chalcociet

Chalcociet, usually spelled chalcocite, is a copper sulfide mineral with the chemical formula Cu2S. It is one of the principal copper ores and occurs in a variety of geological settings, including hydrothermal veins and the supergene enrichment zones of copper deposits. The name derives from Greek roots referring to copper.

Physically, chalcocite has a metallic luster and a gray to black color. It typically forms prismatic to granular aggregates and can occur as masses or drusy crusts. The mineral has a gray-to-black streak, a hardness of about 2.5 to 3 on the Mohs scale, and a relatively high specific gravity around 7.6 to 8.1. It shows little to no cleavage and tends to fracture conchoidally or hackly when broken.

Chalcocite forms primarily in copper-rich hydrothermal systems and is also a common product of the secondary enrichment of copper sulfide deposits. It often occurs alongside other copper minerals such as chalcopyrite, bornite, covellite, and native copper. Its high copper content—Cu2S is roughly 80 percent copper by weight—makes it a valuable ore in copper mining and processing.

Economically, chalcocite is mined as a primary copper ore in many districts worldwide. Extraction methods include open-pit and underground mining, followed by smelting or hydrometallurgical processing to produce refined copper metal. Notable production areas include major copper belts in Chile, the United States, Mexico, and Peru, among others.

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