Since the first synthetic amethyst was commercially manufactured about 30 years ago, the separation from natural material has been difficult for gemologists. Even today, the separation of natural from hydrothermally grown in K2C03 synthetic amethyst is still an issue. With only the help of classical gemological criteria (such as inclusions, twinning and color zoning) it is difficult to separate synthetic stones from their natural counterparts. The separation problem is even more complex in the

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... ase of the highest quality (and value) of amethysts presenting neither inclusion nor twinning nor color zoning. IR absorption spectra of amethyst in the region of the ΧΟΗ group stretching (particularly from 3000 to 3900 cm'1) reveal several bands that have been used for the separation of natural from synthetic amethyst. Using a resolution at 0.5 cm the 3595 cm1 band is present in all natural amethyst and in some rare synthetic ones. When present in synthetic amethysts, its full width at half maximum (FWHM) is about 7 cm , whereas it is about 3.3 cm' in all naturals. This new criterion worked for all of our samples.