chalcocit

Chalcocite, sometimes spelled chalcocit, is a copper sulfide mineral with the chemical formula Cu2S. It is one of the most copper-rich sulfide minerals and occurs as a primary ore in some deposits as well as as a secondary, supergene product formed during enrichment of copper-bearing systems. Its high copper content—about 79.8 percent copper by weight—makes it a significant ore in copper mining.

Physically, chalcocite has a metallic luster and a gray to bluish-black to black coloration. It is relatively soft, with a Mohs hardness of about 2.5 to 3, and it is commonly found in massive, granular, or lamellar aggregates. The streak is dark gray to black, and its specific gravity ranges roughly from 7.6 to 7.9. Crystals, when present, are typically small and may exhibit a tetragonal habit, though chalcocite most often occurs as aggregated masses rather than well-formed crystals.

In terms of formation and occurrence, chalcocite is commonly associated with other copper minerals such as chalcopyrite, bornite, covellite, and malachite. It forms in hydrothermal veins and in oxidized zones where copper minerals are mobilized and re-deposited under reducing conditions, a process characteristic of supergene enrichment in porphyry copper deposits.

Economically, chalcocite is an important copper ore due to its high copper content. It can be exploited directly in some deposits, and its presence often indicates zones of enriched copper mineralization. The mineral is named from Greek roots related to copper, reflecting its composition and metallic character.