tetradymite

noun

te·​trad·​y·​mite

tə̇‧ˈtradəˌmīt

plural -s

: a mineral Bi₂Te₂S consisting of a telluride and sulfide of bismuth, sometimes containing selenium, being pale steel gray in color and of a metallic luster, and occurring usually in foliated masses (hardness 1.5–2, specific gravity 7.2–7.6)

Word History

Etymology

Late Greek tetradymos fourfold, from Greek tetra- + didymos twin; from its occurrence in compound twin crystals

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