Bornite

Formula:  Cu₅FeS₄

Origin of name:  For Ignaz Born, Austrian mineralogist (1742-1791)

Crystal system:  Orthorhombic

Crystal class:  2/m 2/m 2/m

Twinning:  On {111}, penetration

Unit cell: a = 10.94 Ǻ, b = 21.86 Ǻ, c = 10.95 Ǻ

Colour:  Copper-red or bronze, tarnishes iridescent purplish

Diaphaneity: Opaque

Luster:  Metallic

Habit:  Crystals cubic, octahedral or dodecahedral, rare; massive, granular

Hardness:  3

Specific gravity:  5.079

Cleavage:  1; {111} in traces

Tenacity:  Conchoidal to uneven

Streak:  Light grayish black

Synonyms/varieties:  Erubescite, peacock ore, phillipsine

Comments: Found associated with and disseminated in mafic igneous rocks, in contact metamorphic (skarn) deposits, in pegmatites, in intermediate to high-temperature hydrothermal deposits and in sedimentary cupriferous shales