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

Sub bituminous coal has a higher heating value than lignite. Sub bituminous coal typically contains 35-45 percent carbon, compared to 25-35 percent for lignite. Most sub bituminous coal in the U. S. i

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