sedimentary

Coal

Anthracite / Bituminous Coal

Hardness: 0.5-2.5 on the Mohs scale. Color: Dark brown to shiny black. Luster: Vitreous to dull or metallic. Structure: Amorphous/non-crystalline organic matrix. Cleavage: Indistinct to conchoidal fracture.

Hardness: 0
Color: Dark brown to shiny black
Luster: Vitreous to dull or metallic

Identified July 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed over millions of years through the decay and compression of ancient plant material (peat) under high temperature and pressure in anoxic swamp environments, predominantly during the Carboniferous period.

Uses & applications

Primarily burned as a fossil fuel for electricity generation, industrial heating, and steel production (coking coal). Smaller amounts are used in carbon filters or artistic carvings.

Geological facts

Coal is an organic sedimentary rock, meaning it consists mostly of carbon along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.

Field identification & locations

Identified by its low density (light weight), black or dark brown color, and soft, smudging texture. Frequently found in historic coal-mining regions, river beds, or along old railroad lines.