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Tetradymite is a mineral consisting of bismuth, tellurium and sulfide, Bi2Te2S, also known as telluric bismuth. If sulfur is absent the mineral is tellurobismuthite and the formula is then Bi2Te3. Traces of selenium are usually present.
Additional recommended knowledge
Crystals are rhombohedral, but are rarely distinctly developed; they are twinned together in groups of four; hence the name of the mineral, from the Greek for fourfold. There is a perfect cleavage parallel to the basal plane and the mineral usually occurs in foliated masses of irregular outline. The color is steel-grey, and the lustre metallic and brilliant. The mineral is very soft (H = 1.5 - 2) and marks paper. The specific gravity is 7.2 to 7.9.
The type locality is Zupkov (Zsubko; Schubkau), Stredoslovenský Kraj, Slovak Republic where it was reported in 1831. It was first found, in 1815, at Telemarken in Norway; crystals are from Schubkau. It often occurs in quartz associated with native gold.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Tetradymite". A list of authors is available in Wikipedia.|