The colorless, transparent variety of quartz. It is composed of silicon dioxide, the most common mineral in Earth’s crust after ice and feldspar. The name “rock crystal” emerged in the Middle Ages to differentiate it from colorless glass. The Greeks called water-color crystals krystalos, hence the name “crystal.” The name quartz comes from Old German, but its origins are unknown. Metaphysically, quartz is used for power, communication, and cleansing. Found worldwide, fine specimens of quartz can be found in Arkansas, Brazil, and Madagascar.