Color Center in Amethyst Quartz

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Science  20 May 1966:
Vol. 152, Issue 3725, pp. 1061-1062
DOI: 10.1126/science.152.3725.1061


Treatment with x-rays increased the intensity of color of natural amethyst up to fivefold, and an electron paramagnetic resonance spectrum was detected. The intensity of the spectrum was proportional to the intensity of the optical absorption near 545 mµ. The EPR spectrum of the color center corresponded to a positive hole trapped on a substitutional Fe3+ ion in the quartz structure. We ascribe the color to a charge-transfer transition, Fe4+ + O2— → Fe3+ + O1-.