Description
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.
Hematite (from Greek: αιμία, haima, blood) is a mineral composed primarily of ferric oxide crystals (iron(III) oxide, Fe2O3), one of the iron oxides. It occurs alongside other varieties such as red bloodstone and grayish-black to black iron luster and micaceous iron. The mineral has a hardness of between 5 and 6. The so-called streak, or streak color, the color the mineral imparts when rubbed over an unglazed porcelain dish, is usually a characteristic blood red—from which the mineral derives its name. The mineral may contain traces of magnesium, manganese, and titanium. Hematite occurs both as a gangue mineral and in sedimentary layers. It is often the cause of the red coloration of many rocks. Other iron ores such as magnetite, limonite, and iron spar often occur alongside hematite. When magnetite has been converted to hematite, it is called martite. The mineral is found worldwide. In Europe, it is found in Germany, among other places, in the Lahn region, where the world's largest concentration of iron ore is located; in the Eifel, the Harz mountains, and the Thuringian Forest. It is also found in England in Cumberland and North Lancashire; in Belgium in Vezin and Namur; on the Italian island of Elba; and in Spain. In Africa, Algeria is a notable producer; and in the United States, it is found near Upper Lake and the Missouri River. More than half of the world's production currently comes from China, Brazil, and Australia. The mineral is also found in high concentrations on the surface of Mars, giving the "Red Planet" its characteristic orange-red color. Hematite mining is one of humanity's earliest mining activities: the powdery mineral has been found in graves dating back approximately 80,000 years. Quarries dating back to the Paleolithic period are known on the Greek island of Thasos, as well as at Rydno in Poland and Lovas in Hungary. Traces of prehistoric mining on a similar scale have also been found in Germany near Bad Sulzburg and in the Münster Valley, dating from around 5000 BC. These can be attributed to the Banded Pottery culture of the Upper Rhine. The Etruscans were already aware of the abundant presence of iron oxide on the island of Elba.
