How to identify Peacock Ore (when tarnished)

To correctly identify Peacock Ore (when tarnished) (CuFeS2 (Chalcopyrite) and Cu5FeS4 (Bornite)), 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

   Chalcopyrite: Brassy yellow, often with iridescent tarnish (blue, purple, red). Bornite: Freshly broken, reddish-brown to copper-red; rapidly tarnishes to iridescent blue, purple, and red ('Peacock Ore').

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. Can also form in veins or as coatings.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Chalcopyrite: Tetragonal, often forming pseudotetrahedral or disphenoidal crystals, but commonly massive. Bornite: Orthorhombic (pseudocubic), typically massive, granular, or as disseminated grains. Less commonly forms distinct crystals.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Chalcopyrite: Poor, indistinct {011} cleavage. Bornite: Poor, indistinct {111} cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, porphyry copper deposits, volcanogenic massive sulfide (VMS) deposits, skarn deposits, contact metamorphic deposits, and sedimentary copper deposits.

Key Facts

Hardness

Chalcopyrite: 3.5-4 (Mohs). Bornite: 3 (Mohs).

Specific Gravity

Chalcopyrite: 4.1-4.3. Bornite: 4.9-5.3.

Crystal System

Chalcopyrite: Tetragonal. Bornite: Orthorhombic (pseudocubic).

Color

Chalcopyrite: Brassy yellow, often tarnished. Bornite: Reddish-brown to copper-red, rapidly tarnishing iridescent.

Luster

Metallic.

Transparency

Opaque.

Fracture

Chalcopyrite: Uneven to conchoidal. Bornite: Uneven to subconchoidal.

Cleavage

Chalcopyrite: Poor, indistinct {011}. Bornite: Poor, indistinct {111}.

Composition

Chalcopyrite: Copper iron sulfide (CuFeS2). Bornite: Copper iron sulfide (Cu5FeS4).

Physical characteristics

• Crystal Habit: Chalcopyrite: Commonly massive, disseminated, or in pseudotetrahedral crystals. Bornite: Commonly massive, granular, disseminated, or as exsolution lamellae within chalcopyrite.
• Cleavage Type: Poor/Indistinct.
• Fracture Type: Uneven to subconchoidal.
• Tenacity: Brittle.
• Luster Type: Metallic.

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