a. Gondwana Coal: Coal formed about 350 million years ago in the Carboniferous age is called Gondwana Coal. The Gondwana coal is a laminated bituminous coal within which dull and bright layers alternate. Gondwana coal is almost free from moisture, but it contains variable quantities of sulphur and phosphorus. In general, Gondwana coal is good steam or gas coal.
b. Tertiary Coal : Coal formed about 50 million years ago in the Tertiary period is called Tertiary coal. This coal consists mostly of lignite and peat.
