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Colorless quartz or rock crystal
This is much the most common and most widely
distributE variety of quartz. It must have been known since
prehi toric times, and the Greeks named it "crystal,
or ice, b, lieving it to be a form of the latter, irreversibly
frozen t . some process of extreme cold.
Appearance Although quite common,
it has been use as a gemstone (albeit an inexpensive one)
because of itbeauty. It was and still is cut into all shapes,
except, pe, haps, the brilliant, which would mercilessly display
its infF riority to diamond. It has been used much more frequenti
. for the fashioning of elaborate, finely engraved cups, jug;
and vases. Veritable masterpieces were produced in th, past
and there are still places where the tradition is contir ued.
Simpler pieces make use of quartz that has strikin:: inclusions
in the form of long, thin yellow-brown rutile necdies or black
tourmaline prisms, sometimes crossed in var ious ways. Such
quartz specimens make attractive - ornaments, despite being
harder to work.
Distinctive features It is
distinguished from glass, particularly of the type sold under
the name of lead crystal, by its birefringence. Glass also
frequently contains minute ai bubbles. Some difference in
hardness (7 for quartz, nc more than 5 for lead glass) may
also help distinguish it.
Occurrence Large quantities
of quartz come from Brazi and Madagascar, but the colorless
variety is found almost everywhere. In the nineteenth century,
magnificent objects were made from quartz discovered in the
French and Austrian Alps.
Value As a gem, its value is extremely low.
It is now cut almost exclusively for collectors and amateurs.
As an ornamental material, its value largely depends on the
way in which it is fashioned. Fine examples may be quite valuable
and more costly than similar pieces made from more opaque
materials. Finely worked antique pieces are, of course, still
more valuable.
Simulants and synthetics The
confusion of lead crystal glass with rock crystal is generally
due to misunderstanding rather than imitation. Large amounts
of synthetic quartz are produced nowadays, but only the amethyst
and citrine varieties are of interest to the gem trade. The
colorless variety is made only for technological purposes.
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