Peacock Rock

Peacock ore is a pet name, referring to rocks made of the minerals bornite and chalcopyrite. The colors of peacock ore are actually tarnish upon the ore's surface. There are many unique properties that define this beautifully dirty rock.

Bornite, also known as peacock ore, is a sulfide mineral with chemical composition Cu5FeS4 that crystallizes in the orthorhombic system (pseudo-cubic). It does not display the brassy color of pyrite or chalcopyrite until tarnished but is a mottled brown/black/purple to copper-red but often is mixed with chalcopyrite. It easily tarnishes upon exposure to air and results in purple/blue iridescence on some areas.

Peacock Rock: minerals bornite and chalcopyrite.
Peacock Rock: minerals bornite and chalcopyrite.

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 as an ore for its copper content of about 63 percent by mass.

Bornite is a common copper bearing mineral, and is used as an ore of copper when found in copper deposits

Association: Chalcopyrite, pyrite, other copper and iron sulfides, garnet, calcite, wollastonite, quartz.

Peacock Rock: minerals bornite and chalcopyrite.
Category: Sulfide
Color: Copper-red or reddish-bronze on fresh surface, brown-black with bluish-purple when tarnished
Luster: Metallic when fresh, tarnishes too iridescent
Hardness: 3 - 3.25
Streak: Grayish-black
Symmetry: Orthorhombic
Tenacity: Brittle
Crystal Habit: Granular, massive disseminated grains, rare octahedrons
Location: Mainly Connecticut, Montana, Arizona, Peru, Mexico, Morocco
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