How to identify Coal with Pyrite

To correctly identify Coal with Pyrite (Bituminous Coal with Pyrite (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

   Coal is typically black to dark brownish-black. Pyrite is brassy yellow, pale gold, or silvery-yellow.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Coal can range from vitreous (glassy) to dull or earthy. Pyrite has a distinct metallic luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Coal is generally brittle, often with a blocky or layered texture. Pyrite is hard and can be granular, massive, or crystalline.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Coal does not have a crystal form. Pyrite commonly forms cubes, octahedra, or pyritohedra, or can be massive or granular.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Coal exhibits no true cleavage but has a fracture pattern. Pyrite has indistinct cleavage on {100} and {110}.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in sedimentary basins where ancient peat swamps were buried and coalified. Pyrite forms within these coal seams, often indicating marine or brackish water influence during peat deposition or later diagenetic processes.

Key Facts

Hardness

Coal: 2.5-3 (Mohs); Pyrite: 6-6.5 (Mohs)

Specific Gravity

Coal: 1.2-1.5 g/cm³; Pyrite: 5.0-5.2 g/cm³

Crystal System

Coal: Amorphous; Pyrite: Isometric

Color

Black (coal); Brassy yellow, pale gold (pyrite)

Luster

Vitreous to dull/earthy (coal); Metallic (pyrite)

Transparency

Opaque

Fracture

Conchoidal to irregular (coal); Uneven to conchoidal (pyrite)

Cleavage

None (coal); Indistinct on {100} and {110} (pyrite)

Composition

Coal: Primarily carbon (75-90% by weight) with varying amounts of hydrogen, oxygen, nitrogen, and sulfur; Pyrite: Iron disulfide (FeS2), 46.55% Fe, 53.45% S

Physical characteristics

• Crystal Habit: Coal: Massive, banded; Pyrite: Cubes, octahedra, pyritohedra, massive, granular, framboidal
• Cleavage Type: Coal: None; Pyrite: Indistinct
• Fracture Type: Coal: Conchoidal to irregular; Pyrite: Uneven to conchoidal
• Tenacity: Coal: Brittle; Pyrite: Brittle
• Luster Type: Coal: Vitreous to dull/earthy; Pyrite: Metallic

Explore Coal with Pyrite