Quartz

a mineral compound of silicon and oxygen. It is one of the most abundant rock materials, constituting large masses, as well as the sands of the desert and the seashore. Crushed it forms a beautiful sand. It enters into the make-up of granite, gneiss, quartzite, and sandstone. It is hard, scratching glass easily, and cannot be melted at ordinary temperatures or dissolved by ordinary acids. For this reason, glass, which is chiefly quartz, is valuable in a laboratory and in the household. Many varieties of pure quartz are colored, as rose quartz, the opal, the amethyst, the smoky quartz, chalcedony, sardonyx, agate, carnelian, onyx, and agatized wood. Pulverized quartz is frequently used in preference to sand, being clearer and purer, for making glass and porcelain. It is also used for making sandpaper, as the crushed particles have a fresher, sharper fracture than worn sand. The mineral known as pebble, used for spectacles, is a transparent quartz. See Sand; Silicon