Bornite with Malachite

Mineral Association

Bornite (Cu5FeS4) with Malachite (Cu2(CO3)(OH)2)

Also known as: Peacock Ore (for Bornite), Green Copper (for Malachite)

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Description

Bornite with Malachite refers to a mineral specimen where the primary copper iron sulfide mineral bornite is found in close association with the secondary copper carbonate hydroxide mineral malachite. Bornite is known for its distinctive iridescent tarnish, often displaying shades of blue, purple, red, and green, which gives it the nickname 'peacock ore'. Malachite is characterized by its vibrant green color, often with banding or concentric patterns. This association is common in the upper, oxidized zones of copper ore deposits, where bornite has been altered by circulating groundwater containing dissolved carbon dioxide, leading to the formation of malachite.

How to Identify

Color: Bornite: Fresh surfaces are reddish-brown, quickly tarnishing to iridescent blue, purple, red, and green. Malachite: Bright green to dark green, often banded.
Luster: Bornite: Metallic. Malachite: Silky, vitreous, or dull (earthy).
Texture: Bornite: Granular, massive, or rarely in cubic or dodecahedral crystals. Malachite: Botryoidal, mammillary, stalactitic, fibrous, or massive.
Crystal Form: Bornite: Isometric system, typically massive, granular, or disseminated. Rarely as distorted cubes or dodecahedra. Malachite: Monoclinic system, typically forms botryoidal, mammillary, or stalactitic masses; also fibrous, radiating, or earthy. Rarely as small acicular crystals.
Cleavage: Bornite: Poor to indistinct on {111}. Malachite: Perfect on {001}, good on {100}.
Geological Environment: Oxidized zones of copper sulfide deposits, hydrothermal veins, and contact metamorphic deposits where primary copper sulfides have been altered by weathering processes.

Key Facts

Hardness: Bornite: 3.0-3.25 (Mohs). Malachite: 3.5-4.0 (Mohs).
Specific Gravity: Bornite: 4.9-5.3. Malachite: 3.6-4.0.
Crystal System: Bornite: Isometric. Malachite: Monoclinic.
Color: Bornite: Reddish-brown, tarnishing to iridescent blue, purple, red, green. Malachite: Bright green to dark green.
Luster: Bornite: Metallic. Malachite: Silky, vitreous, dull.
Transparency: Bornite: Opaque. Malachite: Translucent to opaque.
Fracture: Bornite: Uneven to conchoidal. Malachite: Uneven to subconchoidal.
Cleavage: Bornite: Poor to indistinct. Malachite: Perfect on {001}, good on {100}.
Composition: Bornite: Copper iron sulfide (Cu5FeS4). Malachite: Copper carbonate hydroxide (Cu2(CO3)(OH)2).

Quick Check

Color: Bornite: Reddish-brown to iridescent blue/purple/green. Malachite: Bright green.
Luster: Bornite: Metallic. Malachite: Silky, vitreous, or dull.
Streak: Bornite: Grayish-black. Malachite: Light green.

Physical Characteristics

Crystal Habit: Bornite: Massive, granular, disseminated, rarely cubic or dodecahedral crystals. Malachite: Botryoidal, mammillary, stalactitic, fibrous, radiating, massive, rarely acicular crystals.
Cleavage Type: Bornite: Poor/indistinct. Malachite: Perfect in one direction, good in another.
Fracture Type: Bornite: Uneven to conchoidal. Malachite: Uneven to subconchoidal.
Tenacity: Bornite: Brittle. Malachite: Brittle.
Luster Type: Bornite: Metallic. Malachite: Silky, vitreous, dull.

Formation

Bornite is a primary copper iron sulfide mineral that forms in hydrothermal veins, contact metamorphic deposits, and disseminated in igneous rocks. Malachite is a secondary copper carbonate hydroxide mineral that forms in the oxidized zone of copper deposits, often as an alteration product of primary copper sulfides like bornite, chalcopyrite, and chalcocite. The association of bornite with malachite indicates a primary copper sulfide deposit that has undergone subsequent weathering and oxidation.

Usage

Bornite is an important ore of copper. Malachite, while also a minor copper ore, is primarily used as an ornamental stone, pigment, and for jewelry. The combination specimen is valued by collectors for its aesthetic appeal and as an indicator of copper mineralization and subsequent alteration.

Age Distribution

Formed throughout geological history, typically in association with copper deposits of various ages.

Where to Find

Butte, Montana, USA

Historically a major copper mining district, known for rich bornite and other copper sulfide ores, often with secondary malachite.

Cornwall, England

Famous for its copper and tin deposits, where bornite and malachite specimens are found.

Tsumeb, Namibia

A world-renowned locality for diverse and well-crystallized minerals, including excellent bornite and malachite specimens.

Bisbee, Arizona, USA

Another historic copper mining district, producing significant quantities of copper minerals, including bornite and malachite.

Congo (Democratic Republic of Congo)

Known for vast copper deposits, often yielding large and aesthetic malachite specimens, frequently associated with primary copper sulfides like bornite.

Finding Tips

Look for Copper Deposits

Focus your search on areas known for copper mineralization, particularly the oxidized zones of these deposits.

Identify Iridescent Tarnish

Bornite's distinctive iridescent tarnish is a key identifier. Look for metallic minerals with blue, purple, red, and green hues.

Recognize Green Alteration

Malachite's bright green color is unmistakable. It often forms crusts, coatings, or botryoidal masses on or near other copper minerals.

Check for Acid Reaction (Malachite)

Malachite will effervesce (fizz) when a drop of dilute hydrochloric acid is applied, due to its carbonate content. Bornite will not react.

Observe Associated Minerals

Bornite and malachite are often found with other copper minerals like chalcopyrite, chalcocite, azurite, cuprite, and native copper, as well as iron oxides.

Similar Rocks

Chalcopyrite with Malachite

Chalcopyrite (CuFeS2) with Malachite (Cu2(CO3)(OH)2)

Also known as: Copper Pyrites with Malachite

Chalcocite with Malachite

Chalcocite (Cu2S) with Malachite (Cu2(CO3)(OH)2)

Also known as: Copper Glance with Malachite

Azurite with Malachite

Azurite (Cu3(CO3)2(OH)2) with Malachite (Cu2(CO3)(OH)2)

Also known as: Blue Copper with Green Copper

Scientific Classification

Mineral Class: Bornite: Sulfides. Malachite: Carbonates.
Group: Bornite: Sulfide Group. Malachite: Carbonate Group.
Crystal System: Bornite: Isometric. Malachite: Monoclinic.
Chemical Formula: Bornite: Cu5FeS4. Malachite: Cu2(CO3)(OH)2.
Composition: Bornite: Copper (63.3%), Iron (11.1%), Sulfur (25.6%). Malachite: Copper (57.48%), Carbon (5.43%), Hydrogen (0.91%), Oxygen (36.18%).

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