A common non-metallic element that occurs in many inorganic and in all organic compounds, exists freely as graphite and diamond, and as a constituent of coal, limestone, and petroleum, and is capable of chemical self-bonding to form an enormous number of chemically biologically, and commercially important molecules. It is an important ingredient in steel and other alloys. Its elemental symbol is C; atomic weight 12.01115. The specific gravity of amorphous carbon is 1.8 to 2.1, of diamond 3.15 to 3.53, and of graphite 1.9 to 2.3. Also, may refer to a sheet of carbon paper, or an image produced by marks made to carbon paper.