Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. Coal is the largest source of energy for the generation of electricity worldwide, as well as one of the largest worldwide anthropogenic sources of carbon dioxide releases. Coal is extracted from the ground by coal mining, either underground by shaft mining, or at ground level by open pit mining extraction.
Examples of Application
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. Approximately 4% of the coal mined in the United States is exported, and most of the exported coal is used for making steel