Coal

Coal is a carbonaceous rock which occurs as a result of anaerobic decomposition of plant matter and lithification of the resulting material. Coal occurs in three main forms: anthracite, bituminous coal, and lignite, depending on the degree of lithification.

Chemical composition

Coal is primarily carbon, with traces of sulfur, oxygen, hydrogen, nitrogen, and other elements. The processes of decomposition and lithification drive off most of the oxygen, hydrogen and nitrogen from the plant material, leaving primarily carbon.

Economic use

Due to its high carbon content and solid, easily-handled form, coal is used for fuel, and has been for hundreds of years (see history of coal mining). Coal can be burned directly, or it can be converted to coke by anaerobic heating (called coking), which alters the physical properties to provide a more uniform and more combustible product. Coal is used in steelmaking both to provide heat and to add controlled amounts of carbon to the iron.

Large-scale exploitation of coal began concurrently with the Industrial Revolution, and coal was one of its primary ingredients. Coal was used to make iron, and later steel, and was used to power steam engines which were used to transport very large quantities of goods (relative to previous animal-driven transport) and to pump out deep mines of coal and iron.

Currently, burning of coal provides about one-quarter of the electric power of the United States, and accounts for about one-quarter of energy use worldwide. About 90% of coal mined in the United States is burned to produce electricity.

Coal mining

Coal deposits are found in many places around the world, though the deposits which have had the largest economic impacts are those in the Rhine/Ruhr area of Germany, Wales and the Midlands of England, and the upper Ohio Valley of the United States. Currently, coal production in China is rapidly increasing to meet soaring demand from China's industrialization.

Coal mining takes two forms: open-pit, or strip, mines, and deep mines. Open-pit mines are used when coal deposits are shallow; overburden deposits are removed from the site, and coal is excavated from the ground in what becomes large pits. These mines can become quite deep, and when open-pit mines are played out, the mining company often abandons the site with no restoration. Deep mines are similar to those for any other mineral deposit found deep enough in the earth that the cost of removing the overburden is prohibitive. Shafts are dug and veins of coal are excavated and transported to the surface.

Coal mining is very dirty and very hazardous work; the poor conditions of coal mines led to early labor unions being formed among mine workers; mineworkers' unions earned a reputation for activism.