History & Introduction
Zircon is not a very well-known gemstone, still it is one of the most important
gemstones at present. Zircon confuse people with the artificial diamond simulant
and cubic zirconia. However in practical the two are completely different - cubic
zirconia (CZ), is a lab-created synthetic material, whereas zircon is a naturally
available gemstone having a different chemical composition. Still before the introduction
of diamond simulants such as cubic zirconia and moissanite, due to the property
of high dispersion and refractive index white zircon was actually one of the most
popular diamond substitutes, and was often marketed under the misleading trade name
of 'Matura diamond'. Zircon gemstone is even remarkably dense and shows a very pronounced
level of birefringence. Zircon has such high birefringence-facet mirror or screen
may appear blurred.
Zircon is produced in a wide variety of colors from which the white or colorless
probably is less valuable or important. The most famous stone this time is blue
zircon, usually is available with green pleochroism that result in interesting colors
like blue-green. When brown zircon is heated, then it result in the production off
blue Zircon. However, only few of the brown materials are keyed to turn blue while
heated normally available in Southeast Asia that is why most blue zircon comes from
Cambodia or Burma physical structure. Blue zircon is one of the traditional modern
birthstones for December.
Zircon mineral is extremely important, in fact its importance led to the emergence
of the discipline of 'zirconology' in gemology. Zircon gemstone is considered as
the oldest mineral on Earth having samples available in Australia which are around
4.4 billion years old. As per the scientists the zircon actually contains trace
elements of uranium and thorium, both the elements are known with known half-lives.
Due to the uranium and thorium such tremendous variations are caused in the physical
properties of zircon. Zircon gemstone is naturally classified as low, medium and
high zircon, related with the presence of optical properties. Low zircon is naturally
brownish to green in color. Zircon in green is hardly seen in the gem trade and
is highly sought after.
Recognize - In composition the gemstone is zirconium silicate.
As per its gemological characteristics it displays a great varieties such as hardness
ratings spanning from 6.5 to 7.5 on the Mohs scale. Zircon is easily distinguished
by its prominent birefringence; when looking down through the table of a stone,
the doubling effect of facet edges is easily noticeable. It even carries a high
refractive index that ranges from 1.810 to 2.024, with a density ranging between
3.93 and 4.73. Zircon even has a relatively high dispersion rating, showing fire
and brilliance comparing with fine diamond.
Availability - Zircon is the oldest mineral found on earth; even
older than the moon, the formation is around 4 billion years ago. In fact it is
the first crystal to form in molten granite as it cooled to form rock. Sri Lanka
is the best deposits of green metamict 'low' zircon. It is also found in Burma (Myanmar),
and even in Cambodia. Mainly the deposits of zircon come from Burma, though Australia
has the oldest deposits over 4.4 billion years. Other prominent sources are Mozambique,
Brazil, Tanzania, Korea, Madagascar, Nigeria, Thailand and Vietnam.
Usages - Zircon available in every colors are used as gems, however
golden-brown, blue as well as white are frequently used colors. Blue Zircon available
in lively pastel blue is a well-known color and has a rarely striking bright blue
color. Colorless Zircon is available in cut that is brilliant to bring out its fire
to its fullest. More often it is used as natural alternative to diamond, which is
available at lower price. The other color forms (green, yellow, pink and purple)
are less used in jewelry.
Buying Guide
Color - Zircon in its purest form is completely colorless (white),
however because of the presence of impurities, it occurs in a large variety of interesting
colors that adds to red yellow, violet, orange, green, blue, brown and combinations
likem Yellow-brown to orange and red zircon are the popular occurrences. Blue is
the most popular, but it gets the color by heating of brown zircon. Due to pleochroism,
blue zircon looks greenish from certain angles. Medium dark, pure blue stones possess
the maximum value. Green zircon is hardly available and is expensive.
Clarity and Lustre - The clarity of zircon is from transparent
to translucent. Impurities results in various colors. Cat's eye chatoyancy zircon
is famous still very rare. Some crystals have radioactive elements of thorium as
well as uranium. With time, the radioactivity breaks down the crystal structure
so that such stones are closer to amorphous structure having less luster as compared
to the crystalline form. Such examples of low green zircon rare and are highly valued
by gem collectors. They have no threat of radioactive heath. Zircon when polished
gives a brilliant and vitreous sheen.
Cut and Shape - The high birefringence of zircon makes it necessary
for the cutter to orient the table of the stone to the optic axis. Colorless stones
are most often brilliant cut. Colored stones are mainly available in brilliant or
emerald step cut. Round stones are provided a 'zircon cut' that is similar to a
standard round brilliant cut, still having an extra row of facets at the edges.
The famous shapes of the gemstone include ovals, fancy trillions, octagons (emeralds),
rounds and pears. Small melees are also popular.
Treatment - Many zircon stones are totally not treated. Some brown
varieties, available in Southeast Asia are heated to create colorless and blue zircon.
However the colors are not necessarily stable because of ultraviolet rays or sunlight
that results in the color loss or changes. Some colors are not changed like rose
and rose-orange zircon, and orange to orange-brown zircon. Sometime heat is given
to golden-yellow zircon.
Gemological Characteristics: