Where does it come from?
And what do you do with it?
Coal is a rock derived from vegetable matter through the process of metamorphism, which requires that heat and pressure act over long periods on this matter, altering both its chemical and physical characteristics. The initial stage of coal formation is peat, decomposed organic matter
The most extensive and most important deposits of coal are in the Appalachian Trough and the interior basins of North America; in Nova Scotia; in Great Britain; in the Belgian, Dutch, and Ruhr deposits in Germany; in Silesia; and in the great Donetz field in Ukraine. All of these latter deposits were formed in the Carboniferous Period, 340 to 280 million years ago.
The United States has approximately 31 percent of the known recoverable coal reserves of the world. At an annual production rate of about 3.5 billion metric tons (3.8 billion U.S. tons) worldwide, serious depletion of resources will take several hundred years. However, coal resources are not inexhaustible; in many areas the best and most accessible coal has already been depleted.
The three main ranks of coal are lignite, bituminous coal, and anthracite. Lignite is closely related to peat but has a lower moisture content. It has the lowest heating value of any of the ranks of coal. Bituminous coal is more dense than lignite and is black in color. Bituminous coal is the most commonly used of the ranks of coal for industrial purposes, both for the generation of electrical power (unless prohibited because of sulfur or other impurities) and for the production of COAL TAR and COKE through destructive distillation. Anthracite is the hardest of all the ranks of coal and typically has a lustrous black appearance. Anthracite has the highest carbon content of any of the coals and burns with the cleanest flame. For this reason, anthracite has been the preferred coal for use as a domestic fuel, although in the United States its main reserves, which are in eastern Pennsylvania, have largely been depleted, limiting both the domestic and industrial use of anthracite.
Although coal was at first gathered from outcroppings, all large-scale early mining was done by underground methods, since none of the large equipment required for surface mining had been developed. The coal was extracted by hand, using picks and bars to remove it from the solid bed. Once extracted, it was shoveled into baskets, boxes, or wheelbarrows and taken outside. Later, mine cars were developed that were drawn over planks covered with iron straps and, eventually, rails. Motor power was supplied by humans, dogs, ponies, mules, and horses. In the late 18th century black powder explosives were introduced to blast the coal. Holes for the explosive were drilled by hand. Undercutting, a procedure in which the coal is cut out from the base of the coal seam to provide a free face for the explosive to break the coal, was also done by hand. Basic machinery developments during the late 1700s and the 1800s, notably the locomotive for transport and the pump for drainage purposes, greatly aided underground coal mining.
Access to underground mines is gained by three primary methods. In the drift mine method, the seam of coal is exposed to the surface on the side of a hill or mountain, and the mine opening is made directly into the coal seam. This is generally the easiest and least expensive way to open an underground coal mine. In the slope mine method, an inclined opening through rock strata is used to gain access to the coal seam. If the coal seam itself is inclined, the slope may follow the seam. In the mine shaft method, the coal seam is reached by a vertical opening from the surface. Combinations of access methods may be used, depending on conditions of the coal seams.
Surface mining, commonly known as strip mining, began in about 1910 when steam shovels began to be used. Today 60 percent of all coal is mined by this method. Strip mining is divided into three general classifications: area, contour, and open pit mining. The area can be mined using either a dragline or a shovel to excavate the overburden in a series of parallel openings. The topsoil is removed first and stockpiled for later reclamation. The overburden from each opening is deposited into the previous opening after the coal has been extracted. Peaks created by this deposition must be leveled and covered with topsoil for reclamation.