Tetradymite - Glacier Gulch, Smithers, Omenica Mining Division, British Columbia , Canada . Found in 1934 (45x26mm) — Photo: Didier Descouens · CC BY-SA 3.0
Tetradymite
A bismuth telluride-sulfide — 'telluric bismuth' — silvery flexible laminae in hydrothermal veins.
Intro adapted from Wikipedia (CC BY-SA).
Tetradymite is an IMA-recognized mineral species in the sulfide class, with the chemical formula Bi₂Te₂S.
It crystallizes in the hexagonal crystal system (space group R-3). It is a member of the Tetradymite structural group.
Key properties: Mohs hardness 1.5–2; specific gravity 7.3; Pale steel-gray streak; Metallic, splendent on fresh surfaces. Anisotropism: Weak. R1 –R2: (400) 51.9–56.8, (420) 52.0–56.9, (440) 52.0–57.0 luster.
IMA symbol Ttd, grandfathered status — known before the IMA’s founding, named in 1831.
Found in hydrothermal gold-quartz veins of medium to high temperature of formation; also in contact metamorphic deposits.
It is found associated with Tellurium, tellurobismuthite, gold, silver, bismuth, hessite, petzite, calaverite, matildite, altaite, pyrite, pyrrhotite, galena, sphalerite, arsenopyrite.
Its name comes from the Greek for fourfold and twin, an allusion to the twin crystals.