Vickipedia

CRYSTALLO’MANCY, a mode of divination by means of transparent bodies, at one time very popular. A precious stone, crystal globe, or other transparent object, was employed, but a beryl was deemed most effective. In using it, the operator first muttered over it certain formulas of prayer, and then gave it into the hands of a youth or virgin�none others were pure enough to discern its revelations�who beheld in it the information required. Sometimes the desiderated facts were conveyed by means of written characters on the crystal; sometimes the spirits invoked appeared in the crystal to answer the questions asked.