Overview:

Coal is our most abundant fossil fuel resource. Coal is a complex mixture of organic chemical substances containing carbon, hydrogen and oxygen in chemical combination, together with smaller amounts of nitrogen and sulfur. This organic part of coal has associated with it various amounts of moisture and minerals.

Coalification is the name given to the development of the series of substances known as peat, lignite or brown coal, sub-bituminous coal, bituminous coal, and anthracite. The degree of coalification, also called the rank of the coal, increases progressively from lignite to low rank coal, to high rank coal, to anthracite. The carbon content increases, while the oxygen and hydrogen contents decrease throughout the series. The hardness increases, while the reactivity decreases. Different amounts of heat and pressure during the geochemical stage of coal development cause these differences in rank. It is not due to the kind of plants the coal is formed from.

Coals in the US range from lignite with approximate as-mined carbon content of 30%, volatile matter 27%, and heating value of 7,000 Btu per pound, to anthracite with an average of 85% carbon, 5% volatile matter, and heating value of 12,750 Btu per pound. Sub-bituminous and bituminous coals are intermediate between these values.

Use the underlined links above to go to tutorials and pages of links for various aspects of coal.