Chemical composition -- Zirconium silicate.
Color-- Colorless, blue, yellow, green, red, brown, orange.
Optics -- R.I. 1.78-2.01.
Durability -- Hardness 6-7.5.
Crystal structure -- Tetragonal.
Specific Gravity -- 3.9-4.8.
Sources -- Sri Lanka (Ceylon), Burma, Thailand, Australia, Cambodia.
Zircon , when properly cut, produces lively, brilliant gems. Before the advent of manmade diamond simulants, colorless zircon was often used as a substitute for diamond . Large, fine zircons are scarce. Reddish-brown stones are often heat-treated to produce blue, colorless, and golden yellow, and the color change is stable.