sedimentary
Coal (likely Bituminous or Lignite)
Organic Sedimentary Rock (Carbonaceous)
Hardness: 1-2.5 on Mohs scale; Color: Black to dark brown; Luster: Dull to sub-vitreous; Structure: Amorphous/Organic; Cleavage: None (conchoidal fracture); Specific Gravity: 1.1–1.5
- Hardness
- 1-2
- Color
- Black to dark brown
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 1-2.5 on Mohs scale; Color: Black to dark brown; Luster: Dull to sub-vitreous; Structure: Amorphous/Organic; Cleavage: None (conchoidal fracture); Specific Gravity: 1.1–1.5
Formation & geological history
Formed from the remains of prehistoric vegetation (peats) buried under high pressure and heat over millions of years, primarily during the Carboniferous period.
Uses & applications
Primarily used as a fuel source for electricity generation and industrial steel production (coke). Collector value is mostly for educational or historical purposes.
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 electricity generation worldwide.
Field identification & locations
Identify by its light weight compared to stone, black streak when rubbed on ceramic, and its tendency to be brittle and soil hands with black dust. Common in basin regions with sedimentary layers.
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