Coal, solid, usually brown or black, carbon-rich material that most often occurs in stratified sedimentary deposits. It is one of the most important of the primary fossil fuels.
Coal is 50% by weight carbonaceous matter produced by compaction of organic matter for along time.
Different form of coal is there due to different form of organic matter which the coal is made off.
The discovery of fire made the humans different from other animals. Early fuels were primarily wood, cow dung and straw.