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Crystal structure determination of anandite-2M mica by T. J. Bujnowski; S. Guggenheim; T. Kato is a Earth and Planetary Sciences article available to read on EtoBox.

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Anandite, a trioctahedral mica, has an ideal chemical formula of Ba(FeMg) 3 (SiFe 3+ )O 10 (OH)S and a microprobe-derived formula of (Ba 0.96 K 0.03 Na 0.01 ) Σ=1.00 (Fe 2+ 2.01 Mg 0.46 Fe 3+ 0.28 Al 0.10 Mn 3+ 0.04 Mn 2+ 0.04 Ti 0.01 ) Σ=2.93 (Si 2.60 Fe 3+ 1.40 ) Σ=4.00 O 10 [(OH) 0.96 S 0.84 Cl 0.16 F 0.04 ] Σ=2.00 , where S 2-primarily substitutes for (OH) -. A single-crystal, X-ray structure determination of anandite-2M was refined to R 1 = 0.0443 and wR 2 = 0.1232 on F 2 in space group Am. Cell parameters are: a = 5.4431(3), b = 9.4719(6), c = 20.042(1) Å, and β = 95.046(1)°. Layer stacking is analogous to a 1M stacking pattern (parallel unidirectional a/3 shifts within layers and octahedral set I only occupied), however cation order and (S,OH) positional disorder produce a two-layer repeat with β equaling ~95°. Subgroup symmetry of Am results from tetrahedral sheets within layers that are non-centrosymmetric with unequal compositions (Si 0.61 Fe 3+ 0.39 vs. Si 0.79 Fe 3+ 0.21 ) and thicknesses (difference of 0.209 Å), and there is positional and site-occupancy disorder (four sites with S of 0, 30, 52, and 58%) of (S,OH). Characteristics of anandite-2M, which are similar to t

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Author

T. J. Bujnowski; S. Guggenheim; T. Kato

Publisher

Mineralogical Society of America

Published

2009

Language

EN

Field

Earth and Planetary Sciences (Physical Sciences)