ANTIMONIDE

any member of a rare mineral group consisting of compounds of one or more metals with antimony (Sb). The coordination of the metal is virtually always octahedral or tetrahedral; i.e., in the former, each metal ion occupies a position within an octahedron composed of six negatively charged antimony ions, whereas, in the latter, the metal ion is surrounded by four negatively charged neighbours that are arranged tetrahedrally. The crystal structure of octahedral coordination is identical to that of the sulfide mineral galena; that of tetrahedral coordination corresponds to the structure of another member of the same mineral group, argentite. Two common antimonides are dyscrasite (Ag3Sb) and stibiopalladinite (Pd5Sb2). Dyscrasite exhibits a distinct orthorhombic symmetry. It is an important silver ore that occurs in deposits of hydrothermal origin associated with intrusive igneous rocks; significant amounts are found at Cobalt, Ont., Can., and at Broken Hill, N.S.W., Australia. Stibiopalladinite exhibits trigonal symmetry. It is a principal palladium mineral that occurs in various deposits associated with platinum, pyrrhotite, and chalcopyrite. It has been found in the Bushveld Complex, S.Af., at Kambalda, W.Aus., and at Norilsk, Russia. Other antimonides include aurostibite (AuSb2) and breithauptite (NiSb). All antimonides have a metallic lustre, are opaque, and have high specific gravity and intermediate to low hardness.