Gray copper ores

GRAY COPPER ORES (named according to the pale lustre * EN: gray copper ore, fahlore, fahlite; DE: Fahlerze; FR: cuivre gris, spaniolite; ES: cobre gris; RU: блеклые руды) is the group of the minerals, complex sulfides (sulfosalts) of copper, which are forming the isomorphous series with the Cu12(Sb,As)4S13 general formula. The end members of the series are the antimony variety, namely, tetrahedrite, and the arsenic variety, namely, tennantite. The impurities are: Zn, Fe, Ag, less often Hg, Ni, So, which are substituting Cu, and also Bi, Se, and Te, which are substituting Sb, As, and S.

Depending on the content of the impurities, they distinguish the freibergite and argento-tennantite (Ag), binnite and sandbergerite (Zn and Ag), ferro-tetrahedrite and ferro-tennantite (Fe), schwazite (Hg), annivite (Bi), and so on. They crystallize themselves into the cubic crystal systems; the structure of the gray copper ores is of the framework type. They form the crystals of the tetrahedral, less often cubic and octahedral habit. More often, there may be found the individual grains and granular aggregates. There are known the twins of penetration and contact, and also the epitaxial intergrowths with chalcopyrite, stannite, sphalerite, and galena. The colour is from steel-gray to iron-black, under the microscope within the polished sections gray, sometimes olive-brown. The lustre on the fresh fracture is metallic, the cleavage is absent. The hardness is 3-4.5 (tennantite is harder, than tetrahedrite). The density is from 4600 (tennantite) to 5400 kilograms per cubic metre (tetrahedrite). There are characteristic the brittleness and poor conductivity of electricity. The gray copper ores are the hydrothermal minerals. Their main satellites are galena, sphalerite, chalcopyrite, pyrite, quartz, barite, calcite. They are easily weathered, being substituted by malachite, azurite, cuprite, and so on. The largest deposits within the USSR are known at the Urals, Caucasus, Altai, and within Kazakhstan, and abroad within Hungary, Great Britain, USA. There has the industrial importance only tetrahedrite, which, in case of the high concentrations, belongs to the composition of the copper ores and antimony ores.