How to identify Calcite with Pyrite

To correctly identify Calcite with Pyrite (CaCO3 with FeS2), 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 white, colorless, grey, yellow, pink, or brown. Pyrite: Pale brass-yellow, metallic.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Calcite: Vitreous to pearly. Pyrite: Metallic.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Calcite: Crystalline, granular, massive. Pyrite: Crystalline (often euhedral cubes, octahedra), massive, granular.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Calcite: Rhombohedral, scalenohedral, prismatic, tabular. Pyrite: Cubic, octahedral, pyritohedral, massive.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Calcite: Perfect rhombohedral (3 directions at 74° and 106°). Pyrite: Indistinct to poor, conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, sedimentary rocks (especially shales, limestones), 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, grey, yellow, pink, brown; Pyrite: Pale brass-yellow.

Luster

Calcite: Vitreous to pearly; Pyrite: Metallic.

Transparency

Calcite: Transparent to translucent; Pyrite: Opaque.

Fracture

Calcite: Conchoidal to uneven; Pyrite: Uneven to conchoidal.

Cleavage

Calcite: Perfect rhombohedral (3 directions); Pyrite: Indistinct to poor.

Composition

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

Physical characteristics

• Crystal Habit: Calcite: Rhombohedral, scalenohedral, prismatic, massive, granular; Pyrite: Cubic, octahedral, pyritohedral, massive, granular, radiating.
• Cleavage Type: Calcite: Perfect rhombohedral {1011}; Pyrite: Indistinct {001} or poor.
• Fracture Type: Calcite: Conchoidal to uneven; Pyrite: Uneven to conchoidal.
• Tenacity: Calcite: Brittle; Pyrite: Brittle.
• Luster Type: Calcite: Vitreous to pearly; Pyrite: Metallic.

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