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.