The Nabaal Crystal is a crystal shard from the world of Nabaal, visited by the Draenei on their long exodus across the cosmos. Nabaal fell eons ago to the might of the Burning Crusade, but vestiges of its legacy carry on in the form of the Nabaal Crystals.
Possessing a natural ability to detect the presence of Fel magics, Nabaal Crystals vibrate and change to a crimson shade to varying degrees depending on the potency of local Fel taint.