Zircon is most famous for colourless stones, which closely resemble diamonds and have been used both intentionally and mistakenly in their place. Although colourless when pure, impurities will produce yellow, orange, blue, red, brown, and green varieties. Brown stones from Thailand, Vietnam, and Kampuchea are usually heat-treated to change them into the colourless or blue stones popular in jewellery. Blue stones that revert to brown will regain the blue if reheated. 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 colourless glass and synthetic spinel. Some zircon contains radioactive thorium and uranium, which eventually break down the crystal structure. Decayed stones are known as”low” zircon, with a”metamict” structure; undamaged material is”high” zircon.
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 Burma, Thailand, Cambodia, Vietnam, Kampuchea, Australia, Brazil, Nigeria Tanzania, and France
|Colour||White, black, gray, yellow, orange, pink, lavender, green, blue|
|Luster||Resinous to Adamantine|
|Refractive Index||1.93 to 1.98|