1. Peat: Peat is the first stage of coal development. It is dark brown in colour. It has about 35 per cent carbon content.
2. Lignite: Lignite is the next stage of coal formation, which has almost 50 per cent carbon.
3. Anthracite: Lignite becomes sub-bituminous, bituminous and eventually anthracite coal. Anthracite has more than 85 per cent carbon. It is the best quality of coal. It is very hard, compact, black in colour. It ignites slowly and bums with short blue flame.
