ColorlessTopaz

 

As a mineral, this is far and away the most common variety. of transparent topaz, although it is of limited importance as gemstone. All colorless gemstones compare most unfavorably with diamond, their lower refractive indices an lesser dispersion making them far less attractive. Topaz has the advantage over the others of being found in large stones and great quantities, and of having good hardness and luster. Therefore it is of some interest to hobbyists.

Appearance Gemstones are generally free, or almost sc of inclusions because they can be culled from the large quantities available; but they may show signs of extensive internal cleavage. In large stones (of a few centimeters) the mineral's weak birefringence can be detected with the a of a lens, the facet edges appearing double when see through a flat facet of the stone. The stones easily acquire good luster and are only disappointing on the rare occasions when they are given the brilliant cut, prompting comparison with diamonds, which have a very different lust, and fire.


Distinctive features Colorless topaz differs little from the colorless varieties of other minor gems, which, with the exception of quartz, are all much rarer. Incipient cleavage where present, may be a distinguishing feature. If the edges appear double, denoting birefringence, this can distinguish it from synthetic colorless spinel, which has a sir large density; but it cannot differentiate it from other min gemstones such as colorless beryl, tourmaline, and corundum. To distinguish it with any certainty from these, the refractive indices must be determined.


Occurrence It is found in various parts of Brazil, the Soviet Union, the United States, Germany (Saxony), a Japan. Africa, too, has a plentiful supply of colorless topaz in the tin-mining areas of both Nigeria and Zaire. It is also found in Namibia.

Value One of the lowest for transparent gemstones, even though it is greatly appreciated by amateur cutters as a raw material. Apparently, it is being used increasingly for the production of blue topaz by means of irradiation.


Simulants and synthetics It is neither imitated nor produced synthetically

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