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 renowned for its distinctive iridescent tarnish, which develops upon exposure to air, displaying shades of blue, purple, red, and green, hence its common name "peacock ore." When freshly broken, bornite has a reddish-brown to copper-red color. It is an important ore mineral for copper and is often found in association with other copper sulfides like chalcopyrite, chalcocite, and covellite.
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. Less commonly forms distinct crystals.
- Crystal Form
- Cubic system, but well-formed crystals are rare. When present, they are usually dodecahedral, octahedral, or cubic. More commonly found as massive aggregates or disseminated grains.
- Cleavage
- Poor or indistinct cleavage on {111}. More commonly exhibits an uneven to subconchoidal fracture.
- Geological Environment
- Hydrothermal veins, porphyry copper deposits, skarns, sedimentary copper deposits, and supergene enrichment zones.
Key Facts
- Hardness: 3 on the Mohs scale.
- Specific Gravity: 4.9-5.3.
- Crystal System: Cubic (isometric).
- Color: Reddish-brown to copper-red (fresh); iridescent blue, purple, green, red (tarnished).
- Luster: Metallic.
- Transparency: Opaque.
- Fracture: Uneven to subconchoidal.
- Cleavage: Poor or indistinct on {111}.
- Composition: Copper iron sulfide (Cu5FeS4).
Quick Check
- Color: Reddish-brown to copper-red when fresh, rapidly tarnishing to iridescent blue, purple, green, and red.
- Luster: Metallic.
- Streak: Grayish-black.
Physical Characteristics
- Crystal Habit: Typically massive, granular, or disseminated. Rarely forms distinct cubic, dodecahedral, or octahedral crystals.
- Cleavage Type: Poor/indistinct {111}.
- Fracture Type: Uneven to subconchoidal.
- Tenacity: Brittle.
- Luster Type: Metallic.
Formation
Bornite forms in a variety of geological environments, primarily as a primary mineral in hypogene copper deposits (magmatic-hydrothermal systems, porphyry copper deposits, and skarns) and as a secondary mineral in supergene enrichment zones. It can also occur in sedimentary copper deposits (e.g., Kupferschiefer-type) and in some metamorphic rocks. Its formation is favored by moderate to high temperatures (typically 200-500 C) and sulfur-rich, reducing conditions.
Usage
Bornite is a significant ore mineral of copper, although chalcopyrite (CuFeS2) is generally more abundant. It is mined for its copper content, which is extracted through various beneficiation processes, including flotation. It is also occasionally used as an ornamental stone due to its iridescent tarnish, often sold as "peacock ore."
Age Distribution
Found in various geological ages, typically associated with copper mineralization events.
Where to Find
Butte, Montana, USA
Historically a major copper mining district, known for significant bornite occurrences.
Cornwall, England
Famous for its copper and tin deposits, where bornite is found.
Mexico
Various copper deposits throughout Mexico contain bornite.
Chile
Large porphyry copper deposits, such as Chuquicamata, host substantial bornite mineralization.
Peru
Another major copper-producing country with bornite occurrences in its extensive mineral deposits.
Zambia and Democratic Republic of Congo
Part of the 'Copperbelt' region, known for its stratiform copper deposits where bornite is common.
Finding Tips
Look for Iridescence
The most striking characteristic of bornite is its iridescent tarnish. Look for rocks with patches of blue, purple, green, and red on a metallic surface.
Associated Minerals
Bornite often occurs with other copper sulfides like chalcopyrite, chalcocite, and covellite, as well as pyrite and quartz. Identifying these associated minerals can help confirm bornite's presence.
Fresh Break
If possible, observe a freshly broken surface to see the characteristic reddish-brown to copper-red color before it tarnishes.
Specific Gravity Test
Bornite is relatively dense (specific gravity 4.9-5.3). If you have a sample, its weight can be a clue.
Geological Context
Focus your search in areas known for copper mineralization, such as old mine dumps, hydrothermal alteration zones, or areas with exposed sulfide-rich rocks.
Similar Rocks
Chalcopyrite
Chalcopyrite (CuFeS2)
Also known as: Copper Pyrites
Chalcocite
Chalcocite (Cu2S)
Also known as: Copper Glance
Covellite
Covellite (CuS)
Also known as: Indigo Copper
Pyrite
Pyrite (FeS2)
Also known as: Fool's Gold
Scientific Classification
- Mineral Class
- Sulfides
- Group
- Bornite Group
- Crystal System
- Cubic (Isometric)
- Chemical Formula
- Cu5FeS4
- Composition
- Copper (Cu) 63.33%, Iron (Fe) 11.11%, Sulfur (S) 25.56% (by weight)
Explore Bornite
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.