Ayers, Walter B. Bureau of Economic Geology, University of Texas, Austin, Texas.
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A brownish-black, low-rank coal defined in the engineering sense by the American Society for Testing and Materials as having a heating value of less than 8300 Btu/lb (4611 kcal/kg), determined on a moist, mineral-matter-free basis. Lignite occurs in two subclasses: lignite A [8300–6300 Btu/lb (4611–3500 kcal/kg)] and lignite B [less than 6300 Btu/lb (3500 kcal/kg)]. Vitrinite reflectance of lignite is 0.25–0.38%; however, vitrinite reflectance may be more suitably applied to higher-rank coals. Outside North America, low-rank coal is classified as brown coal, which includes lignite, subbituminous, and most high-volatile C bituminous coal of the North American classification system. Brown coal is divided into soft and hard coal; hard coal is subdivided into dull and bright coal. See also: Coal
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