Chalcocite from Bristol, Conn.—Emil Javorsky/EB Inc.
Sulfide mineral, CuS, that may be an important ore of copper. It belongs to a group of sulfide minerals formed at relatively low temperatures. Chalcocite alters to native copper and other copper minerals. Valuable deposits occur in Nevada and Arizona, where other components of the original rock have been dissolved away; chalcocite is also found with bornite in sulfide veins in Montana and Namibia.