zircon

Zircon (including hyacinth or yellow zircon) is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is (Zr1-y, REEy)(SiO4)1-x(OH)4x-y.

Zircon forms in silicate melts with concentrated incompatible elements and accepts high field strength elements into its structure. For example, hafnium is almost always present in quantities ranging from 1 to 4%. The crystal structure of zircon is tetragonal crystal system.

The natural color of zircon varies between colorless, yellow-golden, red, brown, blue, and green.

Colorless specimens that show gem quality are a popular substitute for diamond; these specimens are also known as "Matura diamond".The name either derives from the Syriac word ܙܐܪܓܥܢܥ zargono, from the Arabic word zarqun (زرقون), meaning vermilion, or from the Persian zargun (زرگون), meaning golden-colored.

These words are corrupted into "jargoon", a term applied to light-colored zircons. The English word "Zircon" is derived from "Zirkon," which is the German adaption of these words.

Yellow zircon is called "hyacinth", from the flower hyacinthus, whose name is of Ancient Greek origin; in the Middle Ages all yellow stones of East Indian origin were called hyacinth, but today this term is restricted to the yellow zircons.Owing to their uranium and thorium content, some zircons may undergo metamictization.

The processes, related to internal radiation damage, partially disrupt the crystal structure and partly explain the highly-variable properties of zircon.

As zircon becomes more and more modified by internal radiation damage, the density decreases, the crystal structure is compromised, and the color changes.Zircon occurs in many different colors, including red, pink, brown, yellow, hazel, black, or colorless. The color of zircons sometimes can be changed by heat treatment.

Depending on the amount of heat applied, colorless, blue, and golden-yellow zircons can be made. In geological settings, the development of pink, red, and purple zircon occurs after hundreds of millions of years provided the crystal has sufficient trace elements to produce color centers.

Color in this red or pink series is annealed in geological conditions above the temperature about 350oC.