mineral

Bornite (Peacock Ore)

Bornite (Cu5FeS4)

Hardness: 3 (Mohs scale); Color: Brownish bronze on fresh surfaces, iridescent purple/blue/green when tarnished; Luster: Metallic; Crystal Structure: Orthorhombic; Cleavage: Poor; Specific Gravity: 5.06-5.08

Hardness: 3 (Mohs scale)
Luster: Metallic

Identified May 9, 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 copper deposits. It is often found in hypogene mineral deposits alongside chalcopyrite.

Uses & applications

Major ore of copper. Specimens are highly popular in the mineral trade and for educational purposes due to their vibrant colors.

Geological facts

Often called 'Peacock Ore' because of its iridescent tarnish. While natural bornite tarnishes over time, many cheap commercial specimens are actually chalcopyrite that has been acid-washed (typically with vinegar or peroxide) to artificially create the colors.

Field identification & locations

Identify in the field by its metallic luster and the characteristic 'oil-on-water' iridescent tarnish. It is much softer than chalcopyrite and will leave a grayish-black streak. Commonly found in copper mining districts like Butte, Montana, or Cornwall, England.