Redetermination of ruizite, Ca2Mn3+2[Si4O11(OH)2](OH)2·2H2O

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Marco E. Ciriotti
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Redetermination of ruizite, Ca2Mn3+2[Si4O11(OH)2](OH)2·2H2O

Messaggio da Marco E. Ciriotti » gio 30 giu, 2016 12:21

Referenza:
▪ Fendrich, K.V., Downs, R.T., Origlieri, M.J. (2016): Redetermination of ruizite, Ca2Mn3+2[Si4O11(OH)2](OH)2·2H2O. Acta Crystallographica, E72, 959-963.

Abstract:
The crystal structure of ruizite, ideally Ca2Mn3+2[Si4O11(OH)2](OH)2·2H2O was redetermined based on single-crystal X-ray diffraction data of a natural sample from the Wessels mine, Northern Cape Province, South Africa, in space group C2. All non-H atoms were refined with anisotropic displacement parameters and all hydrogen atoms were located, improving upon previous results and yielding a significantly lower R factor.

The crystal structure of ruizite, ideally Ca2Mn3+2[Si4O11(OH)2](OH)2·2H2O [dicalcium dimanganese(III) tetra­silicate tetra­hydroxide dihydrate] was first determined in space group A2 with an isotropic displacement parameter model (R = 5.6%) [Hawthorne (1984). Tschermaks Mineral. Petrogr. Mitt. 33, 135-146]. A subsequent refinement in space group C2/m with anisotropic displacement parameters for non-H atoms converged with R = 8.4% [Moore et al. (1985). Am. Mineral. 70, 171-181]. The current study reports a redetermination of the ruizite structure by means of single-crystal X-ray diffraction data of a natural sample from the Wessels mine, Kalahari Manganese Field, Northern Cape Province, South Africa. Our data (R1 = 3.0%) confirm that the space group of ruizite is that of the first study rather than C2/m. This work improves upon the structure reported by Hawthorne (1984) in that all non-H atoms were refined with anisotropic displacement parameters and all hydrogen atoms were located. The crystal structure consists of [010] chains of edge-sharing MnO6 octa­hedra flanked by finite [Si4O11(OH)2] chains. The Ca2+ cations are situated in the cavities of this arrangement and exhibit a coordination number of seven.

_cell_length_a 9.0360(3)
_cell_length_b 6.1683(2)
_cell_length_c 11.9601(4)
_cell_angle_alpha 90
_cell_angle_beta 91.433(2)
_cell_angle_gamma 90
_cell_volume 666.41(4)
_cell_formula_units_Z 2
Marco E. Ciriotti

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