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What Is Coal?
Coal is a combustible sedimentary rock composed mostly of carbon and hydrocarbons. The energy in coal comes from the energy stored by plants that lived hundreds of millions of years ago in swampy forests. Over time, layers of dead plants at the bottom of the swamps were covered by layers of water and dirt, trapping the energy of the dead plants. The heat and pressure from the top layers turned the plant remains into coal. Coal is a plentiful resource that has been used for thousands of years to produce energy, both in the form of heat and electricity.



Types of Coal:
Coal is a complex resource and can vary in composition even within the same deposit. Generally, there are four different types or ranking levels of coal, each with differences in energy output as a result of increased pressurization, heat, and time.

Lignite This is a brownish-black coal with high moisture and ash content, which has the lowest heating value of the four types of coal. It is considered an immature coal that is still soft. It is used for generating electricity.

Subbituminous coal This is a dull black coal with a higher heating value than lignite, and is used principally for electricity and space heating.

Bituminous coal It is a dark, hard coal that has a higher heating value than lignite and subbituminous coal, but a lower heating value than anthracite.

Anthracite This is also known as "hard coal" that was formed from bituminous coal under increased pressures in rock strata during the creation of mountain ranges. It is very hard and shiny. This type of coal is the most compact and therefore, has the highest energy content of the four levels of coal. It is used for space heating and generating electricity.



What Is Coal Used For?
Coal is used primarily as an energy source, either for heat or electricity. It was once heavily used to heat homes and power locomotives and factories. Bituminous coal is also used to produce coke for making steel and other industrial process heating. Coal gasification and coal liquefaction (coal-to-liquids) are also possible uses of coal for producing synthetic fuel.