Coal is a combustible black or brownish-black sedimentary rock with a high amount of carbon and hydrocarbons. Coal is world's leading mineral fuel,it burned to produce heat which is used to generate electric power. Coal is classified as a nonrenewable energy source because it takes millions of years to form. Coal contains the energy stored by plants that lived hundreds of millions of years ago in swampy forests.
It may be defined as a solid stratified rock composed mainly of corboniesd plants.
Rank of coal - The process of conversation of vegetable matter to coal involves loss of oxygen and hydrogen contents and increase the concentration of carbon.
The progressive elimination of water, oxygen, and hydrogen and increase in carbon from low rank to high rank.
Coal rank is the measure of the degree of organic metamorphism (coalification) of a coal, ranging from
low-rank peat, Lignite, sub-bituminous, Bituminous, to high-rank Anthracite.
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