With further post-graduate training and experience they can qualify as appraisers (valuers). There are numerous professional schools and associations of gemologists and certification programs all over the world.
Some gemologists specialize in various gemstones, such as diamonds or emeralds. The laboratory gemologists are expert in identification of origin.
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.
Gemstones are basically categorized based on of their crystal structure, specific gravity, refractive index, and other optical properties, such as pleochroism. The physical property of "hardness" is defined by the non-linear Mohs scale of mineral hardness.
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 included partially melted exogenous crystals to demonstrate evidence of heat treatment to enhance colour.
The spectroscopic analysis of cut gemstones also allows a gemologist to understand the atomic 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 polished colour. Initially, the stone is identified by its colour, refractive index, optical character, specific gravity, and examination of internal characteristics under magnification.
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