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Left: Emerald | Right: Goshenite
Left: Emerald | Right: Goshenite

Colour investigation: Beryl (Part 1)

What do emerald, aquamarine, heliodor and morganite have in common? They are all from the group of gemstones called beryl and are coloured by trace impurities. KATHRYN WYATT reports.

Beryl also comes in a colourless variety called goshenite, and red beryl is so rare that you will not likely see in jewellery. All have a hardness of 7.5 to 8 on the Mohs scale.

The vibrant colour of emerald has been adored from Roman times. Cleopatra had her own mines and the Incas worshipped emeralds and used them in jewellery long before the Conquistadors conquered Colombia in the 1500s and opened mines to trade on the subcontinent and Europe.

Moguls prized the gem and secured vast collections before they were whisked off to Iran by Persian invaders in the 16th century.

Created by trace impurities of chromium and vanadium, the intense green colour is the most prized. The price drops when accompanied by a bluish tinge, and continues to devalue further when coloured a yellowish tinge from iron impurities. When the colour of beryl is too light to be called emerald, it is termed ‘green beryl’ and the price plummets again.

Colombia remains the major source of emeralds, retaining the best reputation and usually commanding a price premium. Clients often ask for a Colombian emerald thinking it will be of superior quality. However, not all Colombian emeralds are equally fabulous.

"The best cut to show off the brilliance and colour of most beryl is, of course, the emerald or step cut"

Emeralds are currently sourced from many parts of the world, including Russia (sourced from the Urals for more than 100 years), Zambia, Brazil, Zimbabwe, Afghanistan and Ethiopia. Some emeralds from these mines will rival the best Colombian emeralds. One should never buy a gem just from its location provenance.

You need to see the stone’s colour and brilliance. The best cut to show off the brilliance and colour of most beryl is, of course, the emerald or step cut. The ‘cut off’ corners also protect the stone from chipping.

Emeralds typically have many inclusions; the French say they have a Jardin (garden) inside them, affecting the clarity. The inclusions also make emeralds a more brittle gemstone, often confused with it being soft. It should be known that all emeralds have the same hardness, but the inclusions make them prone to breaking.

To help improve their clarity and colour, emeralds are treated in several ways. They are usually “oiled” at the mines– a process that uses oil to fill the cracks and inclusion spaces in a technique practised for centuries. This treatment is standard and must be disclosed, as these emeralds should not be cleaned in an ultrasonic cleaner or with soapy water. Doing so removes the oil and renders the emerald less desirable.

Emeralds can also be filled with a glass or a resin-like substance to also improve durability, however the stability of these treatments varies so this treatment must also be disclosed, ultimately affecting the price of the gemstone.

Because emerald is one of the more prized gems, it has been made synthetically by various methods. Synthetic emeralds are easy to detect as the colour is vibrant and the gemstones are free of inclusions. A large natural emerald free of inclusions is very rare.

It is clear that the range of colours in emeralds are diverse and should be appreciated by jewellers and their clients alike.











ABOUT THE AUTHOR
Kathryn Wyatt

Contributor • 


Kathryn Wyatt BSc FGAA Dip DT, is a qualified gemmologist, diamond technologist, registered jewellery valuer, educator and member of the Australian Antique & Art Dealers Association. For more information on antique and vintage jewellery courses, visit: gem.org.au









Sunday, 16 December, 2018 08:29am
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