Coal is a fossil fuel that is commonly used in producing energy.  It is available in different forms, with some more common and more useful than others.

The use of coal in energy production causes many major problems, usually on a greater scale than the use of oil or gas.  Coal-burning produces acid rain, sulfur oxide emission, carbon dioxide emission, poorer land, hazardous waste, and other problems.

Several forms of coal exist in the world.  Anthracite, bituminous coal, lignite, and sub-bituminous coal are all different types that are used by humans.

Anthracite, also called hard coal, is 86% carbon, a higher percentage than in other forms.  Previously, anthracite was one of the favored forms of coal and US consumption in 1917 reached 100 million tons.  Now, however, anthracite use is declining in favor of oil and natural gas.

Bituminous, or soft, coal, is available in greater quantities but is of a lower quality.  It is available in abundance in the US Appalachian mountains and on the Central Plains. 

Sub-bituminous coal is also widely available and of a higher quality.  It began to be used increasingly after the OPEC oil embargo of 1973.

Lignite, or brown coal, is low quality but it the most widely available form of coal.  Usage is high in Russia and Eastern Europe, and lignite shows promise as a resource of the future.

National Research Center for Coal and Energy