Zircon is a mineral that belongs to the group of non-silicates and is a source of zirconium metal. Its chemical name is zirconium silicate, and the corresponding chemical formula is ZrSiO4. Zircon precipitates from silicate melts and has relatively high concentrations of incompatible high-field 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 color of zircon varies between colorless, golden yellow, red, brown, blue and green.
The name derives from the Persian zargun, meaning "golden hue". This word is changed to "jargoon", a term applied to light colored 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 favored for its high specific gravity (between 4.2 and 4.86) and adamantine luster. Due to its high refractive index (1.92), it has sometimes been used as a substitute for diamond, although it does not exhibit quite the same play of color as a diamond. Zircon is the heaviest of the gemstones, it sinks easily even in very viscous liquids. The Mohs hardness is between that of quartz and topaz, at 7.5 on the 10-point scale, although below that of the similar artificial zirconia stone. Zircons can sometimes lose their inherent color after prolonged exposure to strong sunlight, which is unusual in a gemstone. It is immune to acid attack except sulfuric acid and only when ground to a fine powder.
The value of a zircon gemstone depends largely on its color, clarity and size. Before World War II, blue zircons (the most valuable color) were available from many gem 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! Do not confuse natural zircon with cubic zirconia, popularly known as "zirconium", which is a stone created in the laboratory and with which natural zircon has only the similarity of the name.