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Topaz Gemstone Information

The name topaz is thought to have come from the Red Sea island formally known as Topazos in Greek (renamed Zebirget and also known as St. John's Island).

Although abundant on the market as mainly blue stones (produced by heat-treating natural colourless topaz) some naturally coloured topaz is prized and considered precious. Stones of particular interest to the market are natural red to pink topaz (the most valuable) and Imperial Topaz, a natural golden yellow to orange coloured topaz. The price of precious topaz has elevated over the years and many are now purchased for investment.

Colourless material is readily available, it was once used as a diamond simulant before the event of high quality simulants such as cubic zirconia.

Heat treated and irradiated blue stones are marketed as Sky Blue (light blue), Swiss Blue (medium blue) and London Blue (darker blue).

There is now an abundance of fancy topaz on the market, in all imaginable colours, some are surface diffused and others are coated to apply a colour. Mystic topaz is colourless material coated to display a rainbow of colours.

Source locations for topaz include: Africa, Afghanistan, Australia, Brazil, China, Japan, Madagascar, Mexico, Myanmar (Burma), Pakistan, Russia, Sri Lanka, UK and the USA.

Physical Properties

Stone type:
Topaz.
Crystal System:
Orthorhombic.
Chemical Composition:
Fluosilicate of aluminium with hydroxyl. Al2(F,OH)2SiO4.
Colour:
Colourless, yellow, light-blue, light-green, pink-to-red, red-brown. Many fancy colours are produced commercially.
Lustre:
Vitreous.
Pleochroism:
Trichroic: Shows varying depth of body colour.
Dispersion:
Low.
Hardness:
8 on the Mohs' scale of hardness.
Toughness:
Poor: Due to a perfect cleavage topaz is susceptible to chipping and cracking when knocked or put under pressure.
Cleavage:
Perfect.
Density in gm/cc:
3.50 to 3.57
Double refraction:
Yes.
Refractive index:
1.609-1.643

Common Treatments

Blue topaz is produced by irradiating and heat-treating colourless material.

Green stones are also produced by lattice diffusion methods.

Mystic topaz is manufactured by depositing a thin layer of titanium onto the pavilion facets of a cut stone, by using a method called physical vapour deposition. The stone then displays iridescent colours.


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