ABSTRACT
Coal Coal is the compressed remains of tropical and subtropical plants, predominantly from the Carboniferous and Permian periods 225 million to 345 million years ago. Coal includes varying levels of carbon, hydrogen, sulfur, and nitrogen. Coals are classified according to their carbon content, from the lowest to the highest, as lignite, subbituminous, bituminous, and anthracite. Coals with higher concentrations of carbon are harder and hold more energy. Lignite, with the least energy available to burn, is the most abundant in the United States; high-energy anthracite is relatively rare. In general, coals from the eastern and
midwestern United States are bituminous, with high heat values but high levels of acid-rain-causing sulfur as well. Coals from the western states are largely subbituminous or lignite, with low heat value and low sulfur content. Pennsylvania holds most of the country’s anthracite supply.
