Description
Tourmaline (quartz) is a group of minerals, all cyclosilicates. The minerals in this group share a characteristic chemical formula: AX3Y6(BO3)3 Si6O18(O, OH, F)4. The A can contain calcium or sodium. The X can be aluminum, iron, lithium, or magnesium. The Y is normally aluminum, but can also be chromium or iron. Some potassium can exist in the A position, manganese can be in the X, and vanadium can be found in the Y, but these elements are not commonly found in tourmaline group formulas. Tourmaline occurs in pegmatites, metamorphites, magmatites, and alluvial deposits. Although tourmaline was known in the Mediterranean region since ancient times, it was not introduced into Western Europe from Sri Lanka by the Dutch until 1703. They named the new gemstone with a Sinhalese word “Turmali,” meaning “stone of mixed colors.” Rubellites were traditionally used as gemstones – they were used by artists as talismans, believed to enhance their creative powers. Tourmalines have certain unique properties. They are piezoelectric, meaning that when a crystal is heated or compressed, different electrical charges are formed at both ends of the crystal. This creates an electrical potential. When an external electrical potential is applied to the crystal, it vibrates. The minerals are pleochroic, meaning that the crystal appears darker in color when viewed along its longest axis than when viewed perpendicular to that axis. The four best-known and most common tourmaline minerals have varying colors and transparencies. Elbaite is transparent and a valuable gemstone. Schorl, rich in iron, is the most common mineral in the tourmaline group and is black and opaque. It is primarily formed in pegmatites, the outermost, slowly cooling gangues of magma. The two other frequently encountered tourmalines are dravite and uvite. Dravite is typically translucent brown and can grow very large. Uvite is green translucent to opaque. Tourmaline occurs in the sand fraction of Dutch Quaternary river sediments. It is a characteristic component of Meuse sands, among other things. In the heavy mineral analysis conducted in the Netherlands by the National Geological Survey during the second half of the twentieth century, the mineral is classified in the so-called stable group
Gemstone therapy Black tourmaline
Rock crystal is the colorless and most common variety of the mineral quartz (silicon dioxide, SiO2). The name "rock crystal" is derived from the Greek word "krustallos," meaning ice. It was believed that rock crystal was ice shaped by the gods. Rock crystal was already known during the Mesolithic period. During the Roman period, it was brought from the Alps under the name "petrified ice." Theofratus called it "krystallos." Pliny the Elder also mentions it. The name "quartz" was introduced in 1529 by Georgius Agricola. Eastern peoples considered rock crystal 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 discolor when they came into contact with poison. Thus, the chain became an amulet that protected the king. Compare the Rudolphinian imperial crown and the chain of the Jehovah's Witnesses. Origin: Megnathites, pegmatites, hydrothermal and alpine veins, alluvial deposits. Occurrence: Rock crystal is widespread in nature, but not always in gem quality. Historically known sources are India and Sri Lanka (the Tatnaputi area). Iridescent quartz from the Poona region in India and Myanmar is rare. Beautiful crystals come from Kenya and Madagascar, as well as Brazil (Minas Gerais). Goisas, Bahia, and French Guiana. In the United States, rock crystal occurs 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, near Urim, where a 135 kg crystal was found in the area of St. Gotthard and Grimsel), and in Austria (in 1965, a crystal weighing almost 1000 kg was found in a cavity near the Grossglockner). Rock crystals are also found in Germany, the Czech Republic, Poland, and France. Unique cut rock crystals are held in the collections of various museums. The Smithsonian Institution, Washington, owns a 7000-carat cut stone and a spherical rock crystal with a diameter of 33 cm and a weight of 48.5 kg; this one originates from Burma and was cut in China.
