Coal is a solid, opaque, inflammable substance, mainly consisting of carbon, found in the earth, largely employed as fuel, and formed from vast masses of vegetable matter deposited through the luxuriant growth of plants in former epochs of the earth's history. In the varieties of coal in common use the combined effects of pressure, heat, and chemical action upon the substance have left few traces of its vegetable origin; but in the sandstones, clays, and shales accompanying the coal, the plants to which it principally owes its origin are presented in a fossil state in great profusion, and frequently with their structure so distinctly retained, although replaced by mineral substances, as to enable the microscopist to determine their botanical affinities with existing species.
The sigillaria and stigmaria, the lepidodendron, the calamite, and tree-ferns are amongst the commoner forms of vegetable life in the rocks of the coal formation. Trees of considerable magnitude have also been brought to light, having a recognizable relation to the modern araucaria. The animal remains found in the coal-measures indicate that some of the rocks have been deposited in fresh water, probably in lakes, whilst others are obviously of estuarine origin, or have been deposited at the mouths of rivers alternately occupied by fresh and salt-water. The great system of strata in which coal is chiefly found is known as the Carboniferous. There are many varieties of coal, varying considerably in their composition, as anthracite, nearly pure carbon, and burning with little flame, much used for furnaces and malt kilns; bituminous (popularly so called) or 'household coal'; and cannel or 'gas-coal,' which burns readily like a candle, and was much used in gas-making. The terms semi-anthracitic, semi-bituminous, caking-coal, splint coal, etc, are also applied according to peculiarities. All varieties agree in containing from. 60 to over 90 per cent of carbon, the other elements being chiefly oxygen and hydrogen, and frequently a small portion of nitrogen.
Lignite or brown coal may contain only 50 per cent of carbon or less. For manufacturing purposes coals are generally considered to consist of two parts, the volatile or bituminous portion, which yields the gas used for lighting, and the substance comparatively fixed, usually known as coke, which is obtained by heating the coal in ovens or other close arrangements, and thus removing the volatile or smoke-yielding matter, while the full heating power of the coal still remains in the coke. Coal was the most valuable of all the minerals which contributed to the former wealth of Great Britain, and it has been mined there for many centuries. The first charter giving liberty to the town of Newcastle-upon-Tyne to dig coal was granted by Henry III in 1239; in Scotland a charter was granted to the abbot and convent of Dunfermline in 1291 for the same purpose. The working of coal gradually but slowly increased, until towards the end of the 18th century, when the development of the steam-engine by James Watt enormously increased the use of coal, and made it the basis of Great Britain's industrial importance. Towards the end of the 20th century political disputes between the miners and the government led to the closure of most of Britain's coal mines, with coal being imported instead. Research Coal
Abbreviations
Rocks & Minerals
Research Coal