|Topaz is a silicate fluorine aluminium silicate mineral available in a broad range of colors including yellow, yellow-brown, honey-yellow, flax, brown, green, blue, light blue, red, pink and colorless. It is formed by fluorine-bearing vapours given off during the last stages of the crystallization of igneous rocks. It typically occurs in cavities in rhyolites and granite and in pegmatite dikes, and in high-temperature veins. Often associated with cassiterite, topaz may be useful to indicate the presence of that tin ore.|
|Color Key:||colorless, blue, yellow-brown, pinkish orange, red-orange, red-brown, tan.|
|Refractive Index:||1.629 - 1.637|
|Density:||3.52 - 3.56|
|Ocurrence:||Brazil, Sri Lanka, Nigeria, Germany, Australia, Japan, Russia, Australia, Ireland, Zimbabwe.|
|Topaz has been known for at least 2000 years and is one of the gemstones which form the foundations of the twelve gates to the Holy City of the New Jerusalem.|
The finest British topaz is found in the Cairngorm Mountains in the Central Highlands, especially at Ben a Buird, Scot. The famous topaz rock of the Schneckenstein, in Germany, yields pale yellow crystals that were formerly cut for jewelry. Fine topaz occurs at several localities in the Urals and in Siberia, Russia, and beautiful crystals come from Takayama and Tanokamiyama in Japan. Brazil is a famous locality, the well-known sherry-yellow crystals coming from Ouro Preto, Minas Gerais, where they occur in a kaolinitic matrix. In the United States fine topaz has been worked near Pikes Peak, Colo., and in San Diego county, Calif. Common topaz occurs in coarse crystals at many localities. For detailed physical properties, see silicate mineral (table).
Pure topaz may be colourless and, when brilliant-cut, has been mistaken for diamond. It may also be coloured various shades of yellow, blue, or brown; the colour in many cases is unstable, and the brown topazes of Siberia are particularly liable to be bleached by sunlight. In 1750 a Parisian jeweler discovered that the yellow Brazilian topaz becomes pink on exposure to a moderate heat, and this treatment has since been extensively applied, so that nearly all the pink topaz occurring in jewelry has been heat-treated. Such "burnt topaz" is often known as Brazilian ruby, as is the very rare, natural red topaz. Cut topazes of large size are known, and it is said that the great "Braganza diamond" of Portugal is probably a topaz.
Although most topaz is naturally white or light yellow, it is commonly irradiated to produce the popular sky or swiss blue colors. Because of its good clarity and easy availability in large and calibrated sizes at very affordable prices, blue topaz will be a very popular gemstone.
| || || || || || |