11 Ekim 2013 Cuma

Nevada State Gemstones

Nevada State Gemstones

Black Fire Opal

Official precious gemstone
Opal is not a true mineral in the accepted sense of the word because it does not have a crystal structure. Considered a mineraloid gel, opal is a hydrated silicon dioxide. The stone's base color can be white, yellow, orange, red, purple, blue, green, gray, brown, black, or colorless. White and shades of green are the most common, while red against a black background is the rarest. Certain specimens display exceptional variations in color or iridescent flashes of color when turned or viewed from different directions. This phenomenon is called "play of color."
Opal has over one hundred variety and trade names, but the list of accepted or commonly used names is much shorter. The most important and most widely known opal is the precious opal, whose play of color phenomenon makes it valuable. Fine specimens of precious opal with intense play of color can be worth more than diamond. The density and pattern of the silica spheres that compose precious opals are arranged in such a way that when light is diffracted through the stone, it causes a color sheen.
Precious opal may be subdivided further by color modifiers that describe the body color, such as white, black, pink, and blue. Opals not exhibiting play of color are called common opals, and are much less valuable. This milky appearance of a common opal is called opalescence.
Opal is brittle, heat sensitive, and breaks and scratches easily. It can develop internal and external cracks if it is dried too quickly or exposed to heat over a long period of time. The stone is three to 30 percent water, and some varieties self-destruct through the loss of water. Despite these drawbacks, opal's unsurpassed beauty guarantees its status as a premier gemstone.
State Symbol
Black fire opal was adopted as the official precious gemstone of Nevada in 1987. In 1917, Nevada's Rainbow Ridge Mine produced the Roebling Opal, weighing 2,265 carats. The stone was donated to the Smithsonian and is displayed in the National Gem Collection. The world's largest opal, weighing 7 pounds (3.18 kg), was also found at the Rainbow Ridge Mine. Another Nevada gem in the Smithsonian collection is a 169-carat black opal from the Royal Peacock opal mine. Both of these mines are located in the Virgin Valley in northwest Nevada, the only U.S. state to produce black fire opal in significant quantities.
Name Origin
Reportedly, opal's name evolved from the Roman word opalus from the Greek word opallios, meaning, "to see a change of color." The Greek word was a modification of the ancient Sanskrit name for opal, upala, which means, "precious stone."
Formation and Occurrence
Opal is deposited at relatively low temperatures and may occur in the fissures of almost any kind of rock. It is most commonly found with limonite, sandstone, rhyolite, marl, and basalt.
Famous Examples
Some 90 to 95 percent of the world's opal comes from the Australian outback, and this part of the world has produced some stunning specimens. The Olympic Australis opal is reported to be the largest and most valuable uncut gem opal ever found. It weighs 17,000 carats and was found in 1956 at the famous Eight Mile opal field in Coober Pedy, South Australia. The Aurora Australis Opal was found at Lightning Ridge, New South Wales, Australia, in 1938. At 180 carats, it is considered to be the world's most valuable black opal. Because of its abundant deposits of white and black precious opal, Australia designated opal its national gemstone.
Geographic Distribution of Opal

  • Algeria
  • Antarctica
  • Argentina
  • Australia
  • Austria
  • Bolivia
  • Brazil
  • Bulgaria
  • Canada
  • Chile
  • China
  • Colombia
  • Cuba
  • Czech Republic
  • DR Congo
  • Denmark
  • Ecuador
  • Egypt
  • Ethiopia
  • Fiji
  • Finland
  • France
  • Germany
  • Greece
  • Greenland
  • Honduras
  • Hungary
  • Iceland
  • India
  • Indonesia
  • Israel
  • Italy
  • Japan
  • Kazakhstan
  • Kenya
  • Madagascar
  • Malaysia
  • Mali
  • Mars
  • Mexico
  • Morocco
  • Namibia
  • New Zealand
  • Norway
  • Oman
  • Papua New Guinea
  • Paraguay
  • Peru
  • Poland
  • Portugal
  • Reunion Island
  • Romania
  • Russia
  • Saudi Arabia
  • Slovakia
  • Somaliland
  • South Africa
  • South Korea
  • Spain
  • Sweden
  • Switzerland
  • Tanzania
  • Thailand
  • Turkey
  • United Kingdom
  • Ukraine
  • United States
  • Uzbekistan
  • Vanuatu
  • Venezuela
  • Atlantic, Pacific, and Indian Oceans

Opal has centuries of history as a treasured gemstone. Historically, beliefs associated with the wearing of opal have varied. Early Greeks thought that opals gave their owners the powers of foresight and prophecy, and Romans adored it as a token of hope and purity. Eastern people regarded it as sacred, and Arabs believed it fell from heaven. Australian aboriginal legend says that opals were born at the spot where the creator came to earth on a rainbow in order to bring peace to humans.
In the Middle Ages, opal was thought to possess all the characteristics of all the gemstones represented by the many colors of opals, and therefore to provide great luck. In the 19th century, superstitions grew about the bad luck or fate that could befall one for wearing opal if it were not the wearer's birthstone. Today, these superstitions have diminished, but some people still believe it is bad luck to wear opals. Opal reached a height of popularity in the Art Deco period.
Precious opal is the primary gem form of this stone, but gems are cut from common opal as well. Opal is most commonly cut into cabochons and used in all types of jewelry. The most desired variety of opal is the black opal, which has a dark green, dark blue, or black background. Also important is white opal with its white-, yellow-, or cream-colored background. Mexican fire opal is yellow-orange to red, transparent to translucent, and opalescent. When Mexican fire opal displays play of color, it is called precious fire opal. Fire opal is the second most important opal commercially.
Opal is thought to have healing powers, including relieving depression and improving eyesight. It is also said to help one find inner beauty and true love.
Opal is considered the birthstone for people born in October or under the zodiac signs of Libra and Aquarius. It is the mystical birthstone for April and the gemstone for the 14th and 18th years of marriage.
Substitutes / Synthetics
Following the discovery of the ordered sphere structure of precious opal, a synthetic opal trade began. Imitation opal can be distinguished from genuine opal as it does not fluoresce under UV light, is more porous, and has regular patches of color. Some imitation opals are made of glass or plastic.
State Gemstone
Black Fire Opal
State Gemstone
Close-up of Black Fire Opal
Group: Silicate
Chemical Formula:SiO2·nH2O
Crystal Structure: Irregular veins, in masses, in nodules
Hardness (Mohs): 5.5-6.5
Color: White, black, red, orange, most of the full spectrum, colorless, iridescent
Transparency: Transparent, opaque
Luster: Vitreous, waxy, greasy, dull
Birefringence: None
Pleochroism: None
Refractive Index: 1.450 (+.020, -.080) Mexican opal may read as low as 1.37, but typically reads 1.42-1.43
Density: 2.15 (+.08, -.90)
Streak: White
Cleavage: None
Fracture: Conchoidal to uneven
Data Source:


Offical semiprecious gemstone
Turquoise is an opaque mineral, a hydrated phosphate of copper and aluminum. It is also formed by the percolating action of meteoric waters, usually in arid regions or deserts, on aluminous igneous or sedimentary rocks.
Turquoise comes in various shades of blue, blue-green, green-blue, green, yellow-green, and yellow. The material can be solid colored or spider-webbed in any of these different colors or shades. The quality varies from hard, solid material that takes a good polish, to soft porous material that can only be used as feed stock for treatment, enhancement, or stabilization processes.
State Symbol
Nevada has been a major producer of turquoise since the 1930s, and until the early 1980s, was the largest producer in the United States. It is estimated that over the years, 75 to 100 different mines in the state produced sizable quantities of turquoise. Production varied from a few thousand dollars worth of material at some of the properties to more than a million dollars at others. To date, total production of rough turquoise is estimated to be in the range of $40 to $50 million. Nevada designated turquoise its official state semiprecious gemstone on May 27, 1987.
Name Origin
The name turquoise is antiquated French for "Turkish," because at one time, turquoise came to France from Turkey. The stone was apparently also referred to as "turquin," another old term meaning "Turk." However, the turquoise in question most likely originated in Alimersai Mountain in Persia (now Iran) or the Sinai Peninsula in Egypt, two of the world's oldest known turquoise mining areas. The unique color of the stone has led to its use to describe anything similarly colored.
Geographic Distribution of Turquoise
Turquoise was one of the first minerals to be mined, and continues to be mined mostly by hand. Egyptians mined and used turquoise from the Sinai Peninsula about 3,000 years ago, and six mines remain in the region.
An area near Neyshabur, Iran, has been mined for over 2,000 years and continues to supply some of the world's finest turquoise. For thousands of years, the finest intense blue turquoise in the world was found in Persia, and the term "Persian turquoise" became synonymous with the finest quality. This changed during the late 1800s and early 1900s when modern miners discovered or rediscovered significant deposits of high-quality turquoise in the western and southwestern United States. Material from many of these deposits was just as fine as the finest Persian turquoise. Today, Persian turquoise more often describes the stone's quality than its origin, and the majority of the world's finest-quality turquoise comes from the United States, the largest producer of turquoise.
Until the 1920s, New Mexico was the United States' largest producer of turquoise. Currently, with the exception of byproduct material from copper mines, production of turquoise from deposits in New Mexico, for all practical purposes, has stopped. Turquoise still can be found in New Mexico, but Arizona and Nevada have surpassed it in terms of both annual and total production.
Turquoise is one of the oldest gemstones known. Pharoahs, Aztec kings, and the people of Persia, Mesopotamia, and the Indus Valley civilization adorned themselves with turquoise jewelry.
Since about 200 BCE, turquoise has been extensively used by both southwestern U.S. Native Americans and by many indigenous tribes in Mexico. The popular Native American jewelry with turquoise mounted in silver is relatively new. Some believe this style of jewelry was unknown prior to about 1880, when a white trader persuaded a Navajo craftsman to make turquoise and silver jewelry using coin silver. Prior to this time, Native Americans made solid turquoise beads, carvings, and inlaid mosaics.
China and Tibet are minor sources of the mineral. Sacred to Tibetans, turquoise is often used by shamans in rituals and ceremonies. It is believed to promote mental and spiritual clarity and expansion, as well as enhance wisdom, kindness, trust, and understanding.
Turquoise is the astrological birthstone for Taurus and Sagittarius, the planetary stone for Aquarius, and one of four modern birthstones for December. It is also the Russian and Polish birthstone for December, and the fifth and 11th wedding anniversary stone. It is one of the most valuable nontransparent minerals used in jewelry.
Substitutes / Synthetics
Egyptians were the first to produce artificial turquoise, which was used in glazed earthenware. The most common imitation of turquoise encountered today is dyed howlite and magnesite, both white in their natural states. Howlite also has the natural (and convincing) advantage of black veining similar to that of turquoise. Dyed chalcedony, jasper, and marble are less common, and much less convincing.
Two other gem materials that can resemble certain colors and shades of turquoise but are separate mineral species are variscite and faustite. Both have been mistaken for and marketed as turquoise. Attractive gemstones can be cut from both variscite and faustite, and therefore would be noteworthy as gem materials on their own.
State Semiprecious Gemstone
Turquoise Stone
State Semiprecious Gemstone
Meticulous Turquoise Medallion
State Semiprecious Gemstone
Raw Sample of Turquoise
Group: Turquoise
Chemical Formula: CuAl6(PO4)4(OH)(H2O)
Crystal Structure: Triclinic
Hardness (Mohs): 5-6
Color: Bright blue, sky-blue, pale green, blue-green, turquoise-blue, apple-green, green-gray
Transparency: Transparent, translucent, opaque
Luster: Vitreous, waxy, dull
Birefringence: +0.040
Pleochroism: Weak
Refractive Index: ná = 1.610 nâ = 1.615 nã = 1.650
Density: 2.6-2.8 g/cm3
Streak: Pale greenish blue to white
Cleavage: Perfect
on {001}, good on {010}
Fracture: Conchoidal
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press

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