The category is Coal: Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements; chiefly hydrogen, sulphur, oxygen, and nitrogen. Coal is primarily used as a fuel.
Parent categories: Metallurgy, Plastics, Rubber, Chemicals & Energies
Related categories: All categories that are energy related, visitor discretion required