Chalcocite


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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 ?
Drill holes ZFDDH11-190 and ZFDDH11-194 were drilled on the southern portion of this section, 150 and 250 metres south of ZFDDH11-213 respectively, where weak chalcocite enrichment occurs.
The Northwest Zone is a northwest trending, steeply to sub-vertical northeast dipping zone containing disseminated, fracture and vein controlled native copper, chalcocite, bornite, chalcopyrite and malachite mineralisation.
A supergene sulphide transition zone is typically found from about 35 to 38 metres downhole consisting of chalcocite and pyrite with minor malachite.
Chalcocite mineralization in vertical hole QMC-02 was extended by angle holes drilled to the east and west from the same collar location.
Forward-looking statements in this news release include, but are not limited to: that the View Sites claims incorporate projected extensions of the MAN Area copper-zinc-silver-gold sulfide mineralization, as well as continuation of the leachable oxide copper and chalcocite copper deposits overlying the MAN Area sulfide zone; that, had the Debentures not been redeemed in full for cash, that potentially significant equity dilution could have resulted; and, that the Company is aggressively pursuing new opportunities and moving ahead with exploration plans at the Gavilanes gold project.
We believe that these may have the potential to host chalcocite enrichment, as well as underlying primary mineralization.
A program of triple tube diamond drilling will determine how much of this may be soft chalcocite and whether significant cavities may be present.
The hole contains chalcopyrite-bearing skarn to a depth of approximately 120 metres, below which is secondary chalcocite and mixed chalcocite/chalcopyrite to the bottom of the hole at 191.
Approximately 20,000 feet of the planned and permitted drill program has been designed to further delineate the extent of the leachable chalcocite resource, and provide additional drill and assay data for an independent NI 43-101 resource estimate to be completed by the end of the year.
Malachite and chalcocite as well as minor occurrences of molybdenum, galena and sphalerite in quartz veinlets occur also in the volcanics (MINFILE 224 - SAT showing).
Drill holes CO-06-O53 and -055 are 100 metre step-out holes in the Constancia Zone that contain mixed chalcocite and chalcopyrite, with the chalcocite content decreasing with depth.