Coal is formed due the compression of plant material (containing carbon, the major component of coal) over millions of years.
Thus, coal is found in many forms depending on the degrees of compression, the depth and the time of burial. Indian coal was mainly formed during two geological ages the Gondwana and the Tertiary ages.
The Gondwana coal deposits (called ‘metallurgical coal’), which are more than 200 million years old, are located in the Damodar valley (West Bengal - Jharkhand), where Jharia, Raniganj and Bokaro are important coal Reids.
It is also found in the Godavari, Mahanadi, Son and Wardha valleys.
The tertiary age deposits, only about 55 million years old, are mostly found in North-Eastern : India in Meghalaya, Assam, Arunachal Pradesh and Nagaland.
Thus, formation of coal is a long drawn process spread over various periods, Thus, consumption of energy in all forms has been rising all over the country.