coal

The formation of coal. Coal forms where vegetable matter accumulates but is prevented from complete decay and forms peat beds. Over time it becomes buried and compressed, forming lignite. Increased pressure and temperature produces bituminous coal with a higher carbon content. At great depths, high temperatures reduce methane and anthracite is formed with a very high carbon concentration.

Black or blackish mineral substance formed from the compaction of ancient plant matter in tropical swamp conditions. It is used as a fuel and in the chemical industry. Coal is classified according to the proportion of carbon it contains. The main types are anthracite (shiny, with about 90% carbon), bituminous coal (shiny and dull patches, about 75% carbon), and lignite (woody, grading into peat, about 50% carbon). Coal can be burned to produce heat energy, for example in power stations to produce electricity. Coal burning is one of the main causes of acid rain, which damages buildings and can be detrimental to aquatic and plant life.

In the second half of the 18th century, coal became the basis of the Industrial Revolution. Coal fields are widely distributed throughout the temperate northern hemisphere, the greatest reserves being in Europe, western Siberia, and the USA. In the Southern hemisphere, Australia is a major producer. An increasing use, from 1950–70, of cheap natural gas and oil as fuel and for the production of electricity halted when the energy crisis of the 1970s led to greater exploitation of coal resources. Coal is becoming a major source of synfuel (synthetic petrol). In the Fischer–Tropsch process (used in Germany in World War II and today in South Africa), the coal is gasified and then catalysts are used to reconstitute it into diesel and jet fuel. In the degradation process (under development in the USA for high-octane motor fuel), a liquid fuel is directly produced by adding hydrogen or removing carbon from the coal.