The generation and the removal of the various optical absorption bands in natural amethyst and in synthetic α-quartz doped with either Fe2+ or Fe3+ ions has been surveyed. Positive rhombohedral growth regions of synthetic α-quartz containing Fe3+ ion proved to be related to the generation of the amethyst color upon treatment with ionizing radiation. It is believed that the interstitial Fe8+ ions in voids perpendicular to positive rhombohedral faces furnish charge compensation for substitutional Fe3+ ion. This combination is the precursor of several color centers responsible for the production of the amethyst color.

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