Trisha Shetty (Editor)

Tetradymite

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Category  Sulfide mineral
Strunz classification  2.DC.05c
Crystal system  Trigonal
Formula (repeating unit)  Bi2Te2S
Dana classification  02.11.07.01
Tetradymite
Crystal class  Hexagonal scalenohedral (3m) H-M symbol: (3 2/m)

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.

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-gray, and the luster 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), Stredoslovensk√Ĺ Kraj, Slovak Republic where it was reported in 1831. It was first found, in 1815, at Telemark in Norway. It often occurs in high temperature hydrothermal quartz veins associated with native gold and in contact metamorphic deposits.

References

Tetradymite Wikipedia


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