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Coal is a readily combustible rock containing more than 50 percent organic matter (carbon) by weight, and 70 percent carbonaceous material by volume including inherent moisture, which was formed from the compaction and alteration of plant remains.

Schopf (1956, 1966); Jackson (1997); Alpern and DeSousa (2002)

Similarly, the American Society for Testing and Materials (ASTM International) recognizes coal as having less than 25 weight percent ash (on a dry basis), and impure coal as having greater than or equal to 25 weight percent, but less than 50 weight percent ash (on a dry basis). Ash is the noncombustible material in coal. If a coal has more than 50 percent ash, it would be a carbonaceous shale, rather than coal.

Facts about coal

  • Coal is a rock that can burn.
  • Coal is an energy source.
  • Coal is a sedimentary rock.
  • Coal is an energy mineral (legally a mineral, scientifically a rock).
  • Coal is fossil fuel (because it is derived from fossil plant remains).
  • Coal is a solid hydrocarbon (because it consists mostly of carbon, hydrogen, and oxygen; in contrast, oil is a liquid hydrocarbon, and natural gas is a gaseous hydrocarbon).
  • Coal and the peat it comes from are part of the carbon cycle.

Kentucky Energy & Envioronment Cabinet

These pages partly funded by grants from Office of Energy Policy.



Last Modified on 2023-01-05
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