Gemology

The Gemology, also science of gemstones or short Gemology ( sporadically Gemnologie ), is engaged as a branch of mineralogy used exclusively as precious stones ( gems ) minerals and varieties and their synthetics and imitations. With esoteric meaning of stones, medicine and the like, the Gemology has nothing to do.

In a gemological examination of a stone, three questions must be answered:

All analyzes are carried out using non-destructive methods since you are working in gemology often with world-class gems. Unlike in geology no sample for analysis can be used. Instead, the blocks need to be identified by their optical, physical, chemical, and crystallographic properties. Quantitative data and qualitative data can be obtained. Thus, e.g. a precious stone in accordance with the crystal systems are classified, or a refraction index can be read.

In practice, the expertise of a neutral laboratory can be obtained only in special cases. Analysis and assessment must be made possible on the spot, for example, the gem trade. Therefore professional gemologist and gemstone buyers use mobile laboratories, which summarize all the necessary equipment in a carrying case. So-called travel laboratories even have their own power supply, so they are independent of any external infrastructure. They are also suitable for gemological expeditions.

The title gemstone specialist / f is an additional qualification for Gold, silversmiths and gem cutters. But also relevant experts from the banking and mortgage lending industry to attend appropriate training courses of national gemological societies.

The International Centre of gemologists is Amsterdam in the Netherlands.

Optical analysis of Gemmology

Gemstones are usually transparent minerals. Therefore, Optical investigation methods play an important role in the nondestructive analysis. After the first observation with a magnifying glass inclusions and surface properties are examined microscopically. Gemological Microscopes Stereo Microscopes are a small to medium magnification ( total magnification of < 10 to about 100). They must have a large depth of field, as three-dimensional objects are studied. The consideration of the object must be possible in the dark field, transmitted and reflected light. As a light source a cold-light source is used that does not increase even after prolonged viewing the temperature of the stone. For certain studies, for example, to detect imitations, precious stones are immersed in an immersion liquid and examined microscopically in transmitted light. Before and behind the brick further optical elements such as polarization filters can be arranged.

An easy to perform optical analysis technique is the determination of the refractive index. Each mineral has a specific value, which depends on the material and crystal structure. Gems with high refractive index are particularly brilliant in general - for example, a diamond has a refractive index of 2.4, the quartz is about 1.55. The refractive index can be measured easily and accurately with a refractometer. Optical Gemstone are compact, autonomous instruments that can be carried easily. The examination is carried out in the light of the sodium D line (589 nm ), which is filtered with a filter from the sodium light. Owing to the high refractive indices of the test object gemstones is placed on the prism of the refractometer with a drop of a high refractive index as mentioned Anderson solution ( for example diiodomethane ), which extends the measurement range.

Wherein the optically anisotropic precious stones such as sapphire or ruby ​​, a polarization filter is placed on the eyepiece of the refractometer to measure the difference in the refractive indices of the birefringent tiles. With a Gemstone most stones can be assessed with a smooth or round polished surface. It is the professional tool of choice to detect synthetic and other low -priced stones safely.

For more detailed study of birefringent stones a polariscope is used. When rotating the analyzer birefringence and stress anomalies are easily recognizable. To measure the optical axis of a Konoskoplinse is placed between the object and analyzer. The position of the optical axis allows conclusions on the crystal structure. This also allows for viewing by a Dichroscope not be visible on the stresses in the crystal structure.

Information on the material of a gemstone are in addition to the refraction measurement spectroscopy. On the basis of absorption lines in the spectrum of the light shining through the stone, its components can be determined. For use are instruments that work with a vision prism Amici, as they have very compact dimensions.

Besides the optical response of gemstones in the visible light and the observation in the ultraviolet light of different wavelengths is important. In this case, artificial and falsified stones are detected. Thus, for example natural sapphires no fluorescence, synthetic and heat-treated, however, have unique luminous phenomena in ultraviolet radiation of different wavelength.