ABSTRACT
Carbon is the fifteenth most abundant element in the earth’s crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. Carbon is also present as a major component in large masses of carbonate rocks, including limestone, dolomite, and marble. Coal is the largest commercial source of mineral carbon, accounting for nearly 8 billion tons or almost 80% of fossil carbon fuel. In its elemental form, carbon (C, atomic number 6) has a valency of 4 and is therefore placed in group IV of the periodic table along with Si, Ge, Sn, and Pb.
