This is the name given to the relatively uncommon, green variety of corundum. In the nineteenth century it was also known as “oriental emerald," just as violet and yellow corundum were called "oriental amethyst" and "oriental topaz." These names stemmed from a scant knowledge of mineralogy among gem merchants and have now been abandoned.
Appearance Due to its iron content, green sapphire is generally quite a strong, bright green color, sometimes with green to bluish green or yellowish green pleochroism. Individual stones are sometimes cut at different angles from the rough crystal, to bring out the best color. The luster is very good, as with all corundum. The mixed, oval cut is the most common, but square or rectangular step cuts are also used. These gems are usually small to medium sized and rarely exceed a few carats.
Distinctive features The color is quite distinctive, especially combined with the particular luster of corundum.While green tourmaline can, at first glance, look fairly similar in color, it has more pronounced pleochroism, the direction corresponding to the bluer green often seeming rather opaque, and it is always, or nearly always, given a rectangular, step cut strictly aligned -to the elongated shape of the prism. Green zircon can be quite similar to green sapphire in both color and luster, but it has far less obvious pleochroism and sometimes much stronger bire fringence, easily detectable with a lens. Many green zircons, however, have weak or virtually nonexistent birefringence. In such cases, their density is also very similar to that of corundum, so the physical characteristics will need careful checking to establish a distinction.
Occurrence Green sapphire comes mainly from Australia, but it is also found in the United States (Montana) and Thailand.
Value‘ As for all forms of corundum except ruby and sapphire, its value is quite low. It is perhaps worth a bit more than yellow sapphire, due to its greater rarity and the difficulty of finding stones of any size.
Simulants and synthetics Not being widely known or appreciated, this stone is not often imitated. But green syn thetic corundum has occasionally been produced; it is of a brighter color than the natural mineral. Bluish green synthetic spinel has also been produced, whether to imitate green sapphire or zircon it’ is hard to say, as it bears little resemblance to either.