Natural Tellurides

a class of minerals comprising natural compounds of tellurium with heavy metals (Bi, Au, Ag, Pd, Cu, Sb, Pt); analogues of sulfides and selenides. Natural tellurides are characterized by complex, nonstoichiometric compositions. In certain of the tellurides, tellurium may be isomorphously replaced by S, Bi, or Sb; in the cation part, it is not uncommon to find two metals present simultaneously. Natural tellurides crystallize mainly in high-order systems.

Approximately 40 natural tellurides are known. Among them are altaite, PbTe; tellurobismuthite, Bi₂Te₃; tetradymite, Bi₂Te₂S; calaverite, AuTe₂; hessite, Ag₂Te; moncheite, Pt(Te,Bi)₂; kotulskite, Pd(Te,Bi); and merenskyite, Pd(Te,Bi)₂. Tellurides may occur in association with sulfides in the form of microscopic granular segregations.

Natural tellurides have a marked metallic luster and electrical conductivity and a high density (6,000–7,000 kg/m³ and higher). Hardness on Mohs’ scale is 2–3. Natural tellurides are encountered in pyrite, copper-nickel, and copper-molybdenum deposits and in deposits of complex ores. In the comprehensive processing of sulfide ores, natural tellurides serve as a source for the extraction of noble metals (Au, Ag, Pt, Pd) and of tellurium itself.