Coal is a combustible rock made of carbon, hydrogen and oxygen. Heat and pressure have made vegetation - which absorbed energy from sunlight - into coal over the course of millions of years, starting in the Carboniferous period. It's the most available and abundant fuel source we've got; and there's at least 112 years worth of coal left. We use coal to generate electricity by burning it - the magic of Christmas cheer can't power a car, after all. Coal takes on different properties, and is therefore ranked, by how far it has undergone coalification. It may be anywhere between Peat and Anthracite, depending on how much of the original plant material has been converted to carbon.
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