Bornite (Peacock Ore)

Physical Properties

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

Formation & Geological History

Formed primarily in hydrothermal veins, contact metamorphic zones, and as a secondary mineral in enriched copper deposits. It occurs in igneous rocks as well as pegmatites.

Uses & Applications

Bornite is a significant ore of copper. In its iridescent form, it is highly popular as a decorative 'pocket stone' and a beginner-level collectible specimen. It is not typically used in jewelry due to its relative softness.

Geological Facts

Commonly known as 'Peacock Ore' because of its brilliant iridescent tarnish. While Bornite naturally tarnishes, many specimens sold in shops are actually Chalcopyrite that has been acid-treated to enhance the rainbow effect.

Field Identification & Locations

Identify in the field by its characteristic purple/blue tarnish which can be scratched away to reveal a bronze-colored interior. It is commonly found in copper mines in locations like Arizona (USA), Mexico, Peru, and Chile.

Identified on: 4/17/2026

Mode: Standard