Tetrahedrites


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Tetrahedrites

 

(fahlerz), a group of minerals (complex copper sulfides) that form an isomorphic tennantite-tetrahedrite series with the chemical formula nCu12As4S13 + mCu12Sb4S13. The pure members of the series are rarely encountered. Usually the composition is complicated by impurities of Ag, Zn, Fe, and Hg, which replace Cu; and Bi, which replaces As and Sb. Depending on their composition, tetrahedrites are divided into the following varieties: argen-totennantite and freibergite (which contain Ag), sandberger-ite and binnite (which contain Zn and Ag), ferrotennantite and ferrotetrahedrite (which contain Fe), schwatzite (which contains Hg), and annivite (which contains Bi). The structure is complex and of the skeleton type. They crystallize in a cubic system, forming tetrahedral—less frequently cubic and octahedral—crystal faces. Individual grains, granular irregular aggregates, and ore masses are more often encountered. The color is steel gray to iron black. The luster on a fresh fracture is metallic, and the ores tarnish or fade rapidly in air (hence the German name, Fahlerz, from fahl, “faded,” and the Russian bleklye rudy, from bleknut’, “to fade”). Their hardness on the mineralogical scale is 3–4; their density is 4,400–5,100 kg/m3. Tetrahedrites are formed in hydrothermal ore bodies of various genetic types. The major accessory minerals of tetrahedrites are galenite, sphalerite, chalcopyrite, pyrite, quartz, barite, and calcite. They erode readily on the surface and turn into malachite, azurite, cuprite, and so on. The largest deposits of tetrahedrites known are in the USSR (in the Urals, the Caucasus, the Altai, and Kazakhstan); the largest abroad are in Hungary, Great Britain, and the USA.

REFERENCE

Mineraly: Spravochnik, vol. 1. Moscow, 1960.

G. P. BARSANOV

References in periodicals archive ?
In 1999 there was a find of beautiful matrix specimens with transparent, bright red, platy hubnerite crystals to 2 cm growing on quartz, with colorless fluorite cubes, tetrahedrite, and transparent orange sphalerite crystals to 1 cm resembling scheelite.
Fine tetrahedrite specimens, with very lustrous, simple tetrahedral crystals to 2 cm associated with sphalerite, were found in August 2001.
Tetrahedrite from Milpo generally occurs in small crystals; good specimens are very rare, but can be very aesthetic.
In some cases the quartz is accompanied by tetrahedrite crystals to 1 cm or by sphalerite crystals completely covered by a chalcopyrite crust.
When I got there, Graham was pulling out one of the finest tetrahedrite specimens I have ever seen from Colorado.
The 14 x 25-inch pocket in question here produced an estimated $12,000 in fine tetrahedrite, fluorite and rhodochrosite specimens.
Increasingly, good specimens of fluorite, green apatite and tetrahedrite were also encountered: "One tetrahedrite measured 2 inches across and was perched on small quartz crystals.
Meanwhile, work on the Tetrahedrite Drift by Scott Betz takes up where it left off in the '91 season.
The Colqui mine and vein has argentiferous tetrahedrite as its principal ore mineral, and it also contains sphalerite, galena, rhodochrosite, realgar and quartz.
Tetrahedrite occurred as large, bright crystals on a microcrystalline drusy quartz and pyrite matrix.
Sphalerite is abundant, chalcopyrite is common, galena is minor, and tetrahedrite is rare and As-rich.
The beginning of chalcopyrite crystallization was later than that of sphalerite, galena and pyrite within stage I, and tetrahedrite deposition corresponds mainly to a single well-defined event within stage III.