Coal is a solid but brittle, carbonaceous black sedimentary rock that burns. It is made up of carbon, hydrogen, oxygen, nitrogen, and lesser amounts of sulfur and other trace elements. Coal is divided into four classes: lignite,sub bituminous, bituminous, and anthracite. Of the commonly minable coals, anthracite is the hardest and has the most carbon, giving it a higher heat value. Lignite is the softest coal and has the least amount of carbon. By definition, coal isa combustible rock containing more than 50 percent by weight carbonaceous material formed from compaction of variously altered plant remains originally derived from peat industry Description and Practices Coal is one of the world’s most plentiful energy resources, and its use is likely to quadruple by 2020. Coal occurs in a wide range of forms and qualities; but there are two broad categories:

a) hard coal, which includes coking coal, used to produce steel, and other bituminous and anthracite coals used for steam and power generation,and
b) brown coal (sub bituminous and lignite),which is used mostly as onsite fuel.

Coal has a wide range of moisture content (2–40%), sulfur content (0.2–8%), and ash content (5–40%). These can affect the value of the coal as a fuel and cause environmental problems in its use. The depth, thickness, and configuration of the coal seams determine the mode of extraction. Shallow, flat coal deposits are mined by surface processes, which are generally less costly per ton of coal mined than underground mines of similar capacity. Strip mining is one of the most economical surface processes. Here removal of overburden and coal extraction proceed in parallel strips along the face of the coal deposit, with the spoil being deposited behind the operation in the previously mined areas.

In open pit mining, thick seams (tens of meters) are mined by traditional quarrying techniques. Underground mining is used for deep seams. Underground mining methods vary according to the site conditions, but all involve the removal of seams followed by more or less controlled subsidence other overlying strata. Raw coal may be sold as mined or may be processed in a be neficiation washing plant to remove noncombustible materials (up to 45%) reduction in ash content and inorganic sulfur (unto 25% reduction).