Tetradymite
a rhombohedral mineral found sometimes in crystals, but more frequently granular, massive, or foliated, often with auriferous ores; luster, bright metallic; color, pale steel-gray; in thin laminæ, flexible. Composition: Somewhat variable, but consists principally of bismuth and tellurium. Dana divides as follows: (a) Free from sulphur, with formula Bi2Te3; (b) Sulphurous, with formula, and (c) Seleniferous. Also the same as joseite and wehrlite.