Emeralds from various regions of Pakistan (Chitral, Swat and Khaltaro) and Afghanistan were compared and thanks to their unique characteristics it has been concluded that they could provide clues to determine the geographic origin of emeralds. The emeralds were analyzed with various types of spectrometer and those from Chitral were found to have distinguishing features.
First let’s discuss the various instruments which were used to analyze the emeralds:
(Spectroscopy: the study of the absorption and emission of light and other radiation by matter. It involves the splitting of light into its constituent wavelengths (a spectrum), in much the same way as a prism splits light into a rainbow of colours [www.atascientific.com.au].)
Raman spectroscopy: a non-destructive chemical analysis technique which provides detailed information about chemical structure, phase and polymorphy, crystallinity and molecular interactions, as well as contamination and impurity. It is possible to couple a Raman spectrometer to a standard optical microscope, allowing high magnification visualization of a sample [www.horiba.com].
FTIR (Fourier Transform Infrared Spectroscopy): a technology for acquiring emission spectra or infrared absorption from solid, liquid or gas samples. It is a form of vibrational spectroscopy that is useful in the study of a variety of soil chemical processes [www.sciencedirect.com].
UV-Vis-NIR (UltraViolet–Visible–NearInfraRed): a technique used to determine the optical properties (reflectance, absorbance, and transmittance) of liquids and solids. It is frequently used in a wide range of applications including pharmaceutical, food and beverage, chemical, education, etc. [www.shimadzu.com].
EPMA (Electron Probe Microanalysis): a technique used for quantitative analysis of the elemental composition of solid specimens at a micrometer scale. The method uses bombardment of the specimen by keV electrons (kilo electron volt = 1000 electron volts, used to measure kinetic energy) to excite characteristic X-rays from the sample, which are then detected by using wavelength-dispersive (WD) spectrometers [www.sciencedirect.com].
LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass): a technique using a pulsed laser source and considered one of the most versatile methods for the compositional analysis of solid materials due to its sensitivity and conceptual simplicity. It has become a widespread method capable for the element- and isotope-selective analyses of various materials [www.sciencedirect.com].
Now that we know a little more about the terminology and techniques used to analyze the materials (see Encyclopedia of Spectroscopy and Spectrometry at [www.sciencedirect.com] to know more), we can discuss the conclusion that were drawn from the analyses. It was seen that the emeralds from Chitral had unique characteristics, in that they did not have three-phase inclusions (refers to the three phases of matter: solid, liquid, and gas – an emerald can e.g. include a gas bubble and crystals of a different material), a considerable Fe2+ (a form of iron, Fe = Ferrum, the latin word for iron) absorption determined by the UV-Vis-NIR spectrometer. Absorption spectra are used to determine the presence of a particular substance and to quantify the amount of the substance present. The analyses also revealed a high presence of Cs (Cesium) and Li (Lithium). These findings are important as they might be used to provide clues to determine the geographical origin of emeralds. It is known for example, that emeralds from Colombia almost always have three-phase inclusions and this has been used as an indicator of their geographical origins (see GIA’s article about this: Three-Phase Inclusions in Emerald and Their Impact on Origin Determination, Gems & Gemology, Summer 2014, Vol. 50, No. 2).
In conclusion, the reality is that the gemstone industry is beginning to rely on gemological laboratories to provide origin determination for not only emeralds, but other precious stones as well (Geographic Origin Determination Of Emerald, Gems & Gemology, Winter 2019). Perhaps this can be used for diamond as well?
[Inspired by an article in the Journal of Gemology Vol. 38 (No.6) 2023 by Carina S. Hanser, Tom Stephan, Bilal Gul, Tobias Häger and Roman Botcharnikov]