mineral
Bornite
Bornite (Cu5FeS4)
Hardness: 3 (Mohs scale); Color: Brownish-bronze turning to iridescent blue-purple-pink (peacock colors) upon tarnishing; Luster: Metallic; Crystal system: Orthorhombic; Specific Gravity: 5.06-5.08.
- Hardness
- 3 (Mohs scale)
- Luster
- Metallic
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Physical properties
Hardness: 3 (Mohs scale); Color: Brownish-bronze turning to iridescent blue-purple-pink (peacock colors) upon tarnishing; Luster: Metallic; Crystal system: Orthorhombic; Specific Gravity: 5.06-5.08.
Formation & geological history
Formed in hydrothermal veins, contact metamorphic zones, and in the enriched zones of copper sulfide deposits. It can be found in igneous and metamorphic rocks.
Uses & applications
A significant ore of copper. High-quality specimens are highly valued by mineral collectors for their vibrant 'peacock' tarnish.
Geological facts
Commonly known as 'Peacock Ore' because of the vivid iridescent tarnish that develops on its surface when exposed to air. Authentic bornite tarnishes naturally, though some commercial pieces sold as 'peacock ore' are actually chalcopyrite treated with acid.
Field identification & locations
Identified by its distinctive metallic iridescent 'oil slick' colors on a dark metallic base. It has a grayish-black streak. Common locations include Montana (USA), Cornwall (UK), and Kazakhstan.
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