***Top quality gem blue zircons over 10 carats trade at a minimum price of $200 per carat and go up from there depending on the size of the stone and the quality of the color. Blue zircon, the most popular color, is produced by heat treatment of brown zircon. But not all brown zircon will turn blue when heated; only some zircon has the right physical structure for this to occur. This is why most blue zircon comes from certain sources in Cambodia or Burma. Blue zircon is a reasonably hard gem with a Mohs hardness of about 7 to 7.5. Blue zircon has some unique properties that make it very popular with gemstone aficionados. Not only does zircon have outstanding brilliance, but it also has very strong dispersion or fire, the tendency to split white light into the spectral colors. Zircon also has very pronounced birefringence or double refraction, with a wide variance between the two refractive indices. This can be often be observed with the naked eye when you look down through the table of a cut zircon; you will observe facet doubling that makes the facet edges appear blurred.