Anthracite is the highest ranked, hardest, oldest, and least common type of coal. It possesses a high energy content, high percentage of carbon (>85%) and relatively little moisture or volatiles. Anthracite produces nearly 15,000 Btu's per pound.
Bituminous is the second rank of coal, softer and younger than anthracite, and containing a lower percentage of carbon (45-85%) and therefore more moisture and volatiles. Bituminous coal is primarily used to generate electricity and to make coke for the steel industry. It has a heat value of 10,500 to 15,500 Btu's per pound. Subbituminous coal ranks just below bituminous coal with 35 to 45 percent carbon content. The heat value of subbituminous coal is between 8,300 and 13,000 Btu's per pound.
Lignite has the softest, youngest, and wettest rank of coal with a carbon content of only 25-35%. The heat value of lignite ranges between 4,000 and 8,300 Btu's per pound. Sometimes lignite is known as brown coal because of its brown color.
Peat – contains less than 40-55 per cent of carbon. It also contains a sufficient amount of volatile matter and a lot of moisture.