Zircon

Specific Gravity: 4.69
Refractive Index: 1.93-1.98
Birefringence (DR): 0.059
Luster: Resinous to adamantine
Crystal Structure: Tetragonal
Composition: Zirconium silicate
Hardness: 7½

Zircon is most famous for its colorless stones. These resemble diamonds and have been used both intentionally and mistakenly in their place. Although colorless when pure, impurities will produce orange, yellow, blue, brown, red, and green varieties.

Brown stones from Thailand, Kampuchea, and Vietnam are usually heated to change them into the colorless or blue stones commonly used in jewelry. Blue stones that revert to brown will regain the blue if heated. Blue zircon reheated in the presence of oxygen will change to golden-yellow.

Zircon may be distinguished from diamond by its double refraction and by wear and tear on its facet edges. It has been imitated by both colorless glass and synthetic spinel. Some zircon contains radioactive thorium and uranium, which eventually break down the crystal structure.

The green stones are often decayed ‘low’ zircons. On the other hand, a ‘metamict’ structure is an undamaged and is called a ‘high’ ziron. It is common to find waterworn pebbles with polished surface. Golden-brown is one of the most popular

Zircon was believed to provide the wearer with wisdom, honor, riches, and loss of luster was said to warn of danger. The name is from the Arabic zargun, which derives from the Persian for ‘gold color.’

Zircon crystal occurs with double, pyramidal ends. Its surface has square cross-section. It has a high birefringence, luster, hardness, and a wide color range. That makes it an ideal stone to be used in jewelry. However, cut stones are somewhat brittle and are susceptible to damage if not treated with care.

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Occurrence

Gem-quality crystals are usually found as pebbles in alluvial deposits. Sri Lanka has been a source of gem material for over 2,000 years. Other localities include Thailand, Myanmar (Burma), France, Tanzania, Nigeria, Brazil, Australia, Kampuchea, Vietnam, and Cambodia.