Lignite

Lignite, variety of coal, intermediate in quality between peat and bituminous coal. Geologically, lignite is of comparatively recent origin, occurring in Cretaceous and Tertiary strata. It is usually brownish-black in color and often shows a distinct fibrous or woody structure. Lignite is inferior in calorific value to ordinary coal because of its high (30-75 percent) water content and low (60-68 percent) carbon content; the high (52.5-62.5 percent) content of volatile matter causes lignite to disintegrate rapidly on exposure to air. The heat value of lignite is 7807 kJ (7400 Btu) per lb. See Coal.