The colorless, transparent variety of quartz 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.” “Quartz” comes from Old German, but its origins are unknown. Metaphysically, quartz is used for power, communication, and cleansing. Found worldwide, most fine quartz comes from Arkansas, Brazil, and Madagascar.