Copper

Formula:  Cu

Origin of name:  From Latin cuprum - metal form Cyprus

Crystal system:  Cubic

Crystal class:  4/m -3 2/m

Twinning:  Common on {111}, contact, penetration, or cyclic

Unit cell: a = 3.615 Å

Colour:  Copper red, brown; pale rose when fresh, pale pink

Diaphaneity:

Luster:  Metallic

Habit:  Crystals cubic, octahedral, dodecahedral, tetrahexahedral; arborescent, wirelike, massive, powdery

Hardness:  2.5 to 3

Specific gravity:  8.94

Cleavage:  None

Tenacity:  malleable and ductile; hackly fracture

Streak:  Pale red

Synonyms/varieties:  Whitneyite (As-rich var.)

Comments: Commonly associated with porous zones in mafic extrusive rocks, less commonly in sandstones and shales, where the copper probably was of hydrothermal origin, precipitated as the result of oxidising conditions; in the oxidised zone of large, disseminated copper deposits as the result of secondary processess.