Finding Gem Characteristics

The gemologist often is handicapped in trying to determine gem characteristics. If the stone is mounted in some kind of jewelry setting, manipulation for tests is difficult. Owners frequently object to removing stones from their mountings since damage is possible. Even if the stone is not mounted, it is not practical to risk ruining the cut or polish by scratching, chipping, or removing a piece for testing. Every bit of damage reduces the value of the gem. Testing on cut stones is usually limited to nondestructive manipulation. Unfortunately, some of the best gem study techniques involve destruction of the sample. Destructive tests are carried out, then, on uncut gemstones. Among such tests are chemical analysis, X-ray structure determination, and Mohs' tests for hardness. Nondestructive tests include determination of refractive index, specific gravity, pleochroism, spectral pattern, and examination for any foreign inclusions in the stone.