mineral

Bornite (Peacock Ore)

Bornite (Cu5FeS4)

Hardness: 3 on Mohs scale; Color: Copper-red to brown on fresh surfaces, tarnishing to iridescent shades of blue, purple, and green; Luster: Metallic; Crystal Structure: Orthorhombic (pseudocubic); Cleavage: Poor; Specific Gravity: 5.06-5.08

Hardness: 3 on Mohs scale
Luster: Metallic

Identified March 24, 2026More mineral →

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Physical properties

Formation & geological history

Formed in hydrothermal veins, contact metamorphic zones, and as a secondary mineral in enriched zones of copper sulfide deposits. It can occur in deposits spanning various geological ages from Precambrian to recent.

Uses & applications

A major ore of copper (containing about 63% copper by mass). High-quality iridescent specimens are popular in mineral collecting and as decorative curiosities.

Geological facts

Known as 'Peacock Ore' due to its vibrant iridescent tarnish. While natural bornite tarnishes over time, many specimens sold in shops are actually chalcopyrite that has been acid-washed (typically with vinegar or peroxide) to artificially induce the colorful 'peacock' effect.

Field identification & locations

Identify by its 'oil-slick' iridescence and grey-black streak. It is commonly found in copper-rich areas like Butte, Montana (USA), Cornwall (UK), and various mines in Mexico and Chile. In the field, look for metallic mass in association with other copper minerals like chalcopyrite or chalcocite.