Coal

Coal is a fossil fuel and is the altered remains of prehistoric vegetation that originally accumulated in swamps and peat bogs, it is a black or brown rock that can be ignited and burned to produce energy in the form of heat. Coal\'s chemical makeup is a complex mix of elements that include sulphur, carbon, oxygen, hydrogen and nitrogen, as well as small quantities of aluminium, zirconium and many other minerals. Some water is always present.

The energy we get from coal today comes from the energy that plants absorbed from the sun millions of years ago. All living plants store solar energy through a process known as photosynthesis. When plants die, this energy is usually released as the plants decay. Under conditions favourable to coal formation, the decaying process is interrupted, preventing the release of the stored solar energy. The energy is locked into the coal.

Coal is classified by rank, which is a measure of the amount of alteration it has undergone during formation. Consecutive stages in evolution of rank, from an initial peat stage, are brown coal (or lignite), sub-bituminous coal, bituminous coal, and anthracite. Increase in rank is due to a gradual increase in temperature and pressure that results in a decrease in water content and therefore an increase in carbon content. A continuous gradation occurs between these ranks. Sub-bituminous coal, bituminous coal and anthracite are together known as black coal.

The Industrial Revolution that began in Britain in the early 19th century was fuelled by coal. Then, in the 1950s and 1960s, it was eclipsed by petroleum as the world\'s most used fuel, but the oil shocks of the 1970s resulted in a worldwide resurgence of interest in coal as an energy source because of its relative abundance.