Blue Zircon Gemstones
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, which is produced by irradiating colorless or pale topaz, is the most popular of all blue gemstones, since it is widely available at affordable 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. Yet 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 called zirconium silicate that 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 for this to occur. This is why most blue zircon comes from certain sources in 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 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.
Although blue zircon is a reasonably hard gem, with a Mohs hardness 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 viewed from one direction.
- 初刊: 11月-10-2009
- 最終アップデート: 1月-23-2019
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