Depending upon the amount of carbon content, coal may be of four types:

Peat: This is the most inferior and softest form of coal. Its carbon content is very low. It has a large amount of moisture and is not much suitable to be used as fuel.

Lignite: Lignite is comparatively harder than peat, but still is very soft. Its carbon content is more than that of peat.

Bituminous: Its carbon content is higher, as it is free from moisture and other impurities.

Anthracite: This is the highest-grade coal. This is also known as hard coal. It has maximum amount of carbon. It produces a very little smoke.