Chemical explosives can be classified as low or high explosives. Low (or deflagrating) explosives are used primarily for propelling; they are mixtures of readily combustible substances (e.g., gunpowder) that when set off (by ignition) undergo rapid combustion. High (or detonating) explosives (e.g., TNT) are used mainly for shattering; they are unstable molecules that can undergo explosive decomposition without any external source of oxygen and in which the chemical reaction produces rapid shock waves. Important explosives include trinitrotoluene (TNT), dynamite, nitrocellulose, nitroglycerin, and picric acid. Cyclonite (RDX) was an important explosive in World War II. Ammonium nitrate is of major importance in blasting.