It is rare for copper to form crystals; when it does, they take the form of cubes, octahedra, or dodecahedra. The usual habits are dendritic and massive. Copper can also form in wires.
Color is a key identification feature and is copper-red or pale rose-red on fresh surfaces.
It tarnishes to copper-brown. The streak is copper-red. Copper is an opaque mineral. Its luster is metallic.

FORMATION Forms chiefly in the regions where veins containing copper sulfides have been altered.

TESTS It is soluble in nitric acid.

Group: NATIVE ELEMENTS

Composition: Cu

Classification: 2½–3

SG: 8.94

Cleavage: None

Fracture: Hackly