U.S. Department of Energy


Date of this Version



Ann. Rev. Energy. 1984. 9: 473-99


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Low-rank coals-lignite and subbituminous coal-are those that have been subjected to the least metamorphic change during the coal-forming process. As such, they retain greater fractions of moisture and volatile matter and contain less fixed carbon than the high-rank coals-bituminous and anthracite. The primary measure used to classify the lower ranks of coal is the heating value. Lignite is defined by the American Society for Testing and Materials (standard D-388) as coal with a heating value less than 8300 Btujlb, on a moist, mineral-matter-free basis (m,mmf). Subbituminous coal ranges in heating value from 8300 to 11,500 Btujlb (m,mmf). Bituminous coal and anthracite range from 10,500 to over 15,000 Btu/lb (m,mmf).