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Pakistan is one of the few locations where natural pink topaz is found, and pink topaz which was not mined in Pakistan may have been heat-treatment. In fact, many of today's popular topaz colors have been achieved by artificial means - see: "Topaz Color Enhancements" below. Topaz typically has high clarity and minimal inclusions which are visible to the naked eye, making the cut stones "eye clean." Topaz should be handled with care to avoid developing cleavage flaws or fractures, due to the crystal's perfect (easy) basal cleavage. The stone's cleavage plane is in a single direction that is perpendicular to the c-axis, with a conchoidal fracture, making topaz difficult to set without fracturing. Topaz PropertiesPure topaz is a transparent silicate or "nesosilicate" mineral created from a combination of aluminium and fluorine, and is typically found in association with acidic rocks such as granite or rhyolite. The fact that topaz has a relatively low refractive index, yet a high specific gravity, is fairly unique in the gem world.  The world's primary source for Sherry-colored gemmy topaz is in the region surrounding the colonial city of Ouro Prêto in Minas Gerais, Brazil. Within this region, topaz is found in conjunction with beryl (aquamarine) and quartz, associated with igneous rock pegmatite veins or dikes. Like beryl, topaz is the hardest silicate with a hardness of 8 on the Mohs scale. Topaz has a chain-like lattice structure of irregular octahedrons, and an elongate-prismatic dipyramidal crystal-habit that produces a crystal with orthorhombic pyramid faces, and multi-faceted terminations forming pinacoid domes. Topaz Crystallography, Chemistry, Physical Properties
Topaz Optical Properties
Imperial TopazImperial Topaz with its distinct peach, pink, or mauve hues is perhaps the rarest topaz variety, and the primary source is found at the Capão Imperial Topaz, Vermelháo, and Antonio Periera Mines in the town of Ouro Prêto, Minas Gerais, Brazil.
Imperial topaz, which is also known as "precious topaz," was named in honor of the Brazilian monarchy who prized its unusual and rich golden-sherry hue. The world's largest cut topaz is the "American Topaz," with a total weight of 22,892.50 carats (5,785 kg). The American Topaz originated from in Ouro Preto, Brazil, and it was cut in Idar-Oberstein, Germany over a period of two years. The giant topaz sphere resides at the Smithsonian Museum of Natural History in Washington DC.
 Topaz Color EnhancementsIrradiated & Heat-Treated 'Blue Topaz' Blue topaz is very rare in nature, and typically it has had a combination of gamma-ray irradiation via an electron-beam linear accelerator, followed by heat treatment at 180º C to 280º C to bring out its intense cobalt-blue color. Prior to treatment, so-called "blue topaz" typically starts out as a grayish-blue to silver-gray colored stone. The hue and intensity of blue topaz is categorized as: "London Blue" (blue-green), "Sky Blue" (light blue), "Swiss Blue" (medium to dark indigo blue), and "Maxi Blue" (deep and intense blue).  Orange-brown topaz is heat treated to 450 C in a process called "pinking" which is used to bring out a purplish-pink color. When yellow topaz is heat treated, it takes on a reddish-pink color. These treatments are permanent and do not affect the stone's durability or hardness. Vapor Color Coating Iridescent colors found in "mystic topaz" can be added to natural topaz by applying a thin layer of titanium oxide vapor (vapor color-coating) to the outside of the stone, but this vapor color-coating treatment is not permanent, and can wear off over time. Diffusion Topaz Treatment White, or clear topaz can be treated using the "Diffusion Topaz Treatment" which will create "Peacock Blue", "Sapphire Blue", "Apple Green", and "Emerald Green" topaz colors. This diffusion treatment is claimed to be more durable than the vapor color-coating mentioned above. Many of these enhancement treatment s are done in Sri Lanka. Another relatively new process in the topaz enhancement industry is the "Center-Fussed Colored Topaz" treatment.
Bibliography and Reference on Topaz Judith Crowe, The Jeweler's Directory of Gemstones The Mineralogical Record, A Mineral Collector's Knowledge Database Cally Hall, Smithsonian Gemstones Walter Schumann, Gemstones of the World Renee Newman, Gemstone Buying Guide Antoinette L . Matlins, Antonio C. Bonanno, Gem Identification Made Easy | Copyright © 2009 AllAboutGemstones.com. All rights reserved. | | | |||||||||||||||||||||||||||||||||||||||||||||||||
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: Topaz
