Blue Topazo : What is it?
| Blue topaz ( Al2(F,OH)2SiO4) is a fluorosilicate of aluminum characterized by a naturally or synthetically induced blue color. Natural blue topaz is rare. Those that are sold in the market are mostly colorless topaz treated to develop a bluish color.
In the United States, blue topaz is currently the biggest selling “nontraditional” colored stone because it is more affordable compared to other blue gemstones like sapphire and aquamarine. The demand for blue topaz has led to the widespread treatment of colorless or pale blue Brazilian topaz to a darker blue color. The dark blue color is usually produced by irradiation and heating.
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Kinds of Blue Topazos include the following: |
Natural blue topaz
- Natural blue topaz is found in certain silicic volcanic rocks and in pegmatites.
- It is pale blue in color, sometimes almost colorless.
- It contains higher concentrations of fluorine than yellow or pink topaz that causes variations in its physical and optical properties.
- It has a color center that allows it to change color easily.
- A pale blue natural topaz can easily be darkened through irradiation and heating.
Treated blue topaz
- Treated colorless or pale blue topaz is irradiated and heated to develop a darker shade.
- The darker color is permanent and will not fade even in prolonged exposure to sunlight.
- Different methods are used for treating topaz to enhance their color; however, there is no definitive way to differentiate treated stones though the various methods employed.
- Some examples of the treatment methods used include: exposure to gamma ray source, exposure to high electron beam, exposure to fast neutrons (nuclear reactors), and treatment combining linear reactor, nuclear reactor, and heating.
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Quality: Choose a blue topaz with minimum inclusions as possible to make them more valuable.
Transparency: Choose a transparent blue topaz to make it shine brilliantly under the light.
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