Topaz
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 stone.
Colourless material is readily available, it was once used as a diamond simulant.
Source locations for topaz include: Africa, Afghanistan, Australia, Brazil, China, Japan, Madagascar, Mexico, Myanmar (Burma), Pakistan, Russia, Sri Lanka, UK and the USA.
Properties of the Gemstone and Additional Information
| Gemstone 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 |
| Lustre: | Vitreous |
| Pleochroism: | Trichroic: Shows varying depth of body colour. |
| Dispersion: | Low |
| Hardness: | 8 on the Mohs' scale |
| 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. Stones are marketed under names such as Sky blue, Swiss blue and London blue topaz.
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.