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TETRADYMITE

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Originally appearing in Volume V26, Page 670 of the 1911 Encyclopedia Britannica.
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TETRADYMITE , a See also:

mineral consisting of See also:bismuth telluride and sulphide, Bi2Te2S, also known as " telluric bismuth." Sometimes See also:sulphur is absent and the See also:formula is then Bi2Tea; traces of See also:selenium are usually See also:present. Crystals are See also:rhombohedral, but are rarely distinctly See also:developed; they are twinned together in See also:groups of four; hence the name of the mineral, from the See also:Greek, rerpaSupos, fourfold. There is a perfect cleavage parallel to the basal See also:plane; and the mineral usually occurs in foliated masses of irregular outline. The See also:colour is See also:steel-See also:grey, and the lustre metallic and brilliant. The mineral is very soft (H = 1) and marks See also:paper; the specific gravity is 7.2 to 7.6. It was first found, in 1815, at Telemarken in See also:Norway; crystals are from Schubkau near Schemnitz in See also:Hungary. It often occurs in See also:quartz associated with native See also:gold. Other See also:species very similar to tetradymite, but with different formulae, are: joseite, from See also:San Jose near Marianna in See also:Brazil; grunlingite (Bi,SaTe), from Caldbeck Fells in Cumber-See also:land; and wehrlite, from Hungary. (L. J.

End of Article: TETRADYMITE

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TETRAGRAMMATON (rerrapa, four; ypciµµa, letter)

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