Crystal, a species of stone, of various colours, of which that most generally known is the peb-ble-crystal, or sprig or rock-crys-ial, as it is usually called. It is common in this country, and is frequently cut into chandeliers, vases, lustres, and other ornamental articles. Even this hard and beautiful mineral has often been used in medicine, as an astringent and lithontriptic : it was formerly given iu diarrhoeas, and in cases of stone in the kidnies. The dose usually prescribed is from 20 to 30 grains, finely pulverized by repeatedly calcining and plunging it in cold water. It has likewise been recommended as a dentrifice, but like other hard bodies, it is apt to corrode the teeth, and consequently renders them more liable to decay.