People often email us photos of gemstones and ask us for help in identifying their stones. We try to be helpful, but even the best gemologist in the world can't definitively identify a gemstone from a photograph. Even visual inspection of the actual gemstone is rarely sufficient.
The systematic study of gemstones has come a long way since the days when any attractive red stone was called a ruby. Today gemologists have to be able to identify over 200 different varieties of gemstones, as well as detect an ever-growing list of gem treatments and synthetics. What once was an art has become a science and gemstone identification without careful measurement is just guesswork.
Every type of gemstone has a unique set of physical and optical properties. These include not only color and luster, but also hardness, specific gravity or density, and refractive index. Though several type of gemstones may have approximately the same specific gravity or the same specific refractive index, each gem type has a unique profile when results of all the basic tests are considered. Just don't try to identify a gem by refractive index alone! You could very easily be wrong.
The basic gemological tools are not difficult to learn to use. They include the simple 10x loupe (a powerful tool in the hands of an expert), the refractometer (for measuring refractive index), the polariscope (for identifying singly and doubly refractive gems), and a scale accurate to the 1/100th of a carat (for measuring specific gravity).
The binocular microscope is an increasingly important tool. It can be used reliably to detect signs of heat treatment or fracture filling, for example, though considerable skill and experience is required. Some forms of treatment can only be detected by specialized and expensive equipment. Detecting radiation treatment requires use of gamma ray spectroscopy, and beryllium treatment of sapphire is most reliably detected with a procedure known as LIBS (Laser Induced Breakdown Spectroscopy). You're unlikely to find these tools at your neighborhood gemologist.
A well-trained gemologist with vast experience in a particular kind of gem can often provide very detailed information about a gemstone, including information about its specific origin. But this sort of informed judgement about origin needs to be distinguished from the quantitative tests that yield definitive conclusions about the type of gemstone. This is usually reflected in the certificates issued by gemology labs. While the lab can conclusively identify the material as ruby (corundum); it can say only that the observed characteristics are consistent with the material being mined in Madagascar. Gemology has become a science, but there's still some art left in it.
- First Published: January-10-2008
- Last Updated: October-06-2010
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