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Home > Gemstones > Gem Identification
Gem Identification

Equip your self with helpful information on tools and techniques equipped by Gemologists for identifying genuine gemstones.

Binocular MicroscopeAt one hand where some gemstones are readily identified on sight, many of them are quite similar in appearance and cannot unfailingly be identified on visual appearance alone. The tools used by gemologists for the identification and grading of different gemstones, vary from the common ones to the high-tech ones. A few basic tools can recognize most gemstones that every gemologist should have at hand. Often, a single test is not convincing, and a gemologist often needs to carry out several different tests to achieve an affirmative identification.

One of the most functional tool for gemologists is the binocular microscope. Simple models are obtained with better scopes with enhanced accessories. These scopes provide both light field (lighting from below) and dark field (lighting from the side) views and usually have a magnification range from 10X to perhaps 100-200X. Magnifications of 10X to 40X are most often used, but the higher range is occasionally needed for careful inspection of inclusions.

Another required tool by gemologists is the refractometer. A small drop of liquid with a high refractive index (RI) is placed on a glass cylinder in the top of the refractometer and illuminated from a separate light source. The RI is then read from a magnified gauge on the front of the refractometer.

The polariscope has two polarizing filters and a light source below. As the upper filter is rotated, it allows a varying amount of light to pass through the system. A transparent gemstone held and turned between the crossed filters shows different patterns of light, depending on its optic character, and this can often be used to differentiate between different gemstones with similar appearance.

A Chelsea filter, also known as emerald filter, is sometimes useful in distinguishing between natural and synthetic emeralds or between aquamarine and blue topaz, but its usefulness and reliability are limited, so it has declined significantly in importance.

The spectroscope is sometimes used to part natural from synthetic gem materials, as variations in chemical composition can be revealed in the absorption spectrum of light transmitted through the stone. These instruments can be quite simple, as shown here, or much more elaborate. The average gemologist is unlikely to use this very often.

An ultraviolet (UV) light source, or black light, will reveal fluorescent action in many gem materials, and this can help to identify many stones.

Gemologists very seldom use hardness points, intended to test the scratch resistance or hardness of a material, because they are by nature destructive. Occasionally, a gemologist will endeavor a very small scratch in an inconspicuous area of an object, such as a sculpture, but such tests should never be used until other tests are exhausted, and a faceted stone should never be subjected to a hardness test.

Sets of several liquids of known specific gravity (SG) are sometimes used to distinguish between various materials that closely match in other characteristics. As the substrate of SG liquids evaporates, the SG changes, so such test sets must be recalibrated periodically. Specific gravity can also be tested on weight scales by comparing the weight of an object immersed in water with the weight of the object in air. Another test often used to distinguish amber from its substitutes is simple captivation in a saturated salt solution; amber floats in salt water, but most of its imitations sink.

X-ray photographs are now and then used, as in the separation of natural pearls from cultured pearls, and x-ray diffraction techniques are occasionally used in advanced laboratories.

A heated point can be used to separate some organic materials from their substitutes. For example, a hot point will elicit a sweet resinous smell from amber but an acrid smell from plastic.

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