A piece of bone from one of the many draconic species of the Continent. The older the drake, the more powerful the magic stored in their bones.
True dragons are sentient, and tend to leave mortals well alone. Drakes and wyverns, however, have nearly as much potency in their bones, and a tendency to snack on mortals and their livestock. The killing of a true dragon is punishable by death if not done by a warranted officer of whatever nation you’re in, but hunting down a drake or wyvern is often a lucrative endeavor if you can survive its breath or venomous tail.