Classification of coal based on volatile matter and cooking power of clean material. Coal is readily combustible rock containing more than 50% by weight of carbonaceous material formed from compaction and indurations of variously altered plant remains similar to those of peat. After a considerable amount of time, heat and burial pressure, it is metamorphosed from peat to lignite. Lignite is considered to be immature coat at this stage of development because it is still somewhat light in color and it remains soft. Lignite increases in maturity by becoming darker and harder and is then classified as sub-bituminous coal. After a continuous process of burial and alteration, chemical and physical changes occur until the coal is classified as bituminous – dark and hard coal. Bituminous coal ignites easily and burns long with a relatively long flame. If improperly fired, bituminous coal is characterized with excess smoke and soot. Anthracite coal is the last classification, the ultimate maturation. Anthracite coal is very hard and shiny