Coal is classified into four main types or ranks (lignite, sub bituminous, bituminous, anthracite) , depending on the amounts and types of carbon it contains and on the amount of heat energy it can pr

Bituminous coal contains 45-86 percent carbon, and has two to three times the heating value of lignite. Bituminous coal was formed under high heat and pressure. Bituminous coal in the United States is

Anthracite contains 86-97 percent carbon, and has a heating value slightly lower than bituminous coal. It is very rare in the United States, accounting for less than one-half of a percent of the coal