Jeweller - November 2018

GEMS
COLOUR INVESTIGATION: BERYL (PART 1)
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.
EMERALD
GOSHENITE
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.
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.
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.
THE BEST CUT
TO SHOW OFF
THE BRILLIANCE
AND COLOUR OF
MOST BERYL IS,
OF COURSE, THE
EMERALD OR
STEP CUT
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. i
KATHRYN WYATT is a qualified gemmologist,
diamond technologist, registered jewellery valuer,
educator and member of the Gemmological
Association of Australia. For information on
gemstones, visit: gem.org.au
November 2018 Jeweller 37