mineral

Bornite (Peacock Ore)

Bornite (Cu5FeS4)

Hardness: 3-3.25; Color: Brownish-bronze but tarnishes to iridescent blue/purple/green; Luster: Metallic; Crystal Structure: Orthorhombic; Cleavage: Poor; Specific Gravity: 5.06-5.08

Hardness: 3-3
Luster: Metallic

Identified May 17, 2026More mineral →

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Physical properties

Hardness: 3-3.25; Color: Brownish-bronze but tarnishes to iridescent blue/purple/green; Luster: Metallic; Crystal Structure: Orthorhombic; Cleavage: Poor; Specific Gravity: 5.06-5.08

Formation & geological history

Forms primarily in hydrothermal veins and as a primary or secondary copper mineral in porphyry copper deposits. It can occur in magmatic and metamorphic rocks as well.

Uses & applications

Important ore of copper; highly popular as a decorative display mineral for collectors due to its vibrant iridescent colors.

Geological facts

Often called 'Peacock Ore' because of its brilliant iridescent tarnish. While original surfaces are bronze, exposure to air causes the signature rainbow effect. Chalcopyrite is often acid-treated to mimic this look for tourists.

Field identification & locations

Identify in the field by its metallic luster and the presence of brilliant blue or purple tarnish on an otherwise brownish-metallic base. Found in copper-rich mining districts like Butte, Montana or Cornwall, England.