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Decorative
Stones
Low-type zircon of gem quality is found in Sri Lanka,
as worn pebbles in the gem gravels. Low-zircon natural
colors are yellow-green grayish, orange, and brown;
these colors are not improved by heating Often such
stones are mixed into parcels of other gems, such as
sapphires or tourmalines, where their true identity
is disguised.
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Medium-type
zircon is also found in Sri Lanka. Sometimes heating
produces properties like the high type, but more often
heating is unsuccessful at improving the yellow and
brownish natural colors. The presence of radioactive
elements in zircon ultimately causes destruction the
crystalline structure. This process is called metamictization. |
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Zircon
itself is not a rare mineral, and occurs throughout the won
Crystals are common in various types of rocks. In addition
to Sri Lank Cambodia, and Thailand, sources of gem material
include New South Wales, Australia, and the Malaga say Republic.
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DIAMONDS,
GEMSTONES & CRYSTALS
FACTS & FIGURES |
| Some
colorless zircons of natural occurrence exist,
but most blue and colorless stones are the result
of heat treatment. The hardness zircon is 61/2-7
on the Mohs scale. Although there is no distinct
cleavage, zircon is very brittle and should be
handled and worn with ca Optically, zircon is
distinctive, because it is one of the few natural
gems with dispersion that approaches that of diamond.
In addition, the refractive index of zircon is
very high. Colorless zircons cut as round brilliants
therefore have much of the steely brilliance and
dispersive color play diamond.
These
stones can easily be mistaken for diamonds at
first glance. However, diamond is singly refractive,
whereas zircon has w intense double refraction
that back facets of a cut stone may app~ doubled
when viewed through the table. This test alone
may be d nostic, if the doubling is apparent.
Sometimes the zircon is oriented direction for
cutting that eliminates the doubling. In such
cases, gemological tests may be necessary.
Consumer Tips-The brittleness of zircon makes
it especially susceptible to damage when worn
in a ring. Stones in a parcel that are al low
e roll against each other may actually show slight
damage due to chip. of facet edges. For this reason
cut zircons are individually wrapped paper for
shipment.
. 
Colorless
and blue zircons, the most familiar and popular
c varieties, are not very expensive and can usually
be purchased for a. dollars per carat. Very large
stones, however, are rare. |
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Small
zircons may be used as side stones in jewelry, in play diamond
chips. Examination with a strong hand lens or microscope readily
reveal such substitution, since the zircons will show facet
doubling and signs of wear, whereas diamonds would retain
their polish show less chipping.
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