Along with oil and gas, coal is a fossil fuel. It is a rock that was formed from the remains of living things that died millions of years ago and are preserved as fossils. Coal was first mined as a fuel on an industrial scale in the 18th century, when it was used in furnaces to power steam engines and smelt iron. Today it is used in power stations to produce electricity. Coke, a baked form of coal, is a smokeless fuel used in making iron and steel.

Formation of coal

Coal began to form about 350 million years ago. Then, parts of the Earth’s surface were covered with swamps where trees and giant ferns grew. When these plants died, they rotted down and gradually changed into a dark soil called peat (1).

As the centuries passed, the peat was buried under layers of sand and mud (2). Successive layers pressed down more and more tightly until the peat was compressed into layers of hard, black, shiny rock: coal (3). Folding and faulting of rock layers, the result of Earth movements over millions of years have brought some coal layers close to the surface (4).
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Mining

Today much of the world’s coal is buried under layers of rock. It can be reached only by underground mining. The coal is found in layers called seams. First, geologists locate the coal by studying rock formations in the Earth’s crust. Then the mining company drills vertical shafts down to the level of the coal. A network of tunnels leads from the bottom of the shafts to the coal face. Miners are taken down the shafts in lifts. They mine the coal using powerful, electric, coal-cutting excavating machines. The coal is brought to the surface in large containers.

Modern technology has allowed coal mines to become much safer, largely avoiding the need for men to be working in dangerous conditions deep underground. Many coal mines today use a large, remote-controlled, rotating steel drum, called a continuous mining machine. The coal is scraped from the seam with the machine's tungsten carbide teeth. The loosened coal falls on to a conveyor belt which carries it away from the seam. Such machines can mine about five tonnes of coal a minute. Sensors can detect how much coal is left in the seam.