Gelignite was an explosive material invented by Alfred Nobel in 1875. More stable than his earlier creation dynamite, gelignite was easily mouldable and safer to handle.
Ernie Clements kept a store of gelignite which he used for fishing. It had started to "sweat", or exude nitroglycerine, making it extremely unstable. The Fourth Doctor used a box of this explosive to destroy the Osirian war rocket being created by Sutekh's servitors. Sarah was able to detonate the box by shooting it with a rifle. (DW: Pyramids of Mars)
In the real world, gelignite is much more stable than dynamite. It doesn't sweat and can't be exploded without a detonator, so it is possible that Clements really used dynamite.
