Zircon
Zircon has been known since antiquity. The name derives from the Arabic word 'Zargun', meaning 'golden color'. Zircon has high refractive index and strong dispersion, it has great brilliance and intensive fire. It is brittle and therefore sensitive to knocks and pressure; the edges are easily damaged. Zircon often contains traces of radioactive (uranium, thorium) elements in its structure. Which causes it to be metamict. The unstable form of Zircon is called Cyrtolite. It is dull or pitchy in luster. When it is heated the metamict Zircon crystals become stable and change into normal crystal structure. Radioactive Zircon that has undergone a metamiction process is called low zircon, and stable Zircon with a intact crystal latice is called 'High Zircon'. The dark brown to black color observed in most Zircon crystals is caused from iron oxide impurities. The green color Zircon usually indicates the zircon is radioactive variety. The green slightly radioactive Zircons are rarely found in the gemstone trade. Zircon is a source of the metal Zirconium, which took its name from the mineral and is now used in the production of nuclear reactors.
Gem-quality zircon crystals have an adamantine luster and are normally found as pebbles in alluvial deposits. Reddish-brown varieties have been called hyacinth or jacinth. Gem-quality Zircon can be found in a number of colors. Impurities produce blue, red, brown, green, yellow and orange varieties. It can also be heat treated to create a variety of colors.
DEPOSITS
Zircon is widely distributed. Pailin, western cambodia,is the best source for gem-quality blue zircon. Other top sites for high-quality Zircon gems include the Mogok mines in Mandalay, Central, Burma (Myanmar), Ratnapura, Sri-Lanka and Kanchanburi, Thailand, well-formed red crystals come from the Auvergne, France. Brown crystal are found at Arendal Norway and near white rolled pebbles exist in Tanzania.
Properties
| Species | ZIRCON |
|---|---|
| Variety | Zircon |
| Chem. Comp | Zr SIO4 (Silicate of zirconium) |
| Crystal System | Tetragonal |
| Habit | Prismatic |
| Color | Colorless, blue, Orange, Red, Yellow, Golden Brown, Green and Shades of green. |
| Cause of COLOR | Red -(niobium) Nb 4+ Color centre green. Blue - uranium |
| Luster | Subadamantine |
| Hardness | 7 to 7.5 Low Type 3.90 to 4.10, High Type 7 to 7.5 |
| S.G. | Low Type 3.90 to 4.1, High Type 4.67 to 4.70 |
| Optic Sign | U +ve |
| R.I. Range | Low Type 1.790 to 1.810, High Type 1.925 to 1.984 |
INCLUSIONS
Needle like inclusions, crystal, Zoning.
SIMULANTS
Simulants of Zircon comes in a variety of form such as Tourmaline, Garnet, Quartz, Synthetic Spinel, sphene, diamond, blende.
