Zircon is a kind of island structure silicate mineral and its chemical formula is Zr[SiO4]. Because the zircon contains the radioactive element like U, Th etc., they can make changes of the crystalline structure of the zircon and cause the apparent changes of various physical properties. So in gemology, according to the degree the effects caused by the radioactive element in the zircon to refractive index, hardness and relative density, we can divide it into the three styles: High Style, Middle Style and Low Style. Generally speaking, the zircon used for gemstone belongs to the High Style, least affected by the radiation, the refractive index, hardness and relative density are the highest among the three styles, so it is called the High Style and it also has strong birefringence and complete crystal form. Some green transparent Low Style Zircon can also be used as the gemstone.

The colors of zircon are various, including colorless, yellow, light red, orange, brown, red brown, yellow green, leaf green, dark green and sky blue etc. It has corundum luster, transparent to semi-transparent, refractive index of High Style is 1.90 – 1.94 to 1.95 – 2.01; Low Style is 1.78 – 1.783 to 1.81 – 1.815, High Style of birefringence is 0.059; Low Style is 0.005. High Style zircon has strong dispersion, it usually is 0.04 and it is often used as the substitute of diamond due to its strong dispersion.

The crystalline form of zircon, which belongs to tetragonal system, often takes on four square column shape and four square double cone. It has developmental shells shape fracture, High Style of relative density is 4.6 – 4.8, Low Style is 3.9 – 4.1. High Style of Mohs Hardness is 7 – 7.5, Low Style is 6 – 6.5. It has strong fragility, which means that its small surface edge is easily damaged. If the loose-packed zircons rub each other into the packing paper, they will be worn down. Because of this reason, before we pack them with packing paper, we use soft paper to pack them well individually and pack them together finally.

The zircon is common as a kind of auxiliary mineral in the magmatic rock and widely distributed. But the zircons of gemstone level are mainly originated in Sir Lanka, Myanmar, Cambodia and Australia and so on.

We need to emphasize here that though there is radioactive element in the zircon, due to its tiny content, it has no harm to our health. At the same time, the zircon is regarded as the symbol of success and people consider it as the birthstone of December.
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