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women carried small spheres of colorless quartz to cool
their hands in the heat of the day. In modern times
quartz has acquired many uses, most notably the control
of radio frequencies. The millions of "crystal
sets" made during World War II contained a thin
slice of quartz in their tuning circuits.
Quartz's
valuable electrical properties make it useful in such
devices as phonographs. More recently quartz has been
used in the manufacture of accurate watches. Its optical
properties make it valuable for use in special lens
systems and prisms. Colorless quartz, to the jeweler,
is rock crystal, a material with many gem uses.
It
can be faceted for wear, as well as carved into a variety
of decorative objects Sometimes quartz forms in an environment
where it incorporates millions of tiny bubbles and fluid
inclusions, giving the material a white or "milky"
appearance. Gold veins are often filled with milky quartz.
This form of quartz has little gemological use.
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Smoky
quartz, however, is a popular gem material. The cause
of the color is not fully understood, but is believed
due to the action of radioactivity. Very dark smoky
quartz is known as motion. Gems from Scotland were known
as cairngorm (after the Cairngorm Mountains), although
the supply from this source is now essentially exhausted.
Today fine smoky quartz comes from the Swiss Alps, Brazil,
Japan, Colorado, Maine, North Carolina, and California. |
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Citrine
is yellow quartz, and the color may grade into a smoky brown.
The color is due to the presence of iron, though some lemon-yellow
quartz on the market derives its color from irradiation, and
is not naturally colored. The primary source of citrine is
Brazil. The color range of citrine is very similar to that
of precious topaz. This has led to widespread misuse of the
terms "citrine topaz" and "quartz topaz,"
both of which are quartz.
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Quartz Gems |
| Quartz
Gems
Quartz is one of the most common minerals on earth.
It occurs in measurable quantities in almost every
type of rock exposed at the earth's surface. Most
beach sands are composed of quartz grains that
have been rounded by wave action and mixed with
other mineral fragments.Chemically quartz is a
simple oxide of silicon, the two most com¬rnon
elements in the earth's crust.
This material
forms quite easily in a variety of geological
environments. Quartz may crystalIize from molten
rocks in their final stages of solidification.
It frequently deposits in mineralized veins, usually
from dilute solution in superheated watery fluids.
Quartz makes up a large part of most pegmatites,
and is often found filling cavities and cracks
in a wide variety of rock types.
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Quartz
is a ubiquitous geological "cement"
and welds together such rocks as sandstone.If
allowed to form in an open space, quartz forms
magnificent crystals with well-developed external
forms of great beauty. The huge range of possible
geological conditions in which quartz can crystallize
allows for the existence of many external crystal
shapes, making quartz popular among mineral collectors.
To the gem lover, however, the interesting thing
about quartz is the range of lovely colors it
acquires,and the panorama of interesting inclusions
it displays.
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Pure
quartz is colorless. It was used as ornamental material as
early as the Stone Age, and by the time of ancient Rome it
was known that a wedge of quartz could be used as a lens to
concentrate the sun's rays.
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