Coal

The industrial revolution in 18th-century Europe and North America was propelled by a black rock called coal. Modern industrial civilization still continues to depend heavily on this rock. The word coal is of Anglo-Saxon origin from the word col, which means charcoal. Historians note that coal was already under use during the Bronze Age (around 2000 b.c.e.) in Britain. By 200 c.e., coal was being widely traded in Britain and used for fires to heat villas and military forts and also to dry grain. However, before 1000 c.e., the trade and use of coal was on a small scale. It was not until 1000 c.e. that coal began to be a prominent commodity in Britain. Initially, exposed coal seams [Page 288]were exploited, but by the 13th century these were exhausted, necessitating the development of underground mining from shafts.

Coal is a fossil fuel formed from prehistoric vegetation that originally accumulated in swamps and peat bogs and then consolidated between other rock strata. Silt and other sediments buried these swamps and peat bogs at great depths. This subjected the plant matter to high temperatures and pressure, which in turn transformed the vegetation into peat and then into coal. It is believed that coal formation began during the Carboniferous period about 360–290 million years ago. In Europe, Asia, and North America, the Carboniferous coal was formed from tropical swamp forests, which are sometimes called the coal forests. Southern hemisphere Carboniferous coal was formed from the Glossopteris flora, which grew on cold periglacial tundra when the South Pole was far inland in Gondwanaland.

Through the process of coal formation (coalification) over millions of years, various states of coal have been formed, resulting in different types of coal and coal seams that can be extracted via deep or underground mines or open pit mining. There are four main types of coal that range from high water content to high carbon content: peat (lignite or brown coal), sub-bituminous, bituminous, and anthracite. Peat and sub-bituminous coal are ranked as low coal, as they have high water content and low carbon content, while bituminous and anthracite are ranked as hard coal with a very high carbon content and therefore high energy output. The term dirty black rock comes from the highly ranked hard coal with a black luster, while the low-ranked coal is softer with a brown or earthy appearance.

Carbon accounts for more than 50 percent by weight and more than 70 percent by volume of coal, depending on the rank. Highly ranked coals contain 95 percent purity of carbon with less hydrogen, oxygen and nitrogen. Coal also contains incidental moisture, which is why coal is mined wet and stored wet. Low-ranked coals, such as lignite, contain considerable amount of moisture and other volatile materials known as macerals. These macerals are byproducts of the long process of coal formation from carbohydrate material into carbon over millions of years. Examples of macerals are vitrinite (fossil woody tissue, often charcoal from forest fires); fusinite (made from peat); exinite (fossil spore casings and plant cuticles); resinite (fossil resin and wax); and alginite (fossil algal material). Coal may also contain other mineral matter such as silicate, carbonate minerals, iron sulfide minerals, and sulfate minerals. Methane gas is also a major valuable byproduct for natural gas, but also an extremely dangerous component, as it often causes coal seam explosions in underground mines. The presence of these extraneous materials in coal seams determine the chemical composition of coal and therefore its utility for various tasks.

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