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Where is Coal Found?

Coal measures occur in many countries around the world. China is believed to have the greatest reserves, around 40% of the total, and Russia has large quantities of both coal and lignite, though much of it is in inaccessible regions of Siberia. North America also has significant deposits.
In continental Europe the most important reserves are around the Ruhr valley in Germany, in Poland and in the Ukraine.
In the United Kingdom the main coal fields are in South Wales, Yorkshire, Derbyshire, Nottinghamshire, Northumberland and central Scotland, as shown in this map:

Black areas are the main coal deposits in Britain.

In the early 1980s British coal production was around 100 million tonnes per year, with recoverable reserves of coal estimated at 45 billion tonnes, out of a total reserve (mostly inaccessible) of maybe 160 billion tonnes.

The Nottinghamshire and Derbyshire coal field in fact extends eastwards under the North Sea and some natural gas, from the southern part of the North Sea, originates from these underlying coal measures.

The types of animals which lived in the forests which became coal swamps included crabs and shrimps, and particular types of mussels in lakes within the forests. If test boreholes yield mussel fossils of the correct species this can be be used to predict the presence of coal deposits in the area. This technique was used in Britain in the mid 20^th century to find the new coal supplies needed for expanding industry.

Types of Coal

(Most of this section is derived from the 'International Correspondence Schools' manual on 'Fuels, Steam and Steam Engines', 1907.)
Coal varies in its composition and physical properties according to the precise conditions under which it formed. The main division is into bituminous coal and anthracite coal.
Bituminous coal is the most common variety. It is clearly seen to consist of alternating dull and shiny layers and is soft, soiling anything it touches.
Anthracite has a higher carbon content than bituminous coal and contains less volatile material. It is hard and shiny and can be handled without soiling. Anthracite is formed when bituminous coal is subjected to especially high pressures by the rock strata being folded, e.g. during mountain range building. Anthracite is relatively rare; the only significant UK source is the South Wales coalfield.

When coal was the most important fuel it was further classified according to the use for which it was suitable.

• Domestic coal burns with a clear flame and leaves behind a small proportion of brownish ash which does not block the fire grate. It should remain lit at low temperature with minimal draught. Coal which burns with a minimum of smoke and which has a low sulphur content is preferred, to avoid too much soot or strong odours.
• Gas coal was distilled to yield coal gas (mostly a mixture of hydrogen, methane and carbon monoxide) for lighting. A gas coal therefore needs to contain a large amount of volatile hydrocarbons, typically 30 to 40 percent.
• Cannel coal was so called because it could be lit and burnt with a luminous flame like a candle. It is quite high in volatile components and was used as a source of oil and coal gas. Cannel coal is hard and can be readily polished, and is sometimes carved into ornaments.
• Blacksmith's coal, used in forging iron, must have a low sulphur content otherwise the sulphur is absorbed into the iron and weakens it.
• Steam coal was used to heat the boilers of steam engines. Coal which burns quickly but without significant smoke is necessary, because smoke would deposit as soot on the boiler tubes and reduce the efficiency of heat transfer. This means a medium amount of volatile matter is best and a type known as 'semi-bituminous', intermediate between bituminous and anthracite, was preferred. All coal leaves a residue of ash which is non-combustible inorganic matter, the remains of soil and dirt which collected in the swamps along with the plant remains. If the ash has a low melting point it can fuse together when the coal is burnt, leaving a solid mass called clinker which will block the grate. Good steam coal should not form clinker.

Notice how in changing from peat to anthracite the oxygen content reduces greatly because of loss of water, and the calorific value (how much energy is obtained by burning it) goes up.

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