Coal is an extremely important energy resource. It has been formed from the compression of plant materials over thousands of years. Coal deposits in India are of two distinct geological ages. The earliest coal deposits are of Permian age formed about 270 million years ago. At that time, South Africa, South America, Antarctica, Australia, India and Madagascar formed a landmass called Gondwanaland. Coal formed in Gondwanaland are known as Gondwana Coal. Other deposits of Tertiary age (30-60 million years) have been formed comparatively recently. These are known as Tertiary Coal. The following table gives the distribution of coal fields in India according to their geological type.

The above is not an exhaustive list but merely an indicator of the important coal sources according to geological type in India. Coalfields are present in almost all the states of India.