Bornite is a sulfide mineral with chemical composition Cu5FeS4
that crystallizes in the orthorhombic
system. It has a brown to copper-red
color on fresh surfaces that tarnishes to various iridescent shades of blue
to purple in places. Its striking iridescence gives it the nickname peacock
copper or peacock ore.
Bornite is an important copper ore mineral and occurs widely
in porphyry copper deposits along with the more common chalcopyrite.
Chalcopyrite and bornite are both typically replaced by chalcocite and
covellite in the supergene enrichment zone of copper deposits. Bornite is also
found as disseminations in mafic igneous rocks, in contact metamorphic skarn
deposits, in pegmatites and in sedimentary cupriferous shales. It is important
for its copper content of about 63 percent by mass and is found in Arizona,
Butte, Montana, and Mexico.
It has been reported since 1725, but in 1845 it was named for
Austrian mineralogist Ignaz von Born (1742–1791).
Category Sulfide mineral Chemical formula Cu5FeS4
Identification Molecular weight 342.681 Color Copper red, bronze brown, purple
Crystal habit Granular, massive, disseminated - Crystals pseudocubic,
dodecahedral, octahedral Crystal system Orthorhombic - Dipyramidal (2/m 2/m
2/m) Twinning Penetration twins on [111] Cleavage
Imperfect on [111] Fracture
Conchoidal, Mohs Scale hardness 3 -
3.25, Luster Metallic Streak grayish
black, Specific gravity 4.9 - 5.3,
Refractive index Opaque Other characteristics Magnetic after heating.
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