How to identify Bornite

To correctly identify Bornite (Cu5FeS4), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   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.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Metallic.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically massive, granular, or disseminated. Less commonly forms distinct crystals.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   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.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Poor or indistinct cleavage on {111}. More commonly exhibits an uneven to subconchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   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).

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.

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