sedimentary
Likely bituminous coal
Coal, predominantly carbon-rich organic matter; exact rank cannot be confirmed from the image
AI-generated identification · may be incorrectDark gray to black, irregular and somewhat lustrous surface; coal is generally brittle and lacks a regular crystal structure. Hardness and density vary by coal rank; the specimen’s properties cannot be measured visually.
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Physical properties
Dark gray to black, irregular and somewhat lustrous surface; coal is generally brittle and lacks a regular crystal structure. Hardness and density vary by coal rank; the specimen’s properties cannot be measured visually.
Formation & geological history
Forms when buried plant material is compacted and altered by heat and pressure over geologic time, commonly in ancient swamp deposits. The image does not reveal its age or provenance.
Uses & applications
Coal is used chiefly as fuel and, when suitable, to make coke for steelmaking; this small piece may be a teaching or collector specimen.
Geological facts
Coal is an organic sedimentary rock, unlike most rocks that consist mainly of mineral grains.
Field identification & locations
Its black color, low density, brittleness, and possible black streak can help identify it; distinguish it from black minerals by testing streak and hardness. Coal deposits occur worldwide, including major basins in China, the United States, India, Australia, and Europe.
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