coal - fossil fuel consisting of carbonized vegetable matter deposited in the Carboniferous period

humate - material that is high in humic acids

jet - a hard black form of lignite that takes a brilliant polish and is used in jewellery or ornamentation

atomic number 6, carbon, C - an abundant nonmetallic tetravalent element occurring in three allotropic forms: amorphous carbon and graphite and diamond; occurs in all organic compounds

fuel - a substance that can be consumed to produce energy; "more fuel is needed during the winter months"; "they developed alternative fuels for aircraft"