Thematic Articles

Corals and pearls are “organic gems” produced by living beings. These esthetic “biomineralizations” are attractive for their color and the optical effects resulting from their structure.

Treatment processes to improve the color, appearance, and/or durability of certain gemstones have been used for hundreds of years, and their variety, sophistication, and application within the jewelry trade have increased over the past several decades. Whether or not these enhancement processes are considered acceptable trade practices, their use must legally be disclosed at the time of gemstone sales. Disclosure of treatment information requires that treated gems be correctly identified by gemologists and gemtesting laboratories. Treatment detection is based upon careful documentation of the properties of gem materials, including the use of advanced nondestructive techniques for obtaining chemical and spectral data.

Synthetic gems are superlative examples of crystal growth. Today, industrial and scientific crystal growth is a highly sophisticated endeavor employing a wide range of methods. Many of these have been adapted to grow gems for jewelry use. Most major gemstones have been synthesized, and these products are commercially available around the world, often at a fraction of the cost of a natural gem of comparable size and quality. Distinguishing them from their natural equivalents involves a number of interesting challenges. Inclusions (internal features) observed by microscopy often provide conclusive proof of synthetic origin. When routine testing procedures (refractive index, specific gravity, fluorescence, and internal inclusions) do not provide sufficient evidence, laboratories must employ more advanced analytical instrumentation.

Identifying faceted gemstones involves practices that are closely related to the classical determinative methods used by mineralogists. Measurements of optical and physical properties, combined with acute observation using various illumination techniques, are usually sufficient to determine the nature of a gem. Determining the geographic origin of a gem or the enhancement treatments it was subjected to, however, can require the expertise of an experienced gemologist and a combination of spectroscopic laboratory techniques.

In colored gems, minor and trace chemical components commonly determine the difference between a common mineral specimen and a gemstone. Also, these components are often responsible for the color, and may provide a “fingerprint” for determining the provenance of the gemstone. The minor elements that are incorporated will depend on local geologic conditions such as temperature, redox conditions, and, particularly, chemistry.

The geology of gem deposits is a relatively new area of research focused on understanding the rare and exceptional geologic conditions that give rise to gem-quality materials. These conditions may include the availability of sometimes uncommon major constituents, the presence of adequate chromophores, limited concentrations of undesirable elements, open space, an environment conducive to forming crystals of sufficient size and transparency, and a favorable environment for mining. Future research should aid exploration, which until recently has been nonsystematic and nonexistent for many gem minerals, with diamond as the notable exception.