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Earth and Space Sciences · Glossary

What is Coal; coalification; rank?

Also known as: coal · coalification · rank (of coal)

Definition 18.11 High School Earth and Space Sciences · Chapter 18 — The Geology of Coal, Oil and Gas

Coal is a sedimentary rock made mostly of the remains of land plants, rich in carbon. Coalification is the transformation of peat into coal and of coal into richer coal, by burial and heating. The rank of a coal is how far coalification has gone: from lignite through subbituminous and bituminous coal to anthracite, the carbon content rises.

Top left: carbon content of the ranks of coal. Data: U.S. Energy Information Administration. Top right: a bed of lignite, the black band under pale sands, exposed in a mine in Romania; photograph U.S. Geological Survey (public domain). Bottom, from left: lignite, about 4.5\, cm across, brown-black and dull; bituminous coal, with flattened plant fragments; anthracite, black and glassy. Photographs James St. John (CC BY 2.0). Top left: carbon content of the ranks of coal. Data: U.S. Energy Information Administration. Top right: a bed of lignite, the black band under pale sands, exposed in a mine in Romania; photograph U.S. Geological Survey (public domain). Bottom, from left: lignite, about 4.5\, cm across, brown-black and dull; bituminous coal, with flattened plant fragments; anthracite, black and glassy. Photographs James St. John (CC BY 2.0). Top left: carbon content of the ranks of coal. Data: U.S. Energy Information Administration. Top right: a bed of lignite, the black band under pale sands, exposed in a mine in Romania; photograph U.S. Geological Survey (public domain). Bottom, from left: lignite, about 4.5\, cm across, brown-black and dull; bituminous coal, with flattened plant fragments; anthracite, black and glassy. Photographs James St. John (CC BY 2.0). Top left: carbon content of the ranks of coal. Data: U.S. Energy Information Administration. Top right: a bed of lignite, the black band under pale sands, exposed in a mine in Romania; photograph U.S. Geological Survey (public domain). Bottom, from left: lignite, about 4.5\, cm across, brown-black and dull; bituminous coal, with flattened plant fragments; anthracite, black and glassy. Photographs James St. John (CC BY 2.0).
Top left: carbon content of the ranks of coal. Data: U.S. Energy Information Administration. Top right: a bed of lignite, the black band under pale sands, exposed in a mine in Romania; photograph U.S. Geological Survey (public domain). Bottom, from left: lignite, about 4.5 cm4.5\,\mathrm{cm} across, brown-black and dull; bituminous coal, with flattened plant fragments; anthracite, black and glassy. Photographs James St. John (CC BY 2.0).
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