Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Bornite is a copper iron sulfide mineral with the chemical formula Cu5FeS4. It is well-known for its distinctive iridescent tarnish, which develops upon exposure to air, displaying shades of blue, purple, red, and green, resembling a peacock's feathers. This tarnish is a thin film of oxidation products on the surface. Freshly broken bornite is typically a reddish-brown to copper-red color. The term "Peacock Ore" often refers to bornite that has naturally tarnished or, more commonly, chalcopyrite that has been acid-treated to induce a similar iridescent tarnish for commercial purposes. It is crucial to distinguish between naturally tarnished bornite and treated chalcopyrite when purchasing "Peacock Ore."
How to Identify
- Color
- Freshly broken surfaces are reddish-brown to copper-red. Upon exposure to air, it rapidly tarnishes to iridescent shades of blue, purple, red, and green.
- Luster
- Metallic.
- Texture
- Typically massive, granular, or disseminated. Crystals are rare but can be cubic, dodecahedral, or octahedral.
- Crystal Form
- Cubic system. Crystals are typically pseudocubic, dodecahedral, or octahedral, but often found as massive aggregates or disseminated grains.
- Cleavage
- Poor or indistinct on {111}.
- Geological Environment
- Hydrothermal veins, contact metamorphic deposits, disseminated in mafic igneous rocks, and in the supergene enrichment zones of copper sulfide deposits.
Key Facts
- Hardness: 3 on the Mohs scale.
- Specific Gravity: 4.9-5.3 g/cm³.
- Crystal System: Isometric (Cubic).
- Color: Reddish-brown to copper-red, tarnishing to iridescent blue, purple, red, green.
- Luster: Metallic.
- Transparency: Opaque.
- Fracture: Conchoidal to uneven.
- Cleavage: Poor/indistinct on {111}.
- Composition: Copper iron sulfide (Cu5FeS4).
Quick Check
- Color: Reddish-brown to copper-red on fresh surfaces, rapidly tarnishing to iridescent blue, purple, red, and green.
- Luster: Metallic.
- Streak: Grayish-black.
Physical Characteristics
- Crystal Habit: Typically massive, granular, or disseminated. Rarely as pseudocubic, dodecahedral, or octahedral crystals.
- Cleavage Type: Poor to indistinct, typically not observed in hand samples.
- Fracture Type: Conchoidal to uneven.
- Tenacity: Brittle.
- Luster Type: Metallic.
Formation
Bornite typically forms in hydrothermal veins, contact metamorphic deposits, and disseminated in igneous and metamorphic rocks. It is a primary copper ore mineral, often associated with chalcopyrite, pyrite, and other sulfide minerals. It can also form as a secondary mineral in the supergene enrichment zones of copper deposits.
Usage
Bornite is a significant ore of copper. Its attractive iridescent tarnish makes it popular as an ornamental stone, often sold as "Peacock Ore" for decorative purposes, lapidary work, and in the metaphysical market. It is also a collector's mineral.
Age Distribution
Bornite forms in various geological settings and is not restricted to a specific geological age. It is found in deposits ranging from Precambrian to Cenozoic.
Where to Find
Butte, Montana, USA
Historically a major source of copper, with significant bornite occurrences.
Cornwall, England
Known for various copper minerals, including bornite.
Mexico
Several copper deposits throughout Mexico contain bornite.
Chile
A world leader in copper production, with bornite found in many large porphyry copper deposits.
Peru
Another significant copper-producing country with bornite occurrences.
Zambia and Democratic Republic of Congo
Part of the African Copperbelt, rich in copper sulfide minerals including bornite.
Finding Tips
Look for Copper Deposits
Bornite is a copper ore, so search in areas known for copper mineralization, particularly in sulfide-rich environments.
Examine Freshly Broken Surfaces
While the iridescent tarnish is characteristic, a fresh break will reveal the true reddish-brown to copper-red color, which helps differentiate it from other tarnished sulfides.
Check for Associated Minerals
Bornite often occurs with other sulfide minerals like chalcopyrite, pyrite, chalcocite, and covellite, as well as quartz and calcite.
Be Aware of Treated Chalcopyrite
Much of the 'Peacock Ore' sold commercially is acid-treated chalcopyrite. Naturally tarnished bornite will have a more stable and often deeper iridescence, while treated chalcopyrite may have a brighter, more superficial tarnish that can sometimes rub off or fade.
Similar Rocks
Chalcopyrite
Chalcopyrite
Also known as: Copper Pyrites, Yellow Copper Ore
Covellite
Covellite
Also known as: Indigo Copper
Pyrite
Pyrite
Also known as: Fool's Gold
Scientific Classification
- Mineral Class
- Sulfides
- Group
- Sulfide Minerals
- Crystal System
- Isometric (Cubic)
- Chemical Formula
- Cu5FeS4
- Composition
- Copper (Cu) 63.33%, Iron (Fe) 11.16%, Sulfur (S) 25.51% by weight.
Explore Peacock Ore
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.