External reflectance infrared spectroscopy permits a very rapid and nondestructive determination of the species of a mineral. It is particularly useful with polished gems in that it requires no more than placing the stone, loose or mounted, on a reflection device in the infrared spectrometer and observing the recorded spectrum. Therefore, compared to the classical methods of physical measurement such as refractive index, specific gravity, and the like, reflectance spectroscopy provides a much faster means of establishing the species of the gem and, in some cases, whether it is natural or synthetic.
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