Gem materials are grouped into five categories: 1) Genuine natural gemstones, 2) imitation gemstones, 3) treated gemstones, 4) synthetic gemstones and 5) artificial gemstones. Diagnostic properties in identif icating and discriminating gem materials of the same species are due to the differences in crystal growth processes and conditions among gemstones of different categories. Crystallography, particularly science of crystal growth, may play important roles in this respect.
