Warpstone is an emerald green crystal that resembles jade from its appearance, formed from condensed Dhar (Dark Magic). Warpstone is very dangerous, because it has very strong mutating powers capable of transforming nearly any organic lifeform, and because of these mutagenic properties is considered by many to be the very essence of Chaos.
Warpstone has been known to be somewhat addictive if consumed in small amounts. The Skaven wizards (Grey Seers) are often found with a high addiction to Warpstone, because of the way they use it to enhance their magical power greatly (however dangerous it may be to their health in the process of doing so). Warpstone is so popular in Skaven trade that it can be even considered their currency, as well as their primary resource (it is used in various war-machines of the Skaven). Over thousands of years the Skaven have become masters of the use of warpstone in spells. Skaven war over warpstone deposits to use in their industry. Warpstone is most often found in the Chaos Wastes, but can also be found in areas with a high concentration of Dark Magic, or raw, unrefined magic in general. In The Empire, Kislev and in the rest of the Old World's human nations, there is a prevalent black market trade in bags of warpstone powder/dust, small pieces of warpstone, and trinkets that have been infused with essence of warpstone. Here it is commonly known as 'Wyrdstone' and the superstitious believe it can turn other metals into gold and cure sickness. Some wizards foolishly believe that wyrdstone and warpstone are two different substances. They think wyrdstone can be used to heal sicknesses and increase their magical ablities. These unfortunate, foolish men soon find themselves corrupted by chaos and madness.
Dwarfs tend to stay clear of warpstone, though rogue Engineers may experiment with it. Dark Elves often magically experiment with the substance. While Elves seem to be immune from the mutating effects of Warpstone for the most part, high concentrations may have a detrimental effect on their sanity over time.