Abstract

The valency formulae of minerals in the system Cu-Fe-Sn-S were determined with the aid of electron probe microanalysis and of the Mössbauer effect study of 57Fe and 119Sn at temperatures of 80°K and 293°K. The formulae of stannite, stannoidite, and mawsonite can be expressed as Cu1+2(Fe2+, Zn2+) Sn4+S2-4, Cu1+8Fe3+2(Fe2+, Zn2+) Sn4+2S3-12 and Cu1+6Fe3+2 Sn4+S2-8 respectively. Zn was found to substitute only for the ferrous ion. Mawsonite contains no zinc.

The quadrupole splittings and isomer shifts could be rationalized with crystal field effects caused by the differences in site symmetry around the Fe and Sn atoms. Quadrupole splittings and isomer shifts of 119Sn indicate that the (SnS4)-tetrahedron of these specimens is strongly covanently bonded, and that it may be regarded as a chemical radical bearing sp3 hybrid orbitals. Site symmetries around tin atoms in these structures are similar.

The most probable space group of mawsonite is I42m, I4mm, 1422, or I4122, based on its X-ray powder diffraction pattern and the site symmetries of tin and iron ions determined from the Môssbauer effect study.

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