Gem-A gemmology tutor, Lily Faber FGA EG, takes a look at topaz, the beautiful and warming birthstone of November, guaranteed to brighten up this chilly month of winter.
For those born in November, and to those born in other months, topaz is a well-known and hopefully well-loved gemstone.
The name topaz most likely originated from the Sanskrit word 'tapas', meaning 'fire'. This gemstone is thought to promote creativity, increase sensitivity to taste to enhance your dining experiences, boost mental clarity and to uncover lies and illusions. The ancient Greeks believed that topaz could render the wearer invisible - though I have yet to see proof of this effect! Topaz is the state stone for Texas and Utah in the United States of America, and is the talisman for the astrological sign Sagittarius.
Blue topaz with incipient cleavage seen under table. Photo courtesy of Lily Faber.
Colours and Localities
Most often associated with the colours yellow, orange, blue or pink, topaz can also be colourless, green and brown. One of the most valued colours is known as 'Imperial Topaz', which is pinkish-orange to red-orange. Another highly valued colour is 'sherry topaz', which is brownish-yellow to orange or yellow-brown.
Striated topaz crystal with iridescence due to internal fractures. Photo courtesy of Lily Faber.
Topaz can be found in Brazil, Russia, Pakistan, Mexico, the USA, Madagascar and Sri Lanka. In the 19th century, the main source for pink topaz was in the Ural Mountains in Russia. The imperial family, including the tsars, reserved exclusive rights to own and wear the colour, this imparting the name 'Imperial topaz'. It is less common than other naturally occurring colours of topaz, and is thought to resemble the colours of the setting sun.
Treated and coated topaz stones to bring out the blue colour. Photo by Pat Daly ©Gem-A.
Historically, all yellow stones were called topaz, which has since been corrected, for the most part. In some shops, misnomers can still be seen today. Names such as 'quartz topaz', 'Scotch topaz' or 'Spanish topaz' are a few names used for citrine quartz that are misleading, so don't fall for it!
It should be noted that almost all pink topaz on the market today is mined in Brazil and heat-treated to bring out the pink colour. Natural blue topaz is typically pale, and stronger colours like 'London blue' or 'Swiss blue' are achieved by irradiating and heating a colourless topaz to promote and stabilize the blue colour. One colour that was not created by nature is known as 'mystic' topaz. It is a colourless topaz that has been coated with a thin metallic layer to produce extreme iridescence.
Treated and coated topaz to display a range of pink and purple colour. Photo by Pat Daly ©Gem-A.
A range of treated and coated topaz stones displaying a myriad of colours. Photo by Pat Daly ©Gem-A.
Properties and Inclusions for topaz
Topaz is a relatively hard material, with a level of 8 on the Mohs scale of hardness. While it can take a high polish and show a bright vitreous lustre, its perfect and easy cleavage lets it down. Cleavage is a directional breakage that occurs along a crystal plane in only crystalline materials. Topaz has what is called 'basal' cleavage, which is 90 degrees to the direction of crystal growth, or the c-axis. This breakage leaves a flat base (basal pinacoid) with the tell-tale terrace-like markings that look like tiny, wavy rivers running across the flat surface of the crystal. Any forceful knock or pressure can split the stone in two along this direction, and great care is taken when fashioning these stones.
If wearing topaz set in a ring, it would be advisable to either wear it in a rub-over setting to protect as much of the stone as possible. Otherwise, simply wear it in a necklace, earrings or, if you are feeling very fancy, a tiara.
Rhombic cross-section of topaz crystal. Photo courtesy of Lily Faber.
Topaz crystals are typically transparent with multiple straight, parallel striations running down the length of the crystal and a pyramidal termination at the top. They have a rhombus-shaped cross-section which looks like an elongated kite-shape. Inclusions can consist of healed internal fractures (feathers), long tube-like cavities and two-phase inclusions or a cavity with two immiscible liquids. Iridescence can be seen in both rough crystals and cut stones where there are internal fractures, or where cleavage is just starting to extend into the stone from the surface (also known as incipient cleavage). Also seen are variously coloured mineral inclusions.
Topaz cabochon with cleavage and fracture detail. Photo courtesy of Lily Faber.
Whether appreciating topaz in rough crystal or faceted form, it is a lustrous gem of many beautiful colours that warrants attention.
Iridescence within incipient cleavage. Photo courtesy of Lily Faber.
All photos courtesy of Lily Faber unless otherwise stated.
Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.
If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.
Cover image showcasing a large incipient cleavage within a cut stone (seen through table facet). Photo courtesy of Lily Faber.
Featured in the Spring 2018 issue of Gems&Jewellery, Rui Galopim de Carvalho FGA DGA explores how ‘alternative facts’ have resulted in an informal nomenclature that permeates the world of gemmology. Here, he offers some examples of these long-standing quirks in terminology.
From the the Spring 2018 issue of Gems&Jewellery, here Harold Killingback FGA explores chatoyancy in sillimanite cabochons, an optical phenomenon where a band of light, known as a 'cat's eye', appears to hover above the surface of a stone, resulting in a striking lustre and colour.
Every year Gem-A gives its members and students the chance to show off their skills with the camera through the Gemstone Photographer of the Year competition. Have you got what it takes to be Gem-A's best photographer of 2018? Entries are open now and close on August 31, 2018.