a sulfide mineral of bismuth and tellurium (Bi₂Te₂S). It is commonly found in gold-quartz veins and contact-metamorphic deposits, as in Idu, Japan; Sorata, Bolivia; Boliden, Sweden; and Boulder county, Colo., U.S. Tetradymite is classified in a group of metallike sulfide minerals closely resembling each other in physical properties and in the hexagonal symmetry of their crystals. For detailed physical properties, see sulfide mineral (table).