sedimentary

Coal

Carbonaceous sedimentary rock (C)

Hardness: 0.5-2.5 on Mohs scale; Color: Black to brownish-black; Luster: Dull to sub-metallic; Structure: Amorphous/Non-crystalline; Cleavage: None/Conchoidal fracture; Specific Gravity: 1.1-1.5

Hardness: 0
Color: Black to brownish-black
Luster: Dull to sub-metallic

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 0.5-2.5 on Mohs scale; Color: Black to brownish-black; Luster: Dull to sub-metallic; Structure: Amorphous/Non-crystalline; Cleavage: None/Conchoidal fracture; Specific Gravity: 1.1-1.5

Formation & geological history

Formed from the accumulation and burial of plant remains in swampy environments. Over millions of years (primarily Carboniferous period), heat and pressure transform peat into lignite, sub-bituminous, bituminous, and eventually anthracite coal.

Uses & applications

Primarily used as a combustible fuel for electricity generation, steel production (coke), and various industrial heating processes.

Geological facts

Coal is often referred to as 'buried sunshine' because it stores solar energy captured by plants millions of years ago. It is the largest source of energy for the generation of electricity worldwide.

Field identification & locations

Identify by its black streak, lightweight feel compared to most rocks, and tendency to be brittle or crumbly. It is common in areas with ancient inland seas or prehistoric peat bogs.