Answer: Bituminous coal is the most popular coal in commercial use.
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Coal in India:
Coal is found in a variety of forms depending on the degrees of compression and the depth and time of burial.
Decaying plants in swamps produce peat. It has a low carbon and high moisture contents and low heating capacity.
Lignite is a low-grade brown coal, which is soft with high moisture content.
The principal lignite reserves are in Neyveli in Tamil Nadu and are used for generation of electricity.
Bituminous coal is the most popular coal in commercial use.
Metallurgical coal is high grade bituminous coal which has a special value for smelting iron in blast furnaces.
In India coal occurs in rock series of two main geological ages;
Gondwana: A little over 200 million years in age and
Tertiary deposits which are only about 55 million years old.
The major resources of Gondwana coal, which are metallurgical coal, are located in Damodar valley (West Bengal-Jharkhand). Jharia, Raniganj, Bokaro are important coalfields.
The Godavari, Mahanadi, Son and Wardha valleys also contain coal deposits.
Tertiary coals occur in the north eastern states of Meghalaya, Assam, Arunachal Pradesh and Nagaland.