Advanced Gemstone Analysis
Not very long ago, gemstone identification was carried out with a small set of instruments used to measure properties such as refractive index and specific gravity. Experienced gemologists could identify nearly every kind of gem with just a refractometer, a polariscope, a set of specific gravity liquids, a spectroscope and a binocular microscope.
With the introduction of new synthetics and treatments, as well as a significant increase in the number of gem varieties in the marketplace, gemological labs are increasingly dependent on advanced technology for reliable gemstone identification.
The use of scientific instruments for gemstone identification makes it possible to decide on complex cases in a way that is repeatable and verifiable. The following is a summary of the high-tech instruments now in use in many of the world's leading gemological labs:
Fourier Transform Infrared Spectrometer (FTIR)
Infrared spectroscopy measures the absorption of infrared light. The absorption is due to vibrations in the crystal structure. This analysis can be used to help separate one gem material from another or to detect certain types of treatment. It can be used, for example, to identify synthetic and natural quartz, or identify polymer-impregnation of opal.
Energy Dispersive X-Ray Fluorescence Spectrometer (EDXRF)
The EDXRF system is used to analyse elements within a material. The radiation from an X-ray causes the atoms in the sample to release energy in the form of fluorescent radiation and the resulting X-ray can be analysed to determine the chemical elements in the gem. Coloring agents can be detected in many gem materials, as well as other elements that are evidence of certain treatment processes. For example, this is how copper is detected in Paraiba tourmaline.
Laser Induced Breakdown Spectrometer (LIBS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICP-MS)
These techniques involve shooting laser pulses that cut small particles from the surface of the sample material (a process known as laser ablation). These particles are ionized (converted into ions by removing electrons) into a small plume of plasma which grows. As the plasma grows, the atoms in the ionized gas emit spectral light, which is then analysed. The unique spectral signatures allow elements to be identified. This can be used for the rapid analysis of metals for the purpose of sorting and/or monitoring composition during processing. These methods can detect light elements such as beryllium that cannot be detected by FTIR or EDXRF. Very small quantities of trace elements that can help to identify the geographical origin of a gemstone can also be detected.
The Raman effect is a change in wavelength of light that occurs when it passes through a transparent medium. This results in a scattering of light in a pattern distinctive to the transmitting substance. Since each material has its own distinguishing spectral pattern, the Raman effect can be used as a tool of identification. Where LIBS and LA-ICP-MS are slightly destructive to the material being tested, Raman spectroscopy does not require destructive sampling.