Gemology is the science, art and profession of identifying and evaluating gemstones. It may be considered a branch of mineralogy. Some jewelers are gemologists and are qualified to identify gems.
With further training they can become appraisers (valuers). There are professional schools and associations of gemologists and certification programs.
Some gemologists specialize in various gemstones, such as diamonds or emeralds. Such specialists are found in fields in which a great deal of knowledge is required, especially in the determination of exceptionally "pure" gems.
Recently, the demand for gemological services has grown, as increasing quantities of synthetic gems such as cubic zirconia and synthetic moissanite are manufactured. Gemologists perform such work as the identification of synthetic and natural gemstones, fracture-filled gemstones, and color-enhanced or treated natural gemstones. Gemology in the 21st century has become a rigorous science where constant study is necessary for correct identifications.
Gemstones are basically catogorized based on its crystal structure, specific gravity, refractive index and other optical properties.
Gemologists study these factors while valuing or appraising cut and polished gemstones. Gemological microscopic study of the internal structure is used to determine whether a gem is synthetic or natural by revealing natural fluid inclusions and evidence of treatments to enhance color.
The spectrum analysis of cut gemstones also allows a gemologist to understand the chemical structure and identify its origin as it is a major factor in valuing a gemstone.
For example a ruby from Burma will have definite internal and optical activity variance as compared to a Thai ruby.
When the gemstones are in a rough state, the gemologist studies the external structure; the host rock and mineral association; and natural and polisihed color. Initially the stone is identified by its color, specific gravity and its place of origin.