mineral
Bornite (Peacock Ore)
Bornite (Cu5FeS4)
Hardness: 3 on Mohs scale; Color: Iridescent blue, purple, and green tarnish over a bronze-brown interior; Luster: Metallic; Crystal Structure: Orthorhombic (often massive); Cleavage: Poor; Specific Gravity: 5.06-5.08
- Hardness
- 3 on Mohs scale
- Luster
- Metallic
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Physical properties
Hardness: 3 on Mohs scale; Color: Iridescent blue, purple, and green tarnish over a bronze-brown interior; Luster: Metallic; Crystal Structure: Orthorhombic (often massive); Cleavage: Poor; Specific Gravity: 5.06-5.08
Formation & geological history
Found in copper deposits, hydrothermal veins, and contact metamorphic zones. It forms through the crystallization of copper-rich hydrothermal fluids.
Uses & applications
Major ore of copper; highly popular as a decorative specimen for collectors due to its vibrant colors.
Geological facts
While bornite naturally tarnishes to iridescent colors, many retail specimens labeled 'Peacock Ore' are actually chalcopyrite that has been acid-washed to artificially induce a bright blue and purple patina.
Field identification & locations
Identified by its intense blue/purple metallic tarnish and its relatively soft nature compared to other metallic sulfides. Commonly found in Butte, Montana, and copper mines in Mexico and Chile.
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