Crystal Structure of Kristiansenite from Szklarska Poręba, Southwestern Poland Evans, R. James; Gołębiowska, Bożena; Groat, Lee A.; Pieczka, Adam
Kristiansenite, ideally Ca₂ScSn(Si₂O₇)(Si₂O₆OH), a rare late-stage hydrothermal Sc-bearing sorosilicate mineral, was found in a gadolinite-fergusonite-type pegmatite of the MI-REE subclass related to the Karkonosze granite, exposed in a quarry at Szklarska Poręba, Lower Silesia, Poland. Kristiansenite occurs in an association with andradite, epidote, allanite-(Ce), titanite, fersmite, scheelite, Sc-bearing columbite-(Fe), a YNbO₄ mineral as fergusonite-(Y) or fergusonite-(Y)-beta, silesiaite and wolframite. Single-crystal study of the mineral (R₁ of 4.96%), with composition Ca₂.₀₀(Sn₀.₉₇Sc₀.₆₉Fe³⁺₀.₁₇Mn₀.₀₅Ti₀.₀₄Zr₀.₀₃Nb₀.₀₂Al₀.₀₂Ta₀.₀₁)Σ₂(Si₂O₇)[(Si₁.₉₈Al₀.₀₂)Σ₂O₆.₀₃(OH)₀.₉₇], corroborates its triclinic structure with space group-symmetry C1, Z = 2, and unit-cell parameters a = 10.0304(5), b = 8.4056(4), c = 13.3228(6) Å, α = 90.001(3), β = 109.105(3), γ = 89.997(3)° and V = 1061.40(9) Å³. In the structure of the mineral, the Ca and Si sites are dominantly occupied with Ca and Si, whereas the M1–M4 sites are disordered. The M3 and M4 sites are occupied dominantly by Sn and subordinately Sc, whereas the M1 and M2 sites are occupied dominantly by Sc and subordinately by remaining occupants, including Sn.
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