Utah State Gemstone
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, is one of the hardest minerals in nature.
Pure topaz is colorless and transparent to opaque. However impurities cause this stone to occur naturally in many colors, including white, yellow, orange, brown, gray, light blue, greenish blue, and green, and is rarely 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.
Utah designated topaz as the official state gem in 1969. It is a semiprecious gem found in Beaver, Juab, and Tooele Counties. Small, perfect crystals are found in the Thomas Mountain Range in Juab County, Utah, which is a very popular area for rock collectors.
Blue topaz is the official gemstone for the state of Texas.
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."
FORMATION AND OCCURRENCE
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.
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.
Orange or yellow topaz is the traditional November birthstone, and a symbol of friendship. Blue topaz is the traditional birthstone for those born in December. 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.
SUBSTITUTES / SYNTHETICS
Citrine, a yellow-brown variety of quartz, closely resembles yellow-brown topaz. Unfortunately, unscrupulous dealers have created false names for citrine and sell it to buyers who think they are purchasing the more expensive and more valuable topaz. Much of the "topaz" labeled with a prefix name (such as gold topaz, Madeira topaz, false topaz, Brazilian topaz, bahia topaz, star topaz, Oriental topaz, Indian topaz, and citrine topaz) is actually heat-treated citrine. Exceptions to this are the gem varieties of topaz: imperial topaz, pink topaz, blue topaz, silver topaz (colorless), brown topaz, green topaz, Sherry topaz, London blue topaz (the deepest blue form of topaz), Swiss blue topaz, and Paraiba topaz.
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, sometimes opaque
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
Cleavage:  Perfect
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press