Gelignite was an explosive material which contained in it nitroglycerin. It could be detonated by gunshot or grenade. (TV: Pyramids of Mars, Battlefield) Ernie Clements kept a store of gelignite which he used for fishing. It had started to "sweat", or exude nitroglycerin, making it extremely unstable. The Fourth Doctor used a box of this explosive to destroy the Osiran war missile being created by Sutekh's servitors. Sarah was able to detonate the box by shooting it with a rifle. (TV: Pyramids of Mars)