Author Larry Correia has a fantasy book series called the "Saga of the Forgotten Warrior." in the books, a group of evil wizard assasins plague the hero.
Interestingly enough, they get their powers not from communing with nature, praying to gods or studying scrolls. No, these wizards use bits of a material called "black steel" or from the body parts of creatures they call demons to power their spells which crumble into dust upon completion of the spell.
Replace black steel and demon bits with gems and stones and you have a fascinating representation of the Geomancer.