1) Pest – It is an impure form of coal. It has the lowest percentage purity.
2) Lignite – It is a type of coat, which is purer than peat. It is known as brown coal and is formed when peat Is pressurized.
3) Bituminous – This is a type of cost which comes after lignite coal and is of very high purity. It is also called soft coal.
4) Anthracite – This is the purest form of coal. It is also known as hard coal.