19 Mart 2013 Salı

Texas State Gemstone

Texas State Gemstone

Texas Blue Topaz

Topaz is a silicate mineral of aluminum and fluorine. Its crystals are mostly prismatic. Topaz is the hardest silicate mineral and, after corundum and diamond, the hardest mineral in nature.
Pure topaz is colorless and transparent to opaque. However, due to impurities, this stone occurs naturally in many colors, including white, yellow, orange, brown, gray, light blue, greenish blue, and green; rarely it is pink, purple, or deep blue. Almost all pink and purple topaz on the market, as well as much of the deep blue topaz, has been irradiated and heat-treated from colorless, pale yellow, gray, or brown stones. Topaz from certain localities may turn colorless upon heating. Mystic topaz is colorless topaz that has been coated to achieve the desired rainbow effect.
Texas blue topaz was designated the official state gemstone in 1969. This mineral is found in the Llano uplift area, especially west to northwest of Mason County. In 1977, Texas also recognized an official state gemstone cut, the lone star cut. Designed by two native Texans, the cut is in the shape of a five-pointed star for the Lone Star of Texas.
Utah designated topaz as its official state gem in 1969. 
The name for this gem comes from the Greek τοπάζιον (topazion), meaning "to seek," apparently in allusion to the island of Zabargad or Topasos in the Red Sea, Egypt. The island was an ancient source of peridot, which was once referred to as topaz. The name may also come from a Sanskrit word meaning fire.
Topaz occurs in pegmatites of granite, in high-temperature quartz veins, and in vapor cavities in rhyolite lava flows like those at Topaz Mountain in western Utah.
Because topaz is widespread, only a few localities producing the finest specimens are mentioned here.
  • Russia, near Mursinka, Ural Mountains; Adun-Chilon and Borshchovochnoii Mountains, Nerchinsk district, Siberia
  • Germany: Schneckenstein, Saxony
  • China: Xilingeleimeng, Inner Mongolia
  • Pakistan: Ghundao Hill, near Katlang, Mardan district; and Skardu and Gilgit districts
  • Myanmar: Mogok district
  • Japan: Tanokamiyama, Shiga Prefecture; and Naegi district, Gifu Prefecture
  • Brazil: Ouro Preto and Virgem da Lapa, Minas Gerais
  • United States: Devils Head, Douglas County, Colorado; Thomas Range, Juab County, Utah; Lord’s Hill, Stoneham, Oxford County, Maine; Baldface Mountain, Carroll County, New Hampshire; Ramona, San Diego County, California; Streeter, Mason County, Texas
  • Mexico: Tepetate, San Luis Potosi
  • Zimbabwe: St. Anne’s mine, Miami district
  • Namibia: Klein Spitzkopje
  • Mozambique: Alto Ligonha district
  • Nigeria: Jos district
The most famous topaz is a colorless stone that was originally thought to be a diamond. It is a 1,680-carat gem known as the Braganza Diamond and forms part of the Portuguese Crown Jewels. Another well-known topaz is in the Grünes Gewölbe, or the "Green Vault," in Dresden, Germany, which has one of the world’s most important gem collections. The Smithsonian Institution, the American Museum of Natural History in New York, and the British Museum all display numerous outstanding rough or cut topaz specimens.
All colors of topaz are fashioned into gemstones. The most valuable are those with pink to reddish tones and the yellow-brown or golden yellow variety, which are also called imperial because they were used in the jewelry of the 18th and 19th century Russian czarinas. The most common color is yellow with a red tint. The most popular and most affordable color is blue. Colorless topaz is sometimes cut as a brilliant to resemble diamond.
The beautiful colors, high luster, and well-formed and multifaceted crystals make topaz an important mineral specimen. Gem collectors particularly prize topaz in the matrix.
During the Middle Ages, topaz was thought to heal both physical and mental disorders and prevent death. Greeks believed it could make its wearer invisible, while the Romans believed it could improve eyesight. Egyptians believed topaz was the color of the mighty sun god Ra, and wore it to protect them from injury.
This gemstone is said to have a cooling effect. It is believed to dispel sadness and anger, and also to warn its wearer of poisons and sudden death. Legend has it that it improves eyesight.
Blue topaz is the traditional birthstone for those born in December. Orange or yellow topaz is the traditional November birthstone, and a symbol of friendship. Topaz is also the stone for the zodiac sign of Sagittarius and the suggested anniversary gemstone for the fourth, 19th, or 23rd year of marriage.

State Gemstone
Rough Sample of Topaz Embedded in Rock
State Gemstone
Hidden Topaz Crystal
State Gemstone
Glistening Blue Topaz Setting
Group: Silicate mineral
Chemical Formula: Al2SiO4(F,OH)2
Crystal Structure:  Orthorhombic
Hardness (Mohs): 8
Color: Clear (if no impurities), blue, brown, orange, gray, yellow, green, pink and reddish pink.
Transparency: Transparent, Translucent
Luster: vitreous
Birefringence: δ = 0.010
Pleochroism: Weak in thick sections
Refractive Index: nα = 1.606–1.629
nβ = 1.609–1.631
nγ = 1.616–1.638
Density: 3.49–3.57
Streak: White
Cleavage: [001] Perfect
Fracture: Conchoidal

Some data courtesy of the Mineralogical Society of America
Author: World Trade Press

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