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A Brief History of Opal |
Opal is a closely
placed array of millions of spherical particles of amorphous silica,
stacked in a three dimensional grating. Due to the special grating
of the spheres, it is the only known gemstone that has the unique
natural ability to diffract -- that is, to split white light or
ordinary sunlight into all the beautiful colours of the rainbow.
Impurities play no part in creating the colours of the opal as is
the case with many other gemstones. Colour is created when light
is split by voids that have been formed between the spheres. The
size of the voids are critical to the angle at which the light is
split, hence the colour produced varies with the viewing angle.
To see it at its sparkling best, the light should be coming from
over your shoulder.
Australia has some 96% of the world's supply of commercial grade
opal and suffers little of the problems that seem to apply to many
forms of opal from other countries. This is due to the fact that
Australian opal has been laid down under very special sedimentary
conditions. Opal was formed under very special conditions by a complex
ion-exchange process that can now be demonstrated in the laboratory. |
Forms of Opal |
Australian opals are the finest
in the world. Good stable Australian opal has proved to be a sound
investment over the past 25 years. It is one of the few gemstones
that has continued to appreciate in value at a steady rate. But
before you race out and buy one, learn a little about them and in
what form they come and what is available.
They fall into three categories: solids, doublets, and triplets.
SOLIDS: are natural stones which
have been cut and polished without being interfered with. Many have
a natural potch or rock back. |
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| DOUBLETS: are
usually two pieces of opal cemented together. They are made by cementing
a layer of high-grade opal to a black potch back, which enhances the
colour. For economical reasons, many have thin faces. But domed cabochons
made from good quality crystal opal, do in many cases, resemble fine
quality black opal, which is due to the partial absorption of light
by the black back. Their value is only a fraction of that of a solid
black gem of the same quality. Although not always encouraged by the
trade as an investment stone, the better pieces do bring a reasonable
price and are certainly worthy of a place in any good gem collection. |
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| TRIPLETS: are
doublets usually made from a lower grade opal with clear domed caps
cemented to their faces. The hardness of the cap may vary from glass
to quartz, depending on the quality of the opal. The cap not only
protects the opal but magnifies the intensity of the colour and pattern,
greatly enhancing the overall appearance. |
This web-site is currently still in development.
In order to see more opals and to make some great opal bargains in
black opal, white opal, boulder opal, and rough opal please check
out the OpalShop web-site.
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