Jeweller - June 2021

MULTI-COLOUR & COLOUR CHANGE
Colour Investigation
MULTI-COLOUR & COLOUR CHANGE
Colour Investigation
PROVENANCE SNAPSHOT
TOP 5 MULTI-COLOUR AND COLOUR CHANGE GEMSTONE PRODUCING
ARCTIC
OCEAN
Parti-Colour &
Colour Change
Sapphire
Australia
USA
Kenya
Opal
Australia
Ethiopia
Mexico
Peru
Mali
Alexandrite
Sri Lanka
Brazil
Ammolite
Canada
USA
Ammolite is formed from the
fossilised shells of extinct
ancient molluscs known as
ammonites
Alexandrite was found in Russia’s
Ural Mountains in 1834 and named
after Tzar Alexander II; its red and
green colours matched that of the
Russian military uniform
$AU2.5 million
The world’s largest gemquality
opal, the 17,000-carat
Olympic Australis, was
valued at $AU2.5 million
in 1997 – the equivalent of
$AU4.4 million today
Carla Maxine
Ametrine
Bolivia
54 | June 2021
• Parti-Colour & Colour
Change Sapphire
• Colour Change Garnet
• Parti-Colour Tourmaline
Brazil
PACIFIC• Alexandrite
OCEAN
• Bi-Colour Topaz
• Parti-Colour Tourmaline
• Bi-Colour Beryl
“As an opal
changes its
colours and
its fire to
match the
nature of a
day, so do I”
JOHN STEINBECK
While watermelon
tourmaline is the
best-known, particolour
tourmalines
can occur in virtually
any colour combination
ATLANTIC
OCEAN
Madagascar
Tanzania
• Colour Change Garnet
• Parti-Colour Tourmaline
In the opal you shall
see the burning fire of
the carbuncle or ruby,
the glorious purple
of the amethyst,
the green sea of
the emerald and all
glittering together,
mixed after an
incredible manner
PLINY THE ELDER
• Bi-Colour Zoisite/Tanzanite
• Colour Change Garnet
• Parti-Colour Tourmaline
Sri Lanka
According to legend, the
world’s only source of
ametrine – the Anahi
Mine in Bolivia – is named
after a princess of the
Ayoreo tribe who fell in
love with a Conquistador
122,400 CARATS
WEIGHT OF
THE SAUER
ALEXANDRITE –
THE EQUIVALENT
OF NEARLY 25KG
INDIAN
• Alexandrite OCEAN
• Parti-Colour Tourmaline
• Colour Change Garnet
Mark Antony
– the lover of
Cleopatra – was
said to be obsessed
with opals and
banished a Roman
senator who
refused to sell him
an opal ring
PACIFIC
OCEAN
SPECIAL MENTION
Australia
Opal
Parti-Colour Sapphire
Bi-Colour Zoisite/
Tanzanite
Tanzania
Bi-Colour
Topaz
Brazil
Ukraine
Diaspore
(Zultanite)
Turkey
Australia’s opal fields are
larger than all the opal fields in
the rest of the world combined
Zultanite is a trade name
given to a type of diaspore
found only in the Ilbir
Mountains of Turkey
Colour Change
Garnet
Madagascar
Tanzania
Sri Lanka
USA
Norway
Parti-Colour
Tourmaline
Brazil
USA
Afghanistan
Madagascar
Sri Lanka
Nigeria
Tanzania
Mozambique
Malawi
Kenya
Namibia
Napoleon Bonaparte is
believed to have gifted his
beloved wife Josephine with
a 700-carat black opal
named ‘The Burning of Troy’
THE ANCIENT ROMANS
VALUED OPALS ABOVE
ALL OTHER GEMSTONES
Multi-colour and colour-change gemstones are among the most unique and beautiful of all jewellery crystals.
Here, Jeweller discovers the gemmological phenomena that create eye-catching rainbow hues.
Awe and wonder surround the spectacular phenomenon
of colour change in gemstones. The fascination of seeing
colours shift before one’s eyes can leave consumers
speechless with utter disbelief.
These rarities are chameleons of the gemstone world,
coveted for their ability to change colours in different light.
The human eye perceives light in the visible spectrum,
comprised of red, orange, yellow, green, blue and violet
wavelengths. Colour change gemstones have two
transmission windows in the visible spectrum of roughly
equal size, and the nature of the illumination dictates the
perceived colour.
Alexandrite is a fine example of this magical effect, with
superior quality material producing a dramatic shift that is
sometimes described as ‘emerald by day and ruby by night’;
fittingly, the ‘magician’ in this extraordinary colour play is
none other than chromium, the element responsible for the
rich red of rubies and the vivid green in emeralds.
A member of the chrysoberyl family, alexandrite contains
traces of chromium +3 ions. These ions react to light and
absorb specific parts of the light spectrum giving the
resulting colour.
Natural daylight or fluorescent light contains higher
proportions of blue and green wavelengths and will cause
the gemstone to appear to be green whereas incandescent
lighting, such as an electric globe that contains a higher
proportion of red wavelengths, will cause the gemstone to
appear red.
This mineral’s light-absorbing quality doesn’t end
with colour change; alexandrite also exhibits strong
trichroism, showing different colours when viewed
from different directions.
UNDERSTANDING COLOUR
The Rainbow Connection
55
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Lydia Courteille
QUICK
FACTS
90%+
of the world’s
opal is sourced
from Australia
1
number of
locations where
ametrine,
ammolite, and
Zultanite are
found
$4m
value of
the world’s
largest faceted
alexandrite
The gemstone was first discovered in Russia’s Ural
Mountains in the 1830s, but current sources include Sri
Lanka, East Africa, India and Brazil.
The attractive gemstones produced from Russian deposits
in the 19th century are still considered to be the most
distinctive, displaying vivid hues and bold colour changes.
Modern sources of alexandrite tend to exhibit muddier
tones with a less-precise colour change.
Garnet, sapphire and spinel
Rare colour change sapphires exist, with the varying
colours dependent on the colouring agents. The more
commonly seen and popular gemstones are from Sri
Lanka, and shift from purple under incandescent light to
bluish violet in daylight.
A well-kept secret is Australian colour change sapphires
from the central Queensland gemstone fields that display
some unusual colour changes – brown to green, yellow to
pink, or golden orange to orangey-green.
Rivalling alexandrite and sapphire for hardness and
durability is colour change spinel. This chameleon can
change from blue to purple or from light bluish-violet to
light pink, resembling colour change sapphire without the
hefty price tag.
Colour change garnets are another rare occurrence, with
limited deposits in Sri Lanka, Tanzania and Madagascar.
Fine quality gemstones can produce a strong and attractive
red to green colour change, rivalling that of alexandrite.
Colour change garnet is usually either pyrope type or a
mixture of pyrope and spessartite varieties.
The presence of varying amounts of chromium and/
or vanadium can produce a colour change that flashes
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