Bornite
Image: Darla Sondrol (CC0)
Mineral NameBornite
Chemical FormulaCu5FeS4
Mohs Hardness3
Crystal Systemorthorhombic
Lustermetallic
Streak Colorgrayish black
Cleavagepoor/indistinct on {111}
Fractureconchoidal to uneven
Specific Gravity5
Colorscoppery red, brown, iridescent purple
Transparencyopaque
Type LocalityWorldwide, notable localities include Cornwall (England), Butte (Montana, USA), and Messina (South Africa).
Mineral GroupSulfides
Usescopper ore
Associated Mineralschalcopyrite, pyrite, chalcocite, covellite, quartz
Raritycommon
Description
This 9 cm specimen of bornite displays a coppery red to brown color on fresh surfaces, which readily tarnishes to an iridescent purple, earning it the nickname 'peacock ore'. It typically forms massive aggregates rather than distinct crystals.
Geological Context
Bornite is a primary copper ore mineral found in hydrothermal veins, porphyry copper deposits, and sedimentary copper deposits. It often forms at high temperatures and can be a product of both primary mineralization and secondary alteration.
