Jeweller - May 2020

REVIEW
Gems
L to R: Tourmaline; polished tourmaline earrings, Retrouvaí
Tourmaline: a rainbow in all seasons
The name tourmaline comes from the
Sinhalese word turmali, which means
“mixed”. Colour is the major characteristic
of this gemstone, which is found in more
hues, shades and nuances than any
other gem.
Gemmologists have various names for the
different colours of tourmaline, including
rubellite, verdelite, indicolite, dravite, schorl
and the unique liddicoatite.
Mineralogists, however, would prefer
them to be called by their colour and then
‘elbaite’, which is the mineralogical name
for tourmaline.
Tourmaline is a crystal boron silicate
mineral belonging to the trigonal crystal
system. It occurs as anything from long
and slender to thick, prismatic and
columnar crystals that are usually
triangular in cross-section.
A durable mineral with a hardness of seven
on Mohs’s scale, tourmaline also boasts
strong pleochroism, which means that iit
shows different colours, or depths of colour
when viewed at different angles or rotated.
Tourmaline occurs in all colours, including a
range of bi-colour and tri-colour specimens
– the most coveted of which is the
watermelon tourmaline, named for its pink
centre and green edge. Top specimens are
highly regarded by collectors and usually
cut as slices.
Tourmaline is found in various locations
globally, including Brazil, the USA, Tanzania,
Madagascar, Afghanistan, Pakistan, Sri
Lanka, and Malawi.
Rubellite
Rubellite tourmalines vary in
colour from mid to deep reds
that closely resemble ruby.
The name comes from the Latin rubellus,
which means reddish. Rubellite is one of the
rarest and most valuable tourmalines.
Many gems in the 17th-century Russian
crown jewels that were originally thought to
be rubies are actually rubellite tourmalines.
Verdelite
Verdelite is the term used by
gemmologists to refer to green
tourmalines and there is a broad
range of shades – some are so dark that the
green colour can only be recognised when
the stone is held against the light.
Wonderful examples of verdelite tourmaline
exist in the colour range between bluegreen
and dark bottle-green.
The colour is the result of concentrations of
iron, titanium and, occasionally, chromium
in the crystal.
Indicolite
Indicolite occurs in bright blue
hues to bluish green and good
quality stones are quite rare.
Perhaps the most well-known indicolite
tourmalines come from Paraíba in Brazil.
Paraíba tourmalines have often been
described as neon, as they appear to glow.
Tourmaline
From the Sinhalese
word turmali, meaning
“mixed”, due to its
many colours
Colour: Multiple
Found in: Various
locations globally,
including Brazil,
the USA, Tanzania,
Madagascar,
Afghanistan, Pakistan,
Sri Lanka, and Malawi
Mohs Hardness: 7
Class: Boron silicate
Lustre: Vitreous
Formula: Varies
Dravite
Dravite is found in tones of golden
and tawny brown, and is another
variation of tourmaline for which stones
of good quality are not often available.
There is a yellow tourmaline from Malawi,
discovered in the autumn of 2000, that is
clear and pure with just a hint of green and
circulates under the trade name ‘canary’.
Schorl
Schorl or black tourmaline is
very common, totally opaque, and
inexpensive compared to other
tourmaline. It can also often be found in
much larger sizes –
sometimes more than 70 carats!
Liddicoatite
Liddicoatite typically exhibits extraordinarilybeautiful,
geometrically-patterned colour
zoning. It was recognized as a unique
mineral species in 1977, and was
named in honour of American
gemmologist Richard Liddicoat.
When discovered, it was the sixth tourmaline
species to be recognized – today, there are
14 different tourmaline group members.
Ultimately, tourmaline is an attractive gem
that stands up to its rainbow name. In fact,
the term describes tourmaline so well that
one could have a collection of them in every
colour and feel as though one had gathered
the entire world of gems.
May 2020 | 39