Coal

Coal is the most abundant fossil fuel, though its global distribution is highly uneven, and it powered the Industrial Revolution. Readily combustible and solid, it is formed in ecosystems where plant matter has been preserved by water and mud from oxidation and biodegradation. The fuel is black, brownish-black, or brown. Coal reserves are classified into categories or ranks based on the degree of coalification, or progressive alteration, that has occurred over time—this refers to changes in its energy and carbon content and environmental constituents. Ranks include anthracite (most desirable), bituminous (most abundant), subbituminous, and lignite (least desirable). Coal use often has been limited because of high emissions of sulfur dioxides, nitrogen oxides, particulates, and, most recently, carbon dioxide (it has the highest carbon emission rate ...