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Synthetic
Quartz
Natural quartz is common and inexpensive. Yet synthetic
quartz can be made in sufficient quantity and at low
enough cost to make gem quartz manufacture worthwhile.
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Citrine,
or yellow quartz, is colored by iron. Amethyst is made
by adding specific impurities that do not produce a
visible color, but which cause a purple coloration when
the quartz is irradiated by a radioactive source. Colorless
quartz is made in ton quantities for use in electronic
applications, but is seldom cut as a gem. Green quartz
is also manufac¬tured in limited quantity. |
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Quartz
is synthesized by the so-called hydrothermal process. This
is the way most natural mineral crystals form, in veins and
cavities within the earth. The process is basically the deposition
of material from hot-water solutions in which the mineral
material is dissolved. Natural solutions are very dilute and
mineral crystals may take many year¬ form. In the laboratory
the action is speeded up by dissolving the desired material,
in this case chunks of natural quartz, in hot water containing
chemical solvents.
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Synthetic Beryl |
| Synthetic
Beryl
Of the various
beryl colors, by far the most valuable is the
deep green at emerald. Experiments at emerald
synthesis are known as early as 1848 but crystals
weighing more than one carat could not be synthesized
until 1912. Richard Nacken, who also developed
the basic process for quartz synthesis, produced
small emerald crystals up to about 1A inch long
using a hydrothermal process similar to that used
for quartz. Later German experimenters succeeded
in growing small emeralds of fine color which
were marketed as "Igmerald" by the I.
G. Fabens industries conglomerate as early as
1934.
After World War II Carroll Chatham of San Francisco
introduced emeralds of large size and fine color.
These were the result of research dating back
to 1930, and apparently a flux-growth technique.
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More
recently synthetic emeralds have been manufactured
by the Linde Air Products Company, Pierre Gilson
of Paris, Zerfass of Ger¬many, and others.
The Linde emerald is grown hydro thermally using
142 seed plates of colorless beryl. Gems are cut
from the emerald that accumulates above or below
the seed plate, so large thicknesses are required
and are expensive to prepare. Large crystals of
superb color are made by Gilson, and clusters
of synthetic crystals are frequently offered for
sale as jewelry items. |
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Synthetic
emeralds can usually be distinguished from natural gems
by the presence of characteristic inclusions. Natural emeralds
have specific kinds of inclusions which are often diagnostic
of the country or mine of origin. Sometimes present are
so-called "three-phase" inclu¬sions consisting
of a cavity filled with liquid, within which is a gas bubble
and a crystal of sodium chloride or another salt.
Synthetic
emeralds do not generally display such inclusions, but may
contain pieces of flux, or other characteristic internal
markings. Detection al¬ways requires the use of a microscope
and sometimes additional gemological testing instruments
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