Zircon is a mineral belonging to the non-silicate group and is a source of metallic zirconium. Its chemical name is zirconium silicate and its chemical formula is ZrSiO4. Zircon precipitates from silicate melts and has relatively high concentrations of high field incompatible elements. For example, hafnium is almost always present in amounts between 1 and 4%. The crystal structure of zircon is a tetragonal crystal system. The natural colour of zircon ranges from colourless, golden yellow, red, brown, blue and green.
The name derives from the Persian zargun, which means "golden hue". This word is changed to "jargoon", a term applied to light-coloured zircons. The English word "zircon" is derived from Zirkon, which is the German adaptation of this word. Yellow, orange and red zircon is also known as "hyacinth", from the hyacinthus flower, whose name is of ancient Greek origin.
Clear zircon is a well-known form of semi-precious gemstone, favoured for its high specific gravity (between 4.2 and 4.86) and adamantine lustre. Because of its high refractive index (1.92), it has sometimes been used as a substitute for diamond, although it does not have quite the same colour play as a diamond. Zircon is the heaviest of gemstones, sinking easily even in very viscous liquids. Mohs hardness is between that of quartz and topaz, at 7.5 on the 10-point scale, though below that of similar artificial zircon stones. Zircons can sometimes lose their inherent colour after prolonged exposure to strong sunlight, which is unusual in a gemstone. It is immune to acid attack, with the exception of sulfuric acid and only when ground to a fine powder.
The value of a zircon gemstone depends largely on its colour, clarity and size. Before World War II, blue zircons (the most valuable color) were available from many gemstone suppliers in sizes between 15 and 25 carats; since then, stones even as large as 10 carats have become very rare, especially in the most desirable color varieties.
Warning! Don't confuse natural zircon with cubic zirconia, popularly known as "zirconium", which is a laboratory-created stone that natural zircon bears only a passing resemblance to in name.