CRYSTAL, or Rock Crystal, is a popular name for Quartz, or pure crystalline silex, the finest and largest crystals of which are found in Madagascar Dauphine, and the Alps; the so called Bristol diamonds are nothing but fine specimens of quartz cut and polished.

The Brazilian pebbles for spectacles are lenses ground out of pure, transparent, colourless quartz, the stone is cut into slices by the lapidary, afterwards it is snipped into the form of the lenses, with nippers which resemble wide flat pliers, and are made of soft iron, in order that the quartz or glass may slightly imbed itself, to gain a hold, which could not take place with the hard steel faces of ordinary pliers; lastly the pieces of crystal are ground into the form of lenses and polished by the optician, exactly in the same mode that he employs for glass lenses, and which will be described.

Many remarkable specimens of cups, tazzas, and other works of art have been formed by abrasion from the beautiful material rock crystal, or quartz; some of these may be seen in the British Museum, and excite astonishment by the laborious perseverance they evince.