Copper(I) sulfide in the context of "Chalcocite"

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 from the Greek khalkos, meaning "copper". It is also known as redruthite, vitreous copper, or copper-glance.