There are different grades. Coal has three main types, or grades. They are lignite, bituminous, and anthracite. Lignite is the swampy peat that squeezed and heated to form a brown, soft coal. With more heat and pressure added to the lignite, hydrocarbons are released and it then becomes the next higher-grade. Bituminous coal is black and hard. With even more heat and pressure the highest grade is yielded to become anthracite.
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