Lignite

Lignite, variety of coal, also known as brown 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 colour and often shows a distinct fibrous or woody structure. Lignite is inferior in calorific value to ordinary coal because of its high (30-75 per cent) water content and low (60-68 per cent) carbon content; the high (52.5-62.5 per cent) content of volatile matter causes lignite to disintegrate rapidly on exposure to air. The heat value of lignite is 7,807 kJ (7,400 BTU) per lb.