FORM OF CARBON is a term used to describe three different substances: CHARCOAL, DIAMOND, and SOOT. CHARCOAL is an 8-letter substance made from burning wood or other organic materials in the absence of oxygen. DIAMOND is a 7-letter substance that is the hardest naturally occurring material on Earth and is composed of pure carbon atoms arranged in a crystal lattice structure. SOOT is a 4-letter substance that is a black powdery or flaky substance composed of carbon particles that are produced by the incomplete combustion of fossil fuels.