CRYSTAL STRUCTURE OF NATURAL Ag-Cu-Pb-Bi SULFIDE
S. V. Borisov, N. V. Pervukhina, N. V. Kurat’eva, S. A. Magarill, B. M. Kuchumov
Nikolaev Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
Keywords: Ag-Cu-Pb-Bi-сульфид, структура, кристаллографический анализ, микродвойникование, катионные и анионные подрешетки, Ag-Cu-Pb-Bi sulfide, structure, crystallographic analysis, microtwinning, cation and anion sublattices
Abstract
The crystal structure of a natural sulfide Cu3,44Ag0,56Pb2Bi6S13 ( Сmcm , Z = 4, a = 3.973(1) Å, b = 13.370(2) Å, c = 42.182(7) Å, R = 0.059) is determined. The structure has seven cation positions: two of them (Cu and Ag) are in a tetrahedral environment of sulfur atoms; one (Pb), in a special position (mm2), has a coordination polyhedron in the form of a bicapped trigonal prism; and the other cation positions are surrounded by sulfur atoms forming distorted octahedra. The mirror symmetry plane perpendicular to the c translation causes microtwinning by cutting a layer of trigonal prisms framed by tetrahedron ribbons. These layers are divided by those composed by edge-linked octahedra with a diagonal ribbon of five octahedra ( N = 5). The cation and anion positions are ordered by individual sublattices with pseudohexagonal subcells on the m planes perpendicular to the a translation, which concentrate the positions of all the atoms. Supposedly, this natural sulfide is the previously described (1885) yet unconfirmed alaskaite mineral from the lillianite-heyrovskyite homological series and may be isostructural to the ourayite mineral.
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