To understand topaz, a gemstone that has been popular for centuries yet often misunderstood and mistaken for other materials, it is worth revisiting the basics of gemmology.
A stone has to meet three criteria to be considered a gemstone: it must have a beauty which makes it suitable for use in jewellery, it must be durable enough to resist wear and tear, and finally, it must be rare.
Rarity is governed by supply and demand, and this is where it gets interesting for topaz.
In terms of beauty - admittedly a subjective quality - topaz has many features which make it an attractive gemstone.
It is found in a variety of colours, from colourless through to light and dark blue, and including shades of yellow, orange, pink, brown and green.
It forms in relatively large, transparent crystals, and the combination of a high refractive index, a vitreous lustre, and its ability to take a high polish adds to the gemstone’s brilliance and visual appeal.
With a Mohs hardness rating of 8, it also ranks high in durability. Topaz resists abrasions, which dull the surface, making it a suitable gemstone for use in jewellery, including rings.
 |
THE FACTS |
| Hardness: | 8 |
| Toughness: | Brittle |
| Colour: | Colourless, blues, yellows, oranges, pinks, browns, red (rare) |
| Cause of colour: | Unknown except for pink, which is coloured by chromium |
| Main sources: | Brazil, USA, Japan, Africa |
| Acceptable treatment: | Irradiation and heat |
| Unacceptabl treatment: | Radioactivity |
|
The main detraction in this regard is the gemstone’s perfect basal cleavage, which can make cutting and setting of the gemstone more difficult.
As such, facets should not be cut parallel to the basal cleavage, and care should be taken when setting and cleaning to avoid putting stress on the gemstone, which could cause fractures.
With that said, the sheer proliferation of topaz in the market and the ongoing popularity of the gemstone speak for itself regarding its suitability as a material for use in jewellery.
Further adding to the appeal of topaz is its rich history and pedigree.
For centuries, the primary source of topaz has been the renowned Minas Gerais region of Brazil.
The rich, golden yellow, warm orange, and pinkish and reddish orange shades are said to have been favoured by the Russian monarchy in the 18th century, hence being known as the ‘imperial’ colours.
The imperial colours are rare to find in nature, and as such, they are highly sought after and command a high value.
Indeed, the golden yellow colour is likely what most people imagine when they think of the colour topaz, which is particularly amusing when we consider that most topaz found in jewellery stores today is vibrant blue.
With that said, topaz is no stranger to mistaken identity. For most of its history, and before the advent of modern gemmology, it was known as the yellow gemstone, and other yellow gemstones were often sold erroneously as topaz, which had a higher value than citrine.
The pale, blue-coloured material was mistaken for aquamarine, and the colourless topaz was used as a diamond imitator.
In the latter half of the 20th century, it was discovered that irradiating the colourless topaz with gamma rays from cobalt-60, followed by heat treatment, would transform the gemstones into shades of sky blue and steel blue.
The treatments, which are undetectable, should be disclosed; however, they have the benefits of full colour penetration and permanence, making them a good candidate for the mass market.
After all these years of mistaken identity, we now find the market for topaz is divided - there is the imperial topaz, which remains rare and therefore is not as well-known but commands a high value. And then there is the treated blue topaz, which is abundant in supply, very popular and thus quite affordable.
Both are beautiful and durable; they serve as a wonderful example of the difference rarity makes when valuing gemstones.
READ EMAG