Coal is the product of vegetable matter that has beenvformed by the action of decay, weathering, the effects of pressure, temperature and time millions of years ago.
Although coal is not a true mineral, its formation processes are similar to those of sedimentary rocks.
According to the amount of carbon coals are classified into; brown coals, bituminous coals and anthracite. Brown coals are in their turn subdivided into lignite and common brown coal.
Although carbon is the most important element in coal, as many as 72 elements have been found in some coal deposits, including lithium, chromium, cobalt, copper, nickel, tungsten and others.
Lignite is intermediate in properties between peat and bitumi- nous coal, containing when dry about 60 to 75 per cent of carbon and a variable proportion of ash. Lignite is a low-rank brown-to-black coal containing 30 to 40 per cent of moisture. Developing heat it gives from 2,500 to 4,500 calories. It is easily inflammable but burns with a smoky flame. Lignite is liable to spontaneous combustion. It has been estimated that about 50 per cent of the world's total coal reserves are lignitic.
Brown coal is harder than lignite, containing from 60 to 65 per cent of carbon and developing greater heat than lignite (4,000-7,000 calories). It is very combustible and gives a brown powder. Bituminous coal is the most abundant variety, varying from medium to high rank. It is a soft, black, usually- banded coal. It gives a black powder and contains 75 to 90 per cent of carbon. It weathers only slightly and may be kept in open piles with little danger of spontaneous combustion if properly stored. Medium-to-low volatile bituminous coals may be of coking quality. Coal is used intensively in blast furnaces for smelting iron ore. There are noncoking varieties of coal.
As for the thickness, the beds of this kind of coal are not very thick (1-1.5 metres). The great quantities of bituminous coal are found in the Russian Federation.
Anthracite or "hard" coal has a brilliant lustre containing more than 90 per cent of carbon and low percentage of volatile matter. It is used primarily as a domestic fuel, although it can sometimes be blended with bituminous grades of coal to produce a mixture with improved coking qualities. The largest beds of anthracite are found in Russia, the USA and Great Britain.
Write an abstract of the text “ Coal and Its Classification” according to the plan:
1. The classification of coal.
2. The characteristic of lignite, brown coal, anthracite