Ioun stones (pronounced EYE-oon) are based on similar artifacts from Jack Vance's Dying Earth series. When functioning, they float in a circular pattern around their bearer's head, and grant various benefits based on their color and shape. Two stones of the same type will repel each other, and when drained of power, a stone becomes a dull grey, but still possesses the characteristic floating. While useless to a mage, burned out stones can still yield a single psionic power point to a psionic character in 3rd and 3.5 editions.
In the original Jack Vance stories IOUN stones are highly prized by arch-magicians, and are acquired from a race known as the archveults, who mine them from remnants of dead stars.