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Topaz

Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2 Si O4( F, OH)2. Topaz crystallizes in the orthorhombic system, and its crystals are mostly prismatic terminated by pyramidal and other faces. It is one of the hardest naturally occurring minerals ( Mohs hardness of 8) and is the hardest of any silicate (i.e., silicon-based) mineral. This hardness combined with its usual transparency and variety of colors means that it has acquired wide use in jewellery as a cut gemstone as well as for intaglios and other gemstone carvings.

Characteristics

Topaz in its natural state is a golden brown to yellow, a characteristic which means it is sometimes confused with the less valuable gemstone citrine. A variety of impurities and treatments may make topaz wine red, pale gray, reddish-orange, pale green, or pink (rare), and opaque to translucent/transparent. The pink and red varieties come from chromium replacing aluminum in its crystalline structure. Orange topaz, also known as precious topaz, is the traditional November birthstone, the symbol of friendship, and the state gemstone of the US state of Utah. Utah State Gem – Topaz. Pioneer.utah.gov (2010-06-16). Retrieved on 2011-10-29. Imperial topaz is yellow, pink (rare, if natural) or pink-orange. Brazilian Imperial Topaz can often have a bright yellow to deep golden brown hue, sometimes even violet. Many brown or pale topazes are treated to make them bright yellow, gold, pink or violet colored. Some imperial topaz stones can fade on exposure to sunlight for an extended period of time. Imperial Topaz, Natural History Museum of Los Angeles County Gemstones & Gemology – Topaz, Emporia State University Blue topaz is the state gemstone of the US state of Texas. State Gem – Texas Blue Topaz. State Gemstone Cut – Lone Star Cut. state.tx.us Naturally occurring blue topaz is quite rare. Typically, colorless, gray or pale yellow and blue material is heat treated and irradiated to produce a more desired darker blue. Mystic topaz is colorless topaz which has been artificially coated via a vapor deposition process giving it a rainbow effect on its surface. Mystic Topaz, Consumer Information. Farlang.com (2008-10-30). Retrieved on 2011-10-29. Although very hard, topaz must be treated with greater care than some other minerals of similar hardness (such as corundum) because of a weakness of atomic bonding of the stone's molecules along one or another axial plane (whereas diamonds, for example, are composed of carbon atoms bonded to each other with equal strength along all of its planes). This gives topaz a tendency to fracture along such a plane if struck with sufficient force. Topaz has a relatively low index of refraction for a gemstone, and so stones with large facets or tables do not sparkle as readily as stones cut from minerals with higher refraction indices, though quality colorless topaz sparkles and shows more "life" than similarly cut quartz. When given a typical "brilliant" cut, topaz may either show a sparkling table facet surrounded by dead-looking crown facets or a ring of sparkling crown facets with a dull well-like table.

Localities and occurrence

Topaz is commonly associated with silicic igneous rocks of the granite and rhyolite type. It typically crystallizes in granitic pegmatites or in vapor cavities in rhyolite lava flows including those at Topaz Mountain in western Utah and Chivinar in South America. It can be found with fluorite and cassiterite in various areas including the Ural and Ilmen mountains of Russia, in Afghanistan, Sri Lanka, Czech Republic, Germany, Norway, Pakistan, Italy, Sweden, Japan, Brazil, Mexico; Flinders Island, Australia; Nigeria and the United States. Brazil is one of the largest producers of topaz, some clear topaz crystals from Brazilian pegmatites can reach boulder size and weigh hundreds of pounds. Crystals of this size may be seen in museum collections. The Topaz of Aurangzeb, observed by Jean Baptiste Tavernier weighed 157.75 carats. Famous and Notheworthy Topazes Rao Bahadur, A Handbook of Precious Stones, Geological Survey of India The American Golden Topaz, a more recent gem, weighed a massive 22,892.5 carats. Large, vivid blue topaz specimens from the St. Anns mine in Zimbabwe were found in the late 1980s. Colorless and light-blue varieties of topaz are found in Precambrian granite in Mason County, Texas Handbook of Texas Online – Mineral Resources and Mining. Tshaonline.org. Retrieved on 2011-10-29. within the Llano Uplift. There is no commercial mining of topaz in that area. Mason, Texas Chamber of Commerce Web site File:TopazMountainByPhilKonstantin.jpg| Topaz Mountain, Utah File:Topaz-k312b.jpg|Sherry-colored topaz from Maynard's Claim (Pismire Knolls), Thomas Range, Juab County, Utah, USA File:Topaz-k-182a.jpg|Blue Topaz from Erongo Mountain, Usakos and Omaruru Districts, Erongo Region, Namibia File:Topaz-200562.jpg|Red topaz from Tepetate, Municipio de Villa de Arriaga, San Luis Potosí, Mexico

Etymology

The name "topaz" is usually derived (via Old French: Topace and Latin: Topazus) from the Greek Τοπάζιος (Τοpáziοs) or Τοπάζιον (Τοpáziοn), from Τοπαζος, the ancient name of St. John's Island in the Red Sea which was difficult to find and from which a yellow stone (now believed to be chrysolite: yellowish olivine) was mined in ancient times; topaz itself (rather than topazios) was not really known before the classical era. Pliny said that Topazos is a legendary island in the Red Sea and the mineral "topaz" was first mined there. Alternatively, the word topaz may be related to the Sanskrit word तपस् "tapas", meaning "heat" or "fire".

Historical usage

Nicols, the author of one of the first systematic treatises on minerals and gemstones, dedicated two chapters to the topic in 1652.A Lapidary or History of Gemstones, University of Cambridge, 1652. In the Middle Ages, the name topaz was used to refer to any yellow gemstone, but in modern times it denotes only the silicate described above. Many modern English translations of the Bible, including the King James Version mention topaz. However, because these translations as topaz all derive from the Septuagint translation topazi os, which as mentioned above referred to a yellow stone that was not topaz, but probably chrysolite ( chrysoberyl or peridot), it should be borne in mind that topaz is likely not meant here.Farrington, Oliver (1903) Gems and Gem Minerals. Chicago. p. 119. The masoretic text (the Hebrew on which most modern Protestant Bible translations of the Old Testament are based) has pitdah as the gem the stone is made from; some scholars think it is related to an Assyrian word meaning "flashed". More likely, "pitdah" is derived from Sanskrit words ( pit = yellow, dah = burn), meaning "yellow burn" or, metaphorically, "fiery".

Superstition

An English superstition held that topaz cured lunacy.Pettigrew, Thomas Joseph (1844) On Superstitions Connected with the History and Practice of Medicine and Surgery. Philadelphia E. Barrington and G.D. Haswell. p. 70.

References

External links

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This article based upon the http://en.wikipedia.org/wiki/Topaz, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Topaz&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany