Types of Coal
Coal is defined as "a black or brownish black solid combustible substance formed by the partial decomposition of vegetable matter without free access of air and under the influence of moisture and often increased pressure and temperature." Coal can be burned as fuel or gasified to create a synthesis gas (syngas) that can then be used as a feedstock for the production of chemicals, fertilizer, and/or electric power.

The four types of coal found in the United States are lignite, subbituminous, bituminous, and anthracite. Each type is ranked in quality by the amount of carbon content and heat it can produce.