Clarity
A complication in grading colored stones arises from the fact that the absolute definition of the above grades varies with the type of gem material. The GIA breaks down colored gemstones into three classes depending upon the likelihood of a particular gem material being included. For example:
Type I colored stones include aquamarine, morganite, smoky quartz, topaz (blue, yellow, orange, pink, red), zircon (blue), and tanzanite. In the marketplace these gemstones are often virtually inclusion-free.
Type II colored stones include corundum (all colors), garnets (all species), iolite, peridot, quartz (amethyst, citrine, ametrine), spinel (all colors), tourmaline (blue, orange, yellow, parti-), and zircon (green, orange, red, yellow). In the marketplace these gemstones are usually included.
Type III colored stones include emerald, and tourmaline (red, pink, watermelon). In the marketplace these gemstones are almost always included.
By the above criteria, a VVS grade aquamarine (A Type I gem, often virtually inclusion-free) would contain only minute inclusions that would be difficult to see under 10X magnification and would be invisible to the unaided eye. A VVS grade rubellite tourmaline would be characterized by noticeable inclusions, easily seen under 10X magnification but barely visible to the unaided eye. Two different types of gemstones would each be classed VVS, but display visibly different degrees of inclusion! Depending upon the type of gemstone, other classes show a similar variation in definition of clarity grade.
|
