In the Warhammer
universe, warpstone is the raw stuff of Chaos
, solidified by contact with the material universe. Vast quantities of it were dispersed around the world when the polar warpgates
of The Old Slann
collapsed millenia ago.
It is an extremely unstable form of matter, and also a rich source of magical energy.
Prolonged contact with warpstone causes extreme mutations and death.
The only noticeable exceptions to this rule are the race of ratmen known as Skaven, who have a strange affinity to the stuff.
The elite Skaven sorcerers, the Grey Seers, accumulate magical energy by ingesting warpstone dust.
The warlock-engineers of the Clan Skryre build horrific war machines fuelled on warpstone in various forms
And Clan Moulder use the mutating power of warpstone to genetically engineer beasts of war, such as Rat Ogres.
For this reason, Skaven Clans spend a great deal of effort to collect and stockpile warpstone.
Warpstone is, of course, a thinly-disguised reference to plutonium.