Blue Medium
Saturday, September 24th, 2011Blue Medium
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Blue Zircon Gems
There are relatively few gemstone varieties with good hardness and brilliance that occur in the color blue. Sapphire is the most famous, and is found in the full range of blues, from the palest blue to blue-black. Blue topaz, produced by irradiating colorless topaz, is the most popular of all blue gemstones, since it is widely available at attractive prices and is found in light and medium-dark tones. Other choices in blue include tanzanite (violet blue) and aquamarine (light blue). Tourmaline and spinel can sometimes be found in blue, but only rarely.
The most brilliant blue gemstone is undoubtedly zircon, which has a higher refractive index than even sapphire, tanzanite or spinel. But zircon is not well known by the general public, who are apt to confuse it with cubic zirconia, a synthetic diamond simulant. Zircon is a natural mineral, zirconium silicate, and is found in a range of colors, including white, blue, yellow, orange, brown, rose and green.
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 to turn blue when heated. This is why most blue zircon comes from Cambodia or Burma.
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 refractivity, where the difference between the two refractive indices is unusually high. 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 looked blurred.
Though blue zircon is a reasonably hard gem, with a hardness on the Mohs scale of about 7 to 7.5, it is somewhat brittle and therefore sensitive to knocks and pressure. Zircon has the tendency to wear along facet edges. Its use in rings should therefore be limited to protective settings or occasional wear jewelry.
Blue zircon can be found in a range of blue tones from very pale to a saturated medium blue. Due to pleochroism, blue zircon can look slightly greenish when view from one direction.
About the Author
AJS Gems, Bangkok a leading online dealer in high quality gemstones, including zircon, Burma ruby, sapphire, spinel and tourmaline. Blue Zircon Photos
