Coal the heat and pressure of deep burial causes the loss of water, methane and carbon dioxide and an increase in the proportion of carbon. Thus first lignite (also called "brown coal"), then sub-bituminous coal, bituminous coal, and lastly anthracite (also called "hard coal" or "black coal") may be formed. The wide, shallow seas of the Carboniferous Period provided ideal conditions for coal formation, although coal is known from most geological periods. The exception is the coal gap in the Permian–Triassic extinction event, where coal is rare. Coal is known from Precambrian strata, which predate land plants—this coal is presumed to
Coal mining in the United Kingdom at ordinary combustion temperatures (i.e. for the oxidation of carbon - see fossil fuels). The last deep coal mine in the UK closed on 18 December 2015. Twenty-six open cast mines still remain open and Banks Mining said in 2018 they planned to start mining a new site in County Durham. The United Kingdom's onshore coal resources occur in rocks of the Carboniferous age, some of which extend under the North Sea. The carbon content of the bituminous coal present in most of the coalfields is 86% to 88%. Britain's coalfields are associated with Northumberland and Durham, North and South