Coal is made out of residue of trees and plants from millions of years ago through combined effects of pressure and heat. It is a sedimentary, organic and combustible rock composed mainly of carbon, oxygen and hydrogen.
Coal is more plentiful than oil or natural gas and is mainly used to produce electricity and heat through combustion. It is also an essential material for cement, steel and other industrial products and is important in the production of a wide range of chemical fertilizers and other chemical-related products. It is extracted underground by shaft mining, or at ground level by open-pit-mining extraction.