Rock crystal on a stand from the famous Coleman mines, Arkansas, USA.

Rock crystal is the colorless and most common variant of the mineral quartz (silicon dioxide, SiO2). The name 'rock crystal' is derived from the Greek word 'Krustallos,' which means ice. People believed that rock crystal was ice shaped by the gods. At the time of the Mesolithic, people were already familiar with rock crystal. During the Roman period, it was marketed from the Alps under the name 'frozen ice.' Theophrastus called it "kristallos." Pliny the Elder also mentions it. The name 'quartz' was introduced in 1529 by Georgius Agricola. The peoples from the East regarded rock crystal as the stone of patience and perfection. Tibetans use rock crystal to treat wounds.The choice of rock crystal as a drinking glass or as part of medieval jewelry can be attributed to the belief that these crystals would break or change color when they came into contact with poison. Thus, the chain became an amulet that protected the king. Compare the Rudolfine Imperial Crown and the chain of the Order of Jehovah. Origin: magnetites, pegmatites, hydrothermal and alpine veins, alluvial deposits. Occurrence: rock crystal is widely distributed in nature but not always in gemstone quality. Historically known locations are India and Sri Lanka (the area around Tatnaputi). Iridescent quartz from the Poona area in India and from Myanmar is a rarity. Beautiful crystals come from Kenya and Madagascar, as well as from Brazil (Minas Gerais), Goiás, Bahia, and French Guiana. In the USA, rock crystal is found in pegmatites, including in Maine (near Ausburn), New York, North Carolina, Arkansas (Crystal Peak), and California. Of particular significance are occurrences in the Alps. Rock crystals are found in Switzerland (for example, in Urim, where a 135 kg crystal was found in the area of the St. Gotthard and Grimsel), in Austria (in 1965, a nearly 1000 kg crystal was found in a cavity at the Großglockner). Rock crystals are also found in Germany, the Czech Republic, Poland, and France. In the collections of various museums, there are unique, cut rock crystals. The Smithsonian Institution in Washington owns a cut stone of 7000 ct and a crystal ball with a diameter of 33 cm and a weight of 48.5 kg; this one comes from Burma and was cut in China.