|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 increasingly depend on high technology for reliable gem identification.
The use of advanced scientific instrumentation for gemstone identification makes it possible to decide complex cases in a way which is repeatable and verifiable. Here 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 absorptions of a gem material in the infrared region of the electromagnetic spectrum. These absorptions are 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 treatments. 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 for the qualitative determination of a gemstones chemical composition. An X-ray beam illuminates the sample, and this energy causes the material to emit X-rays that are characteristic of the major and minor chemical elements in the gem. EDXRF is useful in detecting transition metal elements, which are the coloring agents 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 Couple Plasma Mass Spectrometer (LA-ICP-MS)
LIBS and LA-ICP-MS involve focussing a laser pulse onto a surface. The energy from the pulse heats, vaporizes, atomizes and then ionizes the material on the surface, resulting in a small, hot plasma. The atoms and ions in the plasma emit light which is then detected. The unique spectral signatures allow elements in the plasma to be identified. This technique can be applied to 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. They can also detect very small quantities of trace elements that can help to identify the geographical origin of a gemstone.
The Raman effect occurs when monochromatic light impinges upon a molecule and interacts with the electron cloud of the bonds of that molecule. The subsequent excitation 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.