I have written this as a brief overview of some of the more
common gemstones, intended to educate a novice gemstone lover.
I find gems one of the most exciting parts of jewellery. The
colour and sparkle has intrigued everyone from royalty to pauper since the
beginning of civilisation. These objects have been prized not only for their
beauty, but for their physical, symbolic and mythical properties.
Colour is the
first thing that strikes the casual observer, but once you spend a little more
time with the various stones in front of you, you start to realise that there
are many other aspects that distinguish one stone type from another. The way
the stone shines, reflects light or how some stones seem oilier and others
crisper. Some stones have distinctive ways of playing with the light. Noticeable
examples would be the cat’s-eye effect that stones like moonstone, star-sapphire,
star-rubies and tigers-eye exhibit.
There aren’t many exhibitions in nature that can rival
gemstones complete spectrum display of colours.
To illustrate the hues of some of the most commonly seen
gemstones, I have made a colour-wheel. Although using opaque ‘computer’ colours
is a poor substitute for the vibrant real article.
Each type of stone has a large variation in hue, the colours
I have chosen to represent each stone are the most commonly found colours.
Other stones that don’t fit
into the above chart would include- Tigers Eye, Labradorite, Moonstone, Opal,
Pearl and Rainbow Tourmaline. In the black range you find onyx, black agate,
black tourmaline and black diamonds to name only a few. 
Tiger's Eye
Labradorite
Rainbow Moonstone
Moonstone
White Opal
Black Opal
Rainbow Tourmaline
Onyx
Black Tourmaline
A few handy technical terms used to differentiate
physical properties of one stone as compared to another.
When a ray of light meets the surface of a stone, some of
the light is reflected back to the observer and some passes into the
stone. Due to the different densities light will slow down and bend (refract)
at a specific angle determined by the specific physical properties of that type
of stone which is ultimately determined by the chemicals that typically make up
that kind of stone. For example a peridot is a peridot because of it’s specific
chemical composition.
Lustre is the quantity and quality of light that is
reflected back to the observer. Reflecting is the mirror-like bending of light
on the surface of a stone. A stone like diamond has a high lustre, whereas
stones like jade or peridot can have a greasy lustre.
Brilliance is the percentage of light that refracts
back to the observer. Refraction is the bending of light within a stone. Each
type of stone has a specific angle of refraction due to it’s specific physical
properties.
Scintillation is the flashing of light off of the
facets.
Facets are the flat planes used to polish or cut a
natural stone. When you think of a diamond you are thinking of a facetted
stone, which is comprised of lots of flat areas. A cabochon cut stone on
the other hand is a simpler cut that has a flat bottom and the rest of the
stone is shaped into a dome.
Cabochon Cut Moonstone
Facetted
Diamond
Generally speaking, the more intense the colour of a
gemstone the more valuable it is. Although there is often a lot of personal
preference when choosing a coloured stone, sometimes people love the more
washed out hues.
GEMSTONE
DESCRIPTIONS
CITRINE ranges in colour
from a very pale yellow to a warm orange colour. Citrine is one of many stones
that falls under the umbrella name of Quartz. Others include amethyst, smoky
quartz, rose quartz, rock crystal and even stones like tiger’s eye, onyx and
agate. All of these stones have the same chemical composition and are only
distinctive because of trace chemicals that change the colouring of the stone.
Because all quartz stones are formed from the same dominant chemicals,
they all have the same physical properties like hardness and lustre. They also
all form or grow in nature in hexagonal crystals. The above doesn’t apply to
rose quartz because they are formed in a non-crystalline, ‘massive’ form
and tigers eye.
Quartz
watches use a chip of man-made quartz that vibrates at a precise
frequency when a watch’s battery pushes a charge through it. This accurate
frequency is then harnessed and converted to seconds to make sure the
time-piece is accurate. That is why most modern watches have the words Quartz
written on the dial. It means they are battery powered.
Quartz
is the second most abundant mineral in the Earth’s crust.
Citrine is
the birthstone for November.
Three images
of citrines to illustrate the different hues
YELLOW DIAMONDs range from
a pale canary colour to an intense yellow. Intense fancy yellow diamonds are as
valuable as top white coloured diamonds.
South Africa
is regarded as the home of diamonds as it was home to the first major discovery
of large amounts of diamonds in one kimberlite (rock type) pipe found in the
town Kimberley, South Africa.
Diamond is
renowned for being the hardest natural substance on earth, a result of its
extremely strong chemical bond. The word diamond is derived from the ancient
Greek adámas, which means unbreakable. Diamonds are not unbreakable but
are very resilient. I have heard of people testing a diamond by hitting it with
a hammer. This will crush the diamond. Not clever! Another inaccurate test if a
stone is a diamond or not is to scratch a glass window with the stone in
question. Many stones are harder than mineral glass and as a result a host of
stones will be able to scratch glass, including many diamond simulants (stones
that can be confused with diamonds). The most common test for diamonds is a
hand held machine that omits heat into the stone and measures the amount of
heat that is conducted away, Diamonds have excellent thermal conductivity. This
test is also not full-proof as certain man made stones are made to deceive
certain aspects of diamonds and can fool this diamond testing instrument.
The term fancy diamond indicates that the amount of yellow
in the diamond is sufficient to no longer penalise its price for being yellow,
but instead creates interest because of its rarity and interesting colour.
Other fancy diamond colours are pink, blue, green and the extremely rare red.
YELLOW SAPPHIRE. Sapphire
is a term for all stones that are corundum except for ruby and an
extremely rare corundum called padparadscha. Similar to quartz being an
umbrella name for a few varieties of stones, corundum is a species of
stone. All three variations of this species have an identical chemical
composition and identical physical properties. If the corundum has
enough chromium trace elements then the corundum is known as ruby and is
red to pink in colour. A pinkish-orange variety of corundum is called
padparadscha. Other than padparadscha and ruby all corundum is called
sapphire. The most commonly known colour for sapphire is blue, but there are
many other colours available, including yellow, pink, green and purple. Many of
these sapphires have recently been discovered in East Africa.
Yellow
sapphire has a pure, intense colour and has a good sparkle.
Sapphire (corundum) is second hardest of all
gemstones, 9 on the Mohs hardness scale. This hardness leads to its use as a
harder, tougher glass. Today most top-end watches are fitted with sapphire
crystal glass and as a result are highly resistant to scratching.
Some of the
colours sapphires exhibit.
IMPERIAL TOPAZ is the
pinkish, orange form of topaz. Topaz is the 3rd hardest gem, after
diamond and corundum (ruby & sapphire) and has a Mohs hardness reading of
8. Topaz is found in almost all colours, with imperial topaz being the most
prized form of topaz.
The word
‘topaz’ is thought to come from the Sanskrit word ‘tapas’, meaning fire. Topaz
was revered by Egyptians as a link to Ra, the sun god and the Roman’s linked it
to their sun deity, Jupiter.
AMBER is an organic gem
and is as such not really a stone. It is fossilized tree resin that has been
exposed to pressure and high temperatures outside the earth’s crust, whereas
gemstones are formed through pressure and temperature under the earth’s crust.
Because amber is organic in nature it is softer and can burn at much lower
temperatures. These constraints have to be taken into account when designing,
making or repairing a piece of amber jewellery.
Amber is
typically yellow, orange or brown, but can be red, green, blue and black.
The most
famous deposits of amber are from the Baltic region.
Amber is
typically around 100 million years old, but examples older than 300 million
years have been found. As such they are an important link to previous
eco-systems. Humankind has worn amber since the stone-ages.
HESSONITE and SPESSARTINE are orange to
red garnets. Hessonite is sometimes called cinnamon stone and is a
little softer than most other garnets.
Top quality,
orange-yellow spessartine is called mandarin garnet.
The Garnet
group of stones is one of the more complicated stones to explain because
like corundum (sapphire & ruby) and quartz (amethyst, citrine etc) there are
quite a few different variations of the garnet group, but in garnet’s
situation each stone has a slightly different chemical make-up and as a result
slightly different physical characteristics (e.g. hardness or natural crystal structure).
FIRE OPAL
has a warm orange colour and is transparent to translucent in appearance.
Fire opal can be faceted, whereas conventional opal is cut en cabochon. Fire
opals do not exhibit the play of colour that most people associate with opals.
Mexico is the most common source for these unusual stones.
SMOKY
QUARTZ is part of the quartz group of stones and is one of
the cheaper stones available, often found as large crystals. It is most
commonly found in a chocolate brown colour but can have undertones of clay or
tend towards black (called Morion). Smoky quartz from Scotland is called
Cairngorm and normally has a smoky, yellow-brown colour.
BROWN
TOURMALINE is one of many colour variations of tourmaline. Being
based in South Africa we normally get our tourmaline from Namibia (especially
the brown and green colours) and newer colours like blue and red from the east
of Africa (Mozambique and Madagascar). Brazil is famous as a supplier of
tourmaline as well as many other valuable gemstones.
ALMANDINE
and PYROPE garnets
are typically wine red in colour and range from a blood-red colour (Pyrope) to
a dark red to the point of being almost black (Almandine). This is the colour
people normally think of as a garnet. The red colour is the source for
the Greek influence on its name “fire eye”. Pyrope and diamonds are often found
in the same kimberlite pipes.
RHODOLITE
is the pink to red colouring of garnets with a similar make-up to
Almandine & Pyrope. In Greek rhodolite loosely means "rose-like".
Tourmaline (RUBELITE) is the pink to red colouring of
tourmaline. As with most tourmalines they were traditionally found in Brazil,
but have recently been found in Zambia, Mozambique and Madagascar.
A range of
different tourmalines.
RUBY ranges in colour from
a so-called pigeon-blood red to a pinkish red.
Ruby is one
of those stones that doesn’t form as large stones and as a result the price
increases dramatically as rubies get larger.
As mentioned
earlier ruby is the red variation of the species corundum. This red
colour is due to the trace element chromium in its composition. This red colour
is the root for its name ‘ruber’, or red in Latin.
Ruby is the
second hardest commonly found natural stone.
Rubies are
normally cut into facetted gemstones when transparent, but some opaque stones
show a 3 or 6 point star effect, called asterism. This ‘star’ moves as a light
source is refracted off of the many needle inclusions within the ruby.
Traditionally
hand-wound watches were referred to as 17 jewels and automatic watches as 21
jewels, this was because natural rubies used to be used as an axis for moving
parts in the mechanism. These ‘jewels’ have been replaced by synthetically
manufactured rubies for many decades. The first laboratory manufactured rubies
were made in 1837 and the first commercially viable corundum was made in
1903.
Red and pink examples
of Ruby.
PINK
TOUMALINE is another colour variation of tourmaline. As with most
tourmalines it has a subtle brown undertone to the dominant colour. It is
almost a more natural version of a pink stone, whereas pink sapphire has
a very intense, vivid, pure pink colouring.
PINK SAPPHIRE Although
blue is the most common colour associated with sapphires, pink is another
example of the corundum species. Similar to other colours of sapphire,
the pink colour is pure and vivid. Similar to ruby the colour comes from trace
elements of chromium. There is an academic point of transition between pink
sapphire and ruby, which is vital to its price. If the stone is deemed to have
enough chromium in it’s make-up to be called a ruby, then its price increases.
Found in
East Africa, Burma, Sri Lanka and India.
PINK DIAMONDs are also a pure
pink in colour. Natural diamonds are often paler, while treated pink diamonds
are normally more intense in colour.
Pink
diamonds have recently increased in demand with celebrities wearing them.
Nearly all
pink diamonds come from the Argyle mine, which is found in the Kimberley region
in the far North Eastern corner of Western Australia. The Argyle mine is
interesting in that it is a mine based on a different type of volcanic pipe
than the conventional kimberlite pipe, called a lamproite pipe.
ROSE QUARTZ is a massive
form of quartz and is normally translucent, rather than transparent. It
is also often cut into en cabochon or into simple facet cuts.
It has an
elegant pale pink colour.
The word
‘massive’ implying that the mineral grows without a regular crystal structure
as per most gem-quality stones. This massive aggregation means the stone will
always have a milky appearance.
KUNZITE
is another pale pink stone and has a very subtle blue undertone. Kunzite
can fade in colour if overexposed to light. It is found in Brazil, Canada and
USA and has a hardness of 7.
MORGANITE is very similar
to Kunzite in appearance. Morganite is the first stone discussed in this
article from the Beryl Species. Other variations in the Beryl
family are emeralds, aquamarine and a yellow stone called heliodor. Morganite
was named after the banker J. Pierpoint Morgan.
The beryl
species has a hardness of 7½ and is as such on the softer side for a valuable
stone.
I find that
morganite has a subtle brown undertone, whereas kunzite has a hint of blue in
the pink.
AMETHYST is another member
of the quartz species. Amethyst ranges from the subtle pink ‘rose de
France’ colour, similar to morganite, to a distinctive deep purple colour. The
colour has been associated with the Roman Catholic Church traditionally being
worn by bishops and other clergy as a symbol of piety & celibacy. The deep
purple colour has also often been worn by royalty.
The root for
the word amethyst comes from the ancient Greek belief that the stone protected
against drunkenness. The fact that many of the traditional feasts occur in
February may be the reason why this talisman against drunkenness would be the
birthstone for February.
Amethyst is
often patchy in colour, with an interesting anomaly called Ametrine which is a
stone that is cut from a crystal that exhibits both the yellow, citrine colour
and the purple, amethyst colour.
Amethyst is
found worldwide.
TANZANITE is a relatively
new stone to the gemmological world having only been discovered in the foothills
of Mt Kilimanjaro in 1967.
Tanzanite
has a beautiful sparkle that shows off its distinctive dichroism, the stone appears
to be dominantly blue when viewed along one axis and violet when viewed on
another axis.
With a Mohs
hardness of 6.5, tanzanite is relatively soft for a valuable stone and as such
should not be set into an everyday ring, unless the wearer is aware that it
will lose its distinctive sparkle as soon as the crisp facets are sanded down
with wear. As a pendant or earrings the stone should be exposed to very little
wear and will retain its beauty.
In 2002
Tanzanite was entered into the list of birthstones as the birthstone for
December.
Tanzanites
have been the subject of extensive marketing campaigns that usually hinge on its
roots as an African stone found only in one location, and as such will become a
collector’s item in time.
Tanzanite’s
name was changed by Tiffany & Co from Blue Zoisite to a name that refers to
its country of origin.
IOLITE
is the gem variety of the mineral cordierite and is a good example of a stone
that has similar colours to another, in this case tanzanite or sapphire, but is
still distinguishable in its lack of colour intensity and fire. Sometimes
called water sapphire, it is found in colours that range from pale to extremely
dark smoky-blue to bluish-violet. Like tanzanite, iolite also exhibits
pleochroism. Iolite is normally found in Sri Lanka, Madagascar, India and Burma
and occasionally in Namibia and Tanzania.
BLUE SAPPHIRE is typically
royal blue in colour, but can also have distinctive violet overtones that can lead
to confusion between sapphires with tanzanites. As mentioned above, sapphire is
the broad description of any corundum stone that is not a ruby or a
padparadscha, although most people think of sapphire as being blue.
Sapphire is
the second hardest natural mineral and is often synthetically manufactured for
this industrial purpose, most commonly as scratch-resistant glasses for better
quality watches.
Opaque to
translucent stones can exhibit the star-like asterism.
Sapphire is
the birthstone for September.
The best
blue sapphires normally hail from India, Sri Lanka, Burma, Brazil and Thailand,
with newer deposits being found along the east coast of Africa.
LAPIS
LAZULI is a combination of several stones, typically lazurite,
sodalite, pyrite (‘fool’s gold’) and calcite. Too much of the white calcite
lowers the price of the lapis. Lapis has been mined from the same area in
Afghanistan for 6000 years. It is mined elsewhere, but Afghanistan still bears
the best quality. Lapis lazuli means blue rock and has a distinctive opaque,
rich, blue colouring with brassy pyrite inclusions. Along with sapphire, Lapis
is a birthstone for September.
TURQUOISE
is another opaque stone that smacks with ancient appeal. Both Lapis and
Turquoise stones were used in the ancient Egyptian dynasties. Some of the more notable
sources of turquoise are Iran, Sinai and USA. The name turquoise comes from the
fact that turquoise reached Europe through Turkish trade routes. The colouring
is sky blue to greenish. Typically turquoise still has portions of the rock
matrix in it, which give turquoise its earthy look. Recently reconstituted
(crushed turquoise powder that has been reformed) and stained howlite have
confused the public about the validity of natural turquoise.
BLUE TOPAZ is the most
common form of topaz, with other colours being pink, yellow, gold and
occasionally green. Most blue topaz is treated colourless topaz. Typically blue
topaz comes in 3 hues of blue: a pale, sky-like blue which is a close stimulant
(imitator) of aquamarine; a bright pale-blue colour, often referred to as
Swiss-blue topaz; and a darker blue that seems to have a shade of grey in it
often referred to as London-blue topaz.
Topaz is the
3rd hardest natural stone after diamond and corundum and has
a Mohs hardness rating of 8.
AQUAMARINE is typically a
pale blue variety of the mineral type called beryl, which also includes
emerald.
Some
aquamarine can have an undertone of pale green, which gives the stone its ocean
like name.
Aquamarine
is found in Brazil, Pakistan, Afghanistan, the Urals, Nigeria and a darker
variety from Madagascar.
EMERALD is the green variation of the
Beryl family.
Emerald has
always commanded a high price, especially very rare inclusion-free pieces.
Emeralds are
synonymous with inclusions, to the extent where a stone’s inclusions can be
used to identify from which mine the emerald originates.
Beryl
has a Mohs hardness rating of 7.5, which is relatively hard, but because
emerald is expensive and due to its tendency to crack, it is thought of as a
delicate stone that needs to be treated with care. The brittleness of emerald
has resulted in a special cut called the emerald cut, which is now used on most
stones. The idea behind the emerald cut is to remove the corners of a rectangle
as this is the most common place for a brittle stone to chip.
Emeralds
were mined in Egypt up to 3500 years ago. Emeralds were also sacred to the
ancient Aztec and Incan empires. Today some of the finest emeralds come from
Colombia other sources are as varied as Zimbabwe, Zambia, Madagscar,
Mozambique, South Africa, Namibia, Tanzania, India, Australia, Brazil, Russia
& Austria and many more.
An emerald-cut emerald.
GREEN
TOURMALINE is relatively common in South Africa because of the
amount of tourmaline available in Namibia. The green stones from Namibia
typically have a yellow or brown undertone. Recently Mozambique discovered a
tourmaline that rivals the Brazilian Paraiba, which has a very intense
blue-green colour and is by far the most valuable tourmaline. Emerald-green
stones are typically found in Tanzania and Brazil. Tourmaline has a Mohs
hardness of 7.5.
TSAVORITE was first discovered in 1967
near the Tanzanian and Kenyan border. It is now mined near the Tsavo
National Park in Kenya.
One other source of tsavorite has been discovered in Madagascar.
Tsavorite is
a grossular form of garnet. There are other forms of grossular garnet
but none are gem-quality, an example being the confusingly named Transvaal
jade, which is not jade at all, but is rather a massive aggregation of green,
grossular garnet. The word ‘massive’ implying that the mineral is grown
without a regular crystal structure as per most gem-quality stones. This
massive aggregation means the stone will always have a milky appearance.
The stone
has a pure, leafy green colour to it.
JADE refers to two
different minerals, NEPHRITE jade and JADEITE jade. They are
completely separate minerals with different chemical combinations, but they
look similar and have both been used as jade for many centuries.
The most
expensive variety is emerald-coloured, translucent jadeite. Nephrite
is typically paler in colour.
Jade was
used as weapons or blades before the metal age. Jade has been closely linked to
ancient societies such as the Chinese, Mayans and Maoris, with many examples of
delicately carved statues and jewellery still in existence.
Sources of jadeite
are Burma, Guatemala, Japan & USA.
Sources for nephrite
include New Zealand, Burma, Siberia, Russia, China, Australia, USA, Canada,
Brazil, Mexico, Zimbabwe, Poland, Germany & Switzerland.
Jadeite
is harder and tougher than nephrite. Jadeite ranks at 7, while nephrite
ranks closer to 6 on Mohs hardness scale.
GREEN AMETHYST is a
confusing name that refers to green quartz. Both amethysts (violet) and
green amethyst come from the quartz species and have identical
properties.
The colour
is a pale, peppermint green and is very popular.
PERIDOT is the gem-quality
of the mineral olivine and is one of the few stones that only occur in one
colour, an olivey, green colour with brown undertones.
Most peridot
is from Arizona, but is widely found with some of the best rough coming from
Pakistan. Peridot has even been found on meteorites.
Peridot has
a hardness of 6.5, but is brittle.
Peridot is
another stone that has been mined from ancient times. Egyptians mined peridot
from an island in the Red Sea over 3500 years ago.
Peridot is
today the birthstone for the month of August.
DIAMOND is the hardest
mineral on earth with a hardness of 10 on the Mohs scale, which is four times
harder than the next hardest mineral, corundum. The combination of its hardness
with its sparkle has made it the most prized gemstone. Diamonds are famously a
form of an extremely strong bond of pure carbon. Diamonds are formed under
ultra high temperatures and pressure, which is recently being reconstructed to
manufacture man-made (synthetic) diamonds. In nature diamonds are formed
between 100 and 280 km below the earth’s surface at temperatures between 900
and 1300 °C and the growth occurs over periods from 1 billion to
3.3 billion years (25% to 75% of the age of the Earth).
Diamonds are typically brought to the earth’s surface by volcanic eruption,
although some diamonds have come to the earth’s surface by means of asteroids.
The name
‘diamond’ is derived from the ancient Greek ‘adámas’ for unbreakable.
Diamonds are thought to have been first recognized and mined in India up to
6000 years ago. In western countries the wearing of diamonds was generally the
prerogative of royalty. The French Revolution and resultant selling of royal
jewellery and a century later the finding of constant supplies of diamonds in
South Africa led to diamonds being used regularly in every-day jewellery.
Diamonds,
along with other minerals and sought after resources, have been used to fuel
civil wars and human rights violations, mostly in Africa. The atrocities linked
to ‘blood diamonds’ were popularised in the late 90s with the Kimberley Process being initiated in May 2000
by South Africa. By 2004
the World Diamond Council reported that the percentage of illegal
diamond trade as a proportion of the world's diamond production had fallen to
approximately 1%.
Historically
South Africa was the biggest source of quality diamonds, but they have now been
overtaken by Botswana, with Russia, Canada, India, Brazil and Australia having
significant reserves. Although just below half of all diamonds are found in
central and southern Africa.
Diamond is
unusual in that the colourless variation is the most sought after colour,
although recently yellow and brown colours are becoming popular. Naturally
coloured red, pink, blue and green diamonds are rare and as a result extremely
expensive.
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