Coal is an extremely important energy resource. It has several varieties based on the degrees of compression and the depth and time of burial. The following are the different varieties of coal.

• Lignite – This is the lowest quality of coal as it has the least carbon concentration. It is soft brown coal with high moisture content and mainly used in electricity generation.

• Bituminous – This is middle-quality coal with a high heating value. While it appears shiny and smooth, it may reveal a layered appearance on closer inspection. This type is highly popular for commercial use.

• Anthracite – This is the highest quality of coal with a lustrous black appearance. It is hard and brittle with a high percentage of fixed carbon and a low percentage of volatile material. It is mainly used in metal smelting and fabrication industries.

• Peat – contains less than 40-55 per cent of carbon. It also contains a sufficient amount of volatile matter and a lot of moisture.