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 Coal is formed from plant life buried in the Earth millions of years ago. Like Petroleum and natural gas, it is a carbon-based fossil fuel.  Coal is called a fossil fuel b â¦ ecause it was formed from the remains of vegetation that grew as long ago as 400 million years.
The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Lignite, or brown coal, is the lowest rank of coal and used almost exclusively as fuel for electric power generation. 2  Jet, a compact form of lignite, is sometimes polished and has been used as an ornamental stone since the Upper Palaeolithic.