Bornite

Bornite is a copper iron sulfide mineral (Cu5FeS4) best known as peacock ore for the brilliant iridescent purple, blue, and red colors that develop on its tarnished surface. Freshly broken bornite is a coppery brown or bronze, but it quickly tarnishes to its signature peacock sheen.

It is an important ore of copper, often found alongside chalcopyrite and other copper sulfides. The vivid tarnish makes it a favorite among mineral collectors and a popular tumbled stone.

Much material sold as peacock ore in shops is actually chalcopyrite treated with acid to enhance iridescence; genuine bornite shows naturally rich purple-blue colors.

Bornite forms in hydrothermal copper deposits, porphyry systems, contact metamorphic skarns, and the enriched zones of copper ore bodies, commonly with chalcopyrite, chalcocite, and other sulfides.

It often develops where primary copper minerals are altered by circulating fluids, and it is a key mineral in the secondary enrichment zones that make many copper deposits economic. Over time, surface weathering can convert bornite to chalcocite and other secondary copper minerals.

Notable localities include Butte in Montana, deposits in Arizona, and many copper districts in Mexico, Peru, and elsewhere.

Bornite is identified by its rich iridescent purple, blue, and red tarnish over a coppery-brown to bronze fresh surface. It is relatively soft (hardness about 3), brittle, and gives a grayish-black streak.

Distinguish genuine bornite from acid-treated chalcopyrite (often sold as peacock ore): natural bornite shows deeper, more uniform purple-blue colors and a brown fresh surface, while treated chalcopyrite has a brassier base. A fresh broken surface revealing bronze-brown metal confirms bornite.

Its softness separates it from harder brassy minerals like pyrite, and its tarnish colors distinguish it from plain chalcopyrite.

Bornite is an important ore of copper, mined along with related sulfides to supply copper for electrical, plumbing, and alloy uses. It can also contain recoverable gold and silver.

Its spectacular iridescence makes it a popular collector mineral and tumbled stone, marketed widely as peacock ore. Buyers should be aware that much commercial peacock ore is treated chalcopyrite rather than true bornite.

Metaphysically, peacock ore is associated with happiness, energy, and renewal, traditions that are cultural rather than scientifically established.