1. Redetermination and new description of the crystal structure of vanthoffite, Na6Mg(SO4)4.
- Author
-
Balić-Žunić, T., Pamato, M. G., and Nestola, F.
- Subjects
CRYSTAL structure ,TETRAHEDRA ,POLYHEDRA ,MINERALS ,SPACE groups ,DIMERS ,SULFATES - Abstract
The crystal structure of vanthoffite {hexasodium magnesium tetrakis[sulfate(VI)]}, Na
6 Mg(SO4 )4 , was solved in the year 1964 on a synthetic sample [Fischer & Hellner (1964). Acta Cryst. 17, 1613]. Here we report a redetermination of its crystal structure on a mineral sample with improved precision. It was refined in the space group P21 /c from a crystal originating from Surtsey, Iceland. The unique Mg (site symmetry 1̅) and the two S atoms are in usual, only slightly distorted octahedral and tetrahedral coordinations, respectively. The three independent Na atoms are in a distorted octahedral coordination (1×) and distorted 7-coordinations intermediate between a `split octahedron' and a pentagonal bipyramid (2×). [MgO6 ] coordination polyhedra interchange with one half of the sulfate tetrahedra in <011> chains forming a (100) meshed layer, with dimers formed by edge-sharing [NaO7 ] polyhedra filling the interchain spaces. The other [NaO7 ] polyhedra are organized in a parallel layer formed by [010] and [001] chains united through edge sharing and bonds to the remaining half of sulfate groups and to [NaO6 ] octahedra. The two types of layers interconnect through tight bonding, which explains the lack of morphological characteristics typical of layered structures. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF