How to identify Calcite with Pyrite

To correctly identify Calcite with Pyrite (CaCO3 (Calcite) with FeS2 (Pyrite)), 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

   Calcite: Typically colorless, white, or light shades (yellow, pink, blue, green, brown, black). Pyrite: Opaque, metallic brass-yellow.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Calcite: Vitreous to sub-vitreous. Pyrite: Metallic.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Calcite: Smooth to slightly rough, depending on crystal habit. Pyrite: Smooth, often with striations on crystal faces.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Calcite: Highly variable, commonly rhombohedral, scalenohedral, prismatic, or tabular. Pyrite: Commonly cubic, pyritohedral, or octahedral; also massive, granular, or radiating.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Calcite: Perfect rhombohedral cleavage in three directions (1011). Pyrite: Indistinct to poor cleavage, conchoidal to uneven fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, sedimentary rocks (especially shales, limestones, and coal seams), metamorphic rocks, and as a gangue mineral in various ore deposits.

Key Facts

Hardness

Calcite: 3 (Mohs). Pyrite: 6-6.5 (Mohs).

Specific Gravity

Calcite: 2.71. Pyrite: 4.95-5.10.

Crystal System

Calcite: Trigonal. Pyrite: Isometric.

Color

Calcite: Colorless, white, various tints. Pyrite: Brassy yellow.

Luster

Calcite: Vitreous to sub-vitreous. Pyrite: Metallic.

Transparency

Calcite: Transparent to translucent. Pyrite: Opaque.

Fracture

Calcite: Conchoidal to uneven. Pyrite: Conchoidal to uneven.

Cleavage

Calcite: Perfect rhombohedral (3 directions at 74°55'). Pyrite: Indistinct to poor.

Composition

Calcite: Calcium Carbonate (CaCO3). Pyrite: Iron Disulfide (FeS2).

Physical characteristics

• Crystal Habit: Calcite: Rhombohedral, scalenohedral, prismatic, tabular, massive, granular. Pyrite: Cubic, pyritohedral, octahedral, massive, granular, radiating.
• Cleavage Type: Calcite: Perfect rhombohedral. Pyrite: Indistinct/poor.
• Fracture Type: Calcite: Conchoidal to uneven. Pyrite: Conchoidal to uneven.
• Tenacity: Calcite: Brittle. Pyrite: Brittle.
• Luster Type: Calcite: Vitreous. Pyrite: Metallic.

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