Redetermination of ruizite, Ca(2)Mn(3+) (2)[Si(4)O(11)(OH)(2)](OH)(2)·2H(2)O

The crystal structure of ruizite, ideally Ca(2)Mn(3+) (2)[Si(4)O(11)(OH)(2)](OH)(2)·2H(2)O [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 (R (1) = 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 MnO(6) octa­hedra flanked by finite [Si(4)O(11)(OH)(2)] chains. The Ca(2+) cations are situated in the cavities of this arrangement and exhibit a coordination number of seven.