Common type of coal is –

Explanation

Coal is mainly a mixture of free carbon and carbon compounds. Through the chemical process of carbonization, plant material gets converted into coal. Coal is mainly of four types— Anthracite, Bituminous, Sub-bituminous, and Lignite. Among these four types, bituminous coal is considered the common variety. Anthracite is the best quality coal. In India, about 99 percent of the total coal found occurs in ancient Gondwana rocks. Gondwana-age coal is mainly of the bituminous type.