Chalcocite

Mineral formula: Cu₂S

Mineral group: member of the Chalcocite-Digenite group

Crystal system: monoclinic

Crystal habit: massive, or tabular prismatic.

Cleavage: poor / indistinct

Fracture: conchoidal

Color: blue-black, gray, black, or black-gray

Luster: metallic, sub-metallic

Diaphaneity: opaque

Moh’s scale hardness: 2 ½ - 3

Streak: blackish lead gray

Specific gravity: 5.5 – 5.8

Named after: the Greek word, "chalkos", copper, in 1832 by François Sulpice Beudant. This mineral was known by a wide variety of names previously, including “chalcosine”. In 1868, James D. Dana and George J. Brush renamed this material "chalcocite".

Geological occurrence: A secondary mineral in or near the oxidized zone of copper sulfide deposits. Hexagonal above 105°C ('High-chalcocite').