Crystal chemistry and crystallography of some minerals in the tetradymite group

Selen-tellurium is a mixture of the minerals selenium and tellurium. The atoms in stibarsen are ordered (completely or partially) so that the correct chemical formula is AsSb. Matildite AgBiS2, bohdanowiczite AgBiSe2, and volynskite AgBiTe2, show atomic ordering in space group P3ml with unit-cell dimensions similar to those oftsumoite, BiTe. The S and Te atoms are apparently disordered in ingodite to yield the chemical formula Bi(S,Te) and in sulphotsumoite to yield the chemical formula Bi(Te,S). The unnamed mineral of Aksenov et al. (1968) seems to be tellurian tsumoite, (Bio.58 Teo.42)Te.The synthetic composition of Godovnikov et al. (1966) is equivalent to bismuthian tsumoite, Bi(Teo.75Bio.25)' Platynite is possibly plumbian sulfurian nevskite, (Bio.650Pbo.345)(Seo.657So.348)' Kawazulite, Bi2SeTe2, is isostructural with tetradymite. Csiklovaite is a mixture of tetradymite and bismuthinite. The chemical formula ofskippenite is probably BiiSe,Te,S)3' like that of tellurian paraguanajuatite. The Se and S are disordered in laitakarite to yield the chemical formula Bi.(Se,S)3' As S and Te ordering was not observed in joseite or joseite-B, there is possibly a complete solid solution series from tellurian ikunolite, Bi4(S,Te)3' to sulfurian pilsenite, Bi4(Te,S)3' The unnamed mineral ofYingchen (1986) is apparently tellurian ikunolite. Rucklidgeite, Bi3Te4, has an antipilsenite, Bi4Te3, structure type. The unnamed mineral of Haraficzyk (1978) is rucklidgeite.