In legend, a sorcerer who specialized in working with magic based on & in gems & crystals, up to & including Sancrist Crystals.
The last Crysmage was said to have been killed in the Myth Wars before the coming of Men to Alair. One of the last recorded crysmagi was Forlendel, who aided Galoriand and Elverandil in the capture and imprisoning of Cain.