For the magic-user that wants a boost in power, or wants to make a magically-charged item, mana crystals are the answer. These crystals are about as rare as diamond, and are just as valuable - not for their looks, but for the power they contain. They act as a sort of magical battery, able to extend a mage's power for a time until they lose their energy. There's rumors that the largest mana crystals never run out of power, but no one can agree exactly what size the 'largest' ones are.
Mana crystals can often be found deep in the earth, and have been known to appear around shrines and other sites of power. The floating island of Nahk is the largest source of mana crystals found anywhere, though veins of mana crystals have been known to appear deep in the Badlands Mountains.
The advantages might seem too good to be true, and to a certain extent, they are. Areas with mana crystals have been known to cause very strange magical effects in the surrounding areas. There's been stories animals and inanimate objects being blessed with intelligence, of day being turned to night and vice-versa, and some people even claim that mana crystals can make the dead walk again.