Chalcocite


Also found in: Dictionary, Thesaurus, Wikipedia.
Related to Chalcocite: arsenopyrite, covellite

chalcocite

[′kal·kə‚sīt]
(mineralogy)
Cu2S A fine-grained, massive mineral with a metallic luster which tarnishes to dull black on exposure; crystallizes in the orthorhombic system, the crystals being rare and small usually with hexagonal outline as a result of twinning; hardness is 2.5-3 on Mohs scale, and specific gravity is 5.5-5.8. Also known as beta chalcocite; chalcosine; copper glance; redruthite; vitreous copper.

Chalcocite

 

(also copper glance), a sulfide mineral, Cu2S. Chalcocite usually contains admixtures of Ag; sometimes it contains Fe, Co, Ni, and As. A considerable copper deficit is occasionally observed in its composition.

Three polymorphic modifications of chalcocite are known. The most common is the orthorhombic modification, which at a temperature of 103°C alters to the hexagonal modification. Above 425°C, hexagonal chalcocite alters to the isometric modification. The structure of orthorhombic and hexagonal chalcocite is based on an extremely dense hexagonal packing of the sulfur atoms. The copper atoms occupy triangular vacancies in the plane of the densely packed “sulfur” layers.

Chalcocite is found in the form of fine-grained aggregates or phenocrysts in ores and rock. Crystals are rare, but hexagonal twins are common. Chalcocite is lead gray in color and has a metallic luster. An opaque and brittle mineral, it has a hardness of 2.5–3 on Mohs’ scale and a density of 5,780 kg/m3. It is a good conductor of electricity and an ore of copper.

The most valuable commercial accumulations of chalcocite are associated with the zones of oxidation of copper deposits, where chalcocite is found in association with bornite, chalcopyrite, and other sulfides (deposits at Bisbee, Ariz., and Butte, Mont., in the United States, at Braden and Chuquicamata in Chile, at Tsumeb in southwestern Africa, and at Dzhezkazgan in the USSR). Commercial concentrations of chalcocite occur in copper sandstones and shales. When it oxidizes at the earth’s surface, chalcocite forms cuprite, malachite, azurite, native copper, and other copper minerals.

REFERENCES

Mineraly: Spravochnik, vol. 1. Moscow, 1960.
Ramdohr, P. Rudnye mineraly i ikh srastaniia. Moscow, 1962. (Translated from German.)
Yund, R. A., and G. Kullerud. “Thermal Stability of Assemblages in the Cu—Fe—S System.” Journal of Petrology, 1966, vol. 7, no. 3.

IU. K. VOROB’EV

References in periodicals archive ?
Types of Chalcocite Considered and Deposits Analyzed
Marks, "Copper(I) tert-butylthiolato clusters as single-source precursors for high-quality chalcocite thin films: film growth and microstructure control," Chemistry of Materials, vol.
At places tetrahedrite is highly fractured and is generally replaced by chalcocite and bornite along fractures.
Hole ZFDDH11-192 was also drilled along this section to test the southern continuity of the chalcocite blanket.
The chalcopyrite pods are usually, but not always, enveloped by a rind of bornite that clearly replaces the chalcopyrite, and the bornite is commonly replaced by chalcocite in both monoclinic and hexagonal polymorphs, the latter of which suggests a minimum temperature of formation of 105[degrees]C.
According to X-ray diffraction studies this layer included five copper sulphide phases: orthorhombic anilite [Cu.sub.7][S.sub.4] and djurleite [Cu.sub.1.97]S, monoclinic chalcocite [Cu.sub.2]S, cubic talnakhite [Cu.sub.34][S.sub.32], and hexagonal yarrowite [Cu.sub.9][S.sub.8].
The EDS analyses of the grains consistently indicate a high Cu-S ratio which is suggestive of a cuprous sulphide such as chalcocite or djurleite.
Primary copper mineralisation consists of chalcocite, bornite and chalcopyrite, with secondary mineralisation (chalcocite, chrysocolla, covellite, cuprite, azurite and wad) occurring along structures.
The smelter produces blister copper (98% Cu) for shipment to the copper refinery and a slow-cooled Bessemer matte (75% Cu + Ni) which is separated at the matte separation plant into nickel sulfides (mainly heazlewoodite), metallics and copper sulfide (chalcocite).
These chalcopyrite, hypogene chalcocite and lead bearing veins type deposits, even if of small size, will be valuable addition to porphyry ores which are usually of lower grade.
The mineralogy of the milled Haib feed revealed that 98.5% of the total copper content occurred as chalcopyrite, 1% as bornite, and less than 0.5% as chalcocite, covellite, malachite and chrysocolla.
The geologists do not believe the weathered saprolite zone is connected with sulphide mineralisation below which is seen in visible chalcocite and chalcopyrite.