Gemology

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Gemology (gemmology outside the United States) 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 categorized based on of its crystal structure, specific gravity, refractive index and other optical properties.

Gemmologists study these factors while valuing or appraising cut and polished gemstones. Gemmological 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 colour.

The spectrum analysis of cut gemstones also allows a gemmologist 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 gemmologist studies the external structure; the host rock and mineral association; and natural and polisihed colour. Initially the stone is identified by its colour, specific gravity and its place of origin.

1 General Identification of gems
2 External links

[edit] General Identification of gems

There are many courses and programs that offer very specific education on gem grading and identification. It can be quite the complex science. Any single method is not 100% accurate as well. For example, the specific gravity of ruby is 3.97-4.08, glass is 3.15-4.20, and cubic zirconia is 5.6-5.9. So, one can easily tell the difference between cubic zirconia and the other two; however, there is overlap between ruby and glass.

[edit] Identification by refractive index

One method to determine the type of gem is to measure the refraction of light in the gem. Every material has a critical angle, at which point light is reflected back internally. This can be measured and thus used to determine the gem. Typically this is measured using a refractometer although it is possible to measure it using a microscope.

[edit] Identification by specific gravity

Specific gravity, also known as relative density, is different depending upon the chemical composition and crystal structure type.

Specific Gravity is measured by comparing the weight of the gem in air with the weight of the gem suspended in water.

[edit] Identification by dispersion

This method uses a simiar principle to how a prism works to separate white light into the rainbow. Essentially when light passes from one medium to another it bends. Blue light bends more than red light. Depending upon the material will adjust how much this light bends. This can be measured and used to determine the materials.