Emerald: a gem that became a reference color all over the world, who doesn’t know the lively and bright ‘emerald green’? From the pre-Columbian Mesoamerican and South American civilizations, to the ancient Egypt till the modern time, emerald has in any case occupied a special place in our hearts, it has always been the green gem par excellence.
When GIG Laboratory analyses an emerald, it focuses on every aspect of the gem in order to clearly declare if it is natural or synthetic, treated or untreated and, if treated, describes the type of treatment. All the analyses are performed in the most delicate way, being the emerald a fairly hard gem (6½-7 in Mohs scale), but also fairly fragile due to the fractures of genetic origin usually present in this gemstone.
As for all the colored stones, as soon as an emerald oversteps the check-in procedures and enter in the laboratory, it is photographed. Afterwards it passes on the gemologists desks who start describing the shape, the cutting style, the transparency and the color of the gem. Then they proceed measuring, weighting and calculating the specific gravity. To be as accurate as possible, the measurements are taken using an optical high-resolution measuring system, equipped with a digital camera for the 3D modeling of the stone and interchangeable optical lenses for various stone sizes. The weight is detected basing on a very sensitive and precise electronic scale with 5 decimal places and the specific gravity is calculated using a hydrostatic scale. The reaction at the polariscope, the refractive index, the pleochroism, long-wave (366 nm) and short-wave (254 nm) UV fluorescence and the absorption spectrum with a manual spectroscope, are then analysed.
All the data collected by the gemologists since this moment, allowed to understand if the green gem is really an emerald or if it is some type of simulant. The refractive index and the specific gravity can help separating between natural or hydrothermal synthetic vs flux synthetic emerald. The following analyses of inclusions using a binocular stereoscopic microscope is essential to determine if the emerald is natural, if it is treated, the geographical origin and will guide the advanced analyses.
If there are possibilities that the emerald is synthetic, to confirm it with no any margin of error, it is necessary to perform a chemical characterization with an Energy Dispersive X-Ray Fluorescence (ED-XRF) analyses, which will reveal the presence of elements such as for example Chlorine, Copper, Gold or other heavy elements, typical of emeralds grown by man in laboratory.
If the emerald is natural, it is necessary to check if it is treated. The typical treatment made on emeralds is the fracture filling. As previously mentioned, due to their genetic processes, emeralds are very often fractured. The fractures interrupt the passage of the light through the gem and this cause translucency or opacity. To let the light pass through the emerald in the best way possible, typically the fractures are filled with various substances, increasing the transparency of the gem. Fractures can typically be filled with oils, with resins or with a mixture of oil and resin. The analysis of the substances present inside the fractures, are performed with different instruments. First of all, the laboratory carries out an accurate observation with the microscope. Basing on this, are performed the Fourier-Transform Infrared spectroscopy (FTIR) analyses, applying a micro-system transmittance combination with the micro-Raman spectroscopy. Indeed, both techniques allow to focus the analyses on a single specific fracture, thanks to the microscopes coupled with the spectroscopes. All these advanced analyses are aimed at identifying exactly the types of materials present in the fractures and their quantity. In the Report will be declared both, the type and also the quantity of substance/s that fill/s the fractures, following the international nomenclature to describe it.
If the geographical origin opinion of the emerald is required, it is necessary to perform more analyses. The first one is always a meticulous observation of the inclusions with the microscope. To identify exactly the mineralogical phases of the crystalline inclusions, then it’s very useful the micro-Raman spectroscopy. In the micro-Raman system, the spectrometer works coupled with an optical microscope in confocal mode and it provides, without any sample preparation and in a completely non-destructive way, the spectroscopical features of the sample, basing upon the interaction of a laser source with the chemical bonds of the material it is pointed on. Not less important are the UltraViolet-Visible/Near InfraRed (UV-Vis/NIR) spectroscopy analyses, thanks to which it is possible to detect the absorption of diagnostical chemical elements such as Iron and Vanadium, and the chemical characterization performed with the Energy Dispersive X-Ray Fluorescence (ED-XRF). With the last one it is possible to detect the presence and the ratios of elements such as Chromium, Vanadium, Iron, Cesium, Rubidium and many others. It’s only collecting and studying all the data acquired by all the instruments that it is possible to give an opinion concerning the geographic origin. It is a long and quite complex work.
The main information arose from all the analyses performed, are finally reported on the GIG Colored Stones Report, where you will find clearly specified whether the emerald is natural or synthetic, if it’s treated or untreated and, if present, also the quantity and the type of substance in the fractures. Upon request, it’s stated also the geographical origin is also indicated.