Many minerals are colorless in their purest state. Anything with a hardness the same as or greater than glass (5 to 6 on the Mohs hardness scale) can scratch glass. Therefore, other gemological tests must be performed to confirm identification. You can submit your stone to GIA for identification or have a local gemologist help you identify the stone.
Fluorescence is the visible light some gemstones emit when they are exposed to invisible ultraviolet (UV) rays. In natural diamonds, blue is the most common color of fluorescence, but other colors may be visible. On a IGL Diamond Grading Report, fluorescence refers to the strength, or intensity, of the diamond’s reaction to long-wave UV, which is an essential component of daylight.
In 2002, a coalition of governments, non-governmental organizations and the diamond industry established the Kimberley Process to control the export and import of rough diamonds to eliminate the trade in conflict diamonds. Today 99% of diamonds in the marketplace are conflict-free.
IGL uses a standard set of lighting conditions for the color grading of all diamonds. The light source used is designed to simulate natural sunlight, which contains a component of ultraviolet radiation. In rare cases, a diamond can emit strong or very strong blue fluorescence when exposed to ultraviolet radiation—in such instances that fluorescence may temporarily and slightly affect its color appearance.
The number of facets affects the pattern of the reflections in a diamond rather than overall brightness. Diamonds with more facets have numerous smaller reflections instead of fewer larger reflections. Brightness is a function of proportions, polish and symmetry, not the number of facets.
Low zircon’s crystal structure has been altered by thousands of years of irradiation from its own trace elements. It’s typically dark green. High zircon’s gemological properties are higher, so type can be determined with standard gemological testing. Most zircon used in jewelry is high zircon.
Make sure your invoice specifies that the spinel you are buying is natural. If you have any doubt, a report from the IGL lab will confirm whether a spinel is natural.
The definition of padparadscha has always been debated. IGL has studied the history of the term and its modern use and indicates on a Colored Stone Identification & Origin Report when a sapphire, in our opinion, meets the criteria to be described as padparadscha.
IGLtourmaline reports include an opinion on geographic origin when it is possible to establish.
There is no official standard for Imperial topaz. Some dealers use the term for colors that are orange to pink to red to purple; others reserve the term for certain saturated shades. It’s the color, not the term “Imperial,” that gives topaz its value.