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Native copper is a naturally occurring metallic element, not combined with other elements in a chemical compound. It is a soft, ductile, and malleable metal with a distinctive reddish-orange color on fresh surfaces, which tarnishes to a dull brown, green, or black upon exposure to air due to the formation of copper oxides and carbonates. It is an excellent conductor of electricity and heat. It often occurs in irregular masses, sheets, wires, dendrites, or distorted crystals.
How to Identify
- Color
- Salmon-pink to reddish-orange on fresh surfaces, tarnishing to dark brown, green (malachite), or black (tenorite) with exposure.
- Luster
- Metallic.
- Texture
- Often irregular masses, wires, sheets, or dendritic growths. Can be massive, arborescent, or granular.
- Crystal Form
- Cubic system, but well-formed crystals are rare. Typically occurs as distorted cubes, octahedra, or dodecahedra. More commonly found as irregular masses, wires (filiform), sheets, or dendritic (tree-like) aggregates.
- Cleavage
- None. Exhibits hackly fracture.
- Geological Environment
- Found in the oxidized zones of copper sulfide deposits, in basaltic lava flows (especially filling amygdules), in conglomerates and sandstones, and in hydrothermal veins. Often associated with zeolites, calcite, epidote, prehnite, and other secondary copper minerals like malachite, azurite, and cuprite.
Key Facts
- Hardness: 2.5-3 on the Mohs scale
- Specific Gravity: 8.9-8.95 g/cm³
- Crystal System: Isometric (Cubic)
- Color: Copper-red, tarnishes to brown, green, or black
- Luster: Metallic
- Transparency: Opaque
- Fracture: Hackly (jagged, sharp-edged)
- Cleavage: None
- Composition: Pure Copper (Cu), often with minor impurities like silver, iron, or bismuth.
Quick Check
- Color: Reddish-orange (fresh) to dark brown/green/black (tarnished)
- Luster: Metallic
- Streak: Copper-red (on unglazed porcelain plate)
Physical Characteristics
- Crystal Habit: Massive, dendritic, arborescent (tree-like), filiform (wire-like), tabular, octahedral, dodecahedral, or distorted cubic crystals.
- Cleavage Type: None
- Fracture Type: Hackly
- Tenacity: Malleable, ductile, sectile
- Luster Type: Metallic
Formation
Native copper forms under reducing conditions, typically in basaltic lava flows, conglomerates, sandstones, and hydrothermal veins. It can precipitate from circulating groundwater or hydrothermal fluids that have leached copper from surrounding rocks. In basaltic environments, it often fills amygdules and fractures. In sedimentary environments, it can replace organic material or cement grains.
Usage
Historically, native copper was one of the first metals used by humans, dating back to the Chalcolithic period (Copper Age) for tools, weapons, and ornaments due to its malleability and ease of working. Today, while most commercial copper is extracted from sulfide and oxide ores, native copper is still valued by collectors and occasionally found in sufficient quantities to be a minor ore. Its primary modern use is as a specimen mineral.
Age Distribution
Native copper deposits can range in age from Precambrian to Cenozoic, with significant occurrences in various geological eras.
Where to Find
Keweenaw Peninsula, Michigan, USA
World-renowned for its vast native copper deposits, primarily found in Precambrian basaltic lava flows and interbedded conglomerates. These deposits were historically mined on a massive scale.
Corocoro, Bolivia
Known for significant native copper occurrences in sedimentary rocks, particularly sandstones and conglomerates.
Bisbee, Arizona, USA
While primarily known for its copper sulfide ores, native copper was also found in the oxidized zones of these deposits.
Broken Hill, New South Wales, Australia
Occurrences of native copper have been reported in association with other copper minerals.
Russia (Urals region)
Various localities have yielded native copper, often in hydrothermal settings.
Finding Tips
Look for Basaltic Environments
In regions with ancient basaltic lava flows, particularly those with amygdaloidal structures (gas bubbles filled with secondary minerals), native copper can be found filling these cavities.
Check Oxidized Zones of Copper Deposits
Native copper can occur in the upper, oxidized portions of copper sulfide ore bodies, where primary sulfides have been altered by weathering processes.
Examine Sedimentary Rocks
In certain sedimentary environments, such as red bed sandstones and conglomerates, native copper can precipitate, often replacing organic material or acting as a cement.
Test for Malleability
Native copper is highly malleable. A small piece can be flattened with a hammer without shattering, which distinguishes it from most other metallic-looking minerals.
Observe Tarnish
The distinctive reddish-orange color on fresh surfaces, and the common green (malachite) or dark tarnish, are good indicators.
Similar Rocks
Cuprite
Cu2O
Also known as: Red Copper Ore
Bornite
Cu5FeS4
Also known as: Peacock Ore
Chalcocite
Cu2S
Also known as: Copper Glance
Chalcopyrite
CuFeS2
Also known as: Copper Pyrites
Gold
Au
Also known as: Aurum
Scientific Classification
- Mineral Class
- Native Elements
- Group
- Copper Group
- Crystal System
- Isometric (Cubic)
- Chemical Formula
- Cu
- Composition
- Copper (Cu) 100%
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