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TETRAHEDRITE
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TETRAHEDRITE , a See also:mineral consisting typically of See also:copper sulph-antimonite, CuaSbSa, but often of complex See also:composition. The copper is usually isomorphously replaced by variable amounts of See also:silver, See also:iron, See also:zinc, See also:mercury, See also:lead or See also:cobalt, and the See also:antimony by See also:arsenic or See also:bismuth. In See also:general, the See also:formula is R'6X2Se-}-xR"6X2S9, where R' = Cu, Ag; X= Sb, As, Bi; R" = Fe, Zn, and x is a small fraction, often 31-0 or . Numerous See also:special names have been applied to varieties differing in chemical composition; the arsenic See also:compound, CuaAsS3, is known as tennantite (after See also:Smithson See also:Tennant). The old See also:German name Fahlerz includes both tetrahedrite and tennantite, and so does the See also:term " See also:grey copper ore of miners. Tetrahedrite is an important ore of copper, the formula CuaSbSa, cot responding with 57'5 per cent. of this See also:metal; it is also largely worked as an ore of silver, of which See also:element it sometimes contains as much as 30 per cent. Well-See also:developed crystals are of frequent occurrence; they belong to the See also:tetrahedral class of the cubic See also:system, and their tetrahedral See also:form is a very characteristic feature of the mineral, which for this See also:reason was named tetrahedrite. Fig. r Crystals of Tetrahedrite. shows a See also:combination of a See also:tetrahedron and a triakis-tetrahedron 12111, and fig. 2 a tetrahedron with the rhombic See also:dodecahedron. Interpenetrating twinned crystals sometimes occur. The See also:colour is See also:steel-grey to iron-See also:black, and the lustre metallic and brilliant. The streak is usually black; sometimes, however, it is dark See also:cherry-red, and very thin splinters of the mineral then transmit a small amount of See also:blood-red See also:light. The hardness is 4, and the specific gravity varies with the composition from 4.4 to 5.1. There is no cleavage, and the fracture is conchoidal. The material is often very impure owing to intimate inter-mixture with chalcopyrite.
Tetrahedrite occurs in metalliferous See also:veins associated with chalcopyrite, See also:pyrites, See also:blende, See also:galena, &c. See also:Fine See also:groups of crystals, coated on their See also:surface with brassy or brilliantly tarnished chalcopyrite, were formerly found at Herodsfoot mine, near See also:Liskeard in See also:Cornwall. See also:Good crystals are also met with at Kapnik-Banya in See also:Hungary, in the Harz, See also:Peru, and other places. Tennantite occurs as small crystals of cubic or dodecahedral See also:habit in many
Cornish copper mines, especially in the neighbourhood of See also:Redruth : it is also found as small, brilliant crystals very See also:rich in faces in the See also: Additional information and CommentsThere are no comments yet for this article.
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