Chalcocite (/ˈkælkəˌsaɪt/), copper(I) sulfide (Cu2S), is an important copper ore mineral. It is opaque and dark gray to black, with a metallic luster. It has a hardness of 2.5–3 on the Mohs scale. It is a sulfide with a monoclinic crystal system.
The term chalcocite comes from the alteration of the obsolete name chalcosine, from the Greek khalkos, meaning "copper". It is also known as redruthite, vitreous copper, or copper-glance.
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