jour, of Science 4th series, 7ol.l9, 1905, p.282. Spencer- Geol. Sur. Georgia, 1893, p.214- The Palaeozoic Group. Spezia,G.- Jour. Ghem. Soc. Vol.76, pt.2 , 1900, p. £>95- Solubility of Quarts in Sol. of Borax or Alkaline Silicates. Stephens- U.S.S.S. Prof. Paper 165-A, 1934- Studies on the Alkalinity of some Silicate Minerals. Stephenson- Jour. Geol.xxiv, 1916, pp.191-196- The Action of Certain Alka-line Solutions on Felspar and Home blende. Stutzer- Zeitche.f,pra&. Geol. ,1905, p.337- v.'eisse £rden Zecise St. Andreas. 1 j Tarr ,\V.A.- Bcon. Geol. no.10, 1915, pp.348-367- Study of heating tests J and the light they throia on Disintegregation of Granite. | Tarr and Martin- SaeMillan 1915- College Physiography. ; Thorpe- Dictionary of Applied Cheraistry-Vol.vi, p.249. i I Van Bemmelin- Zeitchr.f.Anorg. Chemie lxvi, 1910, pp.343-357- Die Pneuma-tolutiche Xaolinverwitterung. Van Hise- MSG.S. Son.47,1204- A treaties of Metamorphism. O.S.G.S.- Mono.52, p.521. ... \ : W&lthier--VeraMl. Vessel. Srdiremde.,• xvi, 1889, p.Sl'8. Heed- U . S . G . S . , 21st. Ann. Rept. ,p .2&3, 1900. •ffeinschenk- Keues. Jahrb. ,3 .B.xv, 1302, pp.231,383- Beitrage zur SCentniss einige'r Saolinlagers tat ten, We-is- Zeit. Praict. Geol . , 1910, p.356. "Weiser- McGraw-Hill 1926, pp.34 & 107- Hydrous Oxides. Woolnough- Geol. Mag. 1915, p.385. Boon. Geol.xxiii , Dec.1928, p.887- The Origin of White Clays and Bauxite. Zsigmondy- John-Wiley & Sons- The Chemistry of Colloids. r 

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