Coal is formed by a process of compression. Decaying plant matter in swamps is trapped without oxygen, slowing the decay process. This forms peat, a substance with relatively low carbon content which is burned in parts of Europe to heat homes. Peat is considered a "coal precursor," being the substance which eventually develops into coal.
Peat, when compressed, forms lignite, or brown coal. It's often found in Alaska and other Western states in the US. Its carbon content is higher than that of peat, but lower than other forms of coal, and its heat value corresponds to that carbon content as in all the substances discussed here today. It's often used not as a heat source but instead to generate electricity.
The next stage in coal's compression process is bituminous, or black, coal. This is the most common form of coal and almost the only form found in West Virginia. Its carbon content is highly variable, ranging from 45% to 85% concentration, and again, heat value changes accordingly. It is used as a heat source and is also processed into coke for the creation of steel.
A final type of naturally forming coal is anthracite, or hard coal. Unlike at all previous stages of compression, anthracite coal is not a sedimentary rock but a metamorphic one, produced from tremendous heat and pressure put on bituminous coal. It has the highest carbon content of all naturally occurring forms of coal and produces relatively little smoke, making it useful for heating homes.
Coke, as previously mentioned, is a coal product created from bituminous coal. It is heated without oxygen to remove water, tar, gas, and other non-carbon substances. This runoff is used for energy production, while the coke, now at 100% carbon content, is used to make steel.
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