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Postage stamps dedicated to Zircon!
image location - stampmin.home.att.net |
Zircon is best known for its high refractive index, high dispersion, and high luster. One of
the key properties for identifying zircon is the high birefringence, which will cause the
pavilion facets to appear doubled. Prior to modern synthetics such as cubic zirconia,
colorless zircon was the stone of choice as a diamond simulant. Gem-quality zircon is normally
brown, but blue, orange, black, pink, green, yellow and colorless stones are also found in
nature. Zircon may contain up to 20% of the elements hafnium, yttrium or uranium. These stones
are mildly radioactive, and have often become metaminct, which means that their crystalline
structure has been broken down due to radioactive decay. Most zircon is heat treated to
improve the color, and this treatment can also restore the crystal structure in stones that
have decayed due to radiation. Radioactive Zircon that has undergone the metamiction process
is occasionally called "Low Zircon", while stable Zircon with an intact crystal lattice is
known as "High Zircon".
Most gemstone grade Zircon is from placer deposits, in the form of rounded, waterworn
pebbles. The gem gravels of Thailand are the most important commercial, followed by deposits
from Myanmar and Sri Lanka. Cambodia, Laos, and Vietnam also produce zircon as a byproduct of
corundum mining. Norway, Germany and Russia produce lesser amounts. Madagascar and Brazil
have produced some very large crystals and Canada and the United States also have small gem
grade zircon deposits. The world's most important deposits of industrial grade zircon are in
the heavy sands of Queensland, Australia followed by deposits in the United States and South
Africa. Industrial grade zircon is a $900 million industry. The ceramic industry uses
approximately 55% of the zircon sand produced and an additional 35% is used in the refractory
and foundry industries.
| Composition | ZrSiO4 | Class | nesosilicate |
| Specific gravity | Low 3.9 - 4.1 / High 4.65 - 4.80 | Refractive Index | 1.92 to 2.01 |
| Birefringence | weak (.002 - .059) | Pleochroism | mixed |
| Cleavage | indistinct | Fracture | conchoidal, brittle |
| Luster | adamantine | Transparency | transparent to translucent |
| Streak | white | Fluorescence | weak |
| Crystal system | Tetragonal | Twinning | Occasional |
| Hardness | 6.5 to 7.5 | Dispersion | .039 |
| Color | brown, red, yellow, green, blue, black, and colorless |
| Crystal habit | tetragonal prism terminated with four sided pyramids at each end. The prism may be lacking and the crystal can look octahedral. More complex crystals have faces of a less steeply inclined prism that taper the terminations. Also a secondary prism may truncate the primary prism by cutting off its edges and producing an octagonal cross-section through the crystal |
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Zircon is an accessory mineral in igneous and metamorphic rock, with crystals reaching large
sizes in mafic pegmatites and carbonatites. Because of its durability, it is often found far
from its source in sedementary rocks and alluvial heavy-mineral sands.
Named from the Arabic zar, gold, plus gun, colored, referring to one of the many colors that
the mineral may display. Because of its association with radioactive elements it is often used
in radiometric dating. The oldest object to be discovered on Earth is a tiny grain of Zircon,
4.3 billion years old.
Zircon is a stone of purity and innocence. It balances the emotions and enhances self esteem
and unity. It was used as an amulet by travelers to protect against accident and injury on the
journey. Zircon was believed to provide the wearer with wisdom, honor and riches, and it was
also used to stop the wearer from being stuck by lightening. The lost of luster on a Zircon
stone is said to warn of danger. Hindu poets tell of the Kalpa Tree, the ultimate gift to the
gods, which was a glowing tree covered with gemstone fruit with leaves of zircon. In the
Middle Ages, zircon was said to aid sleep, bring prosperity, and promote honor and wisdom in
its owner.