Amethyst: Optical Properties and Paramagnetic Resonance

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Science  17 Apr 1964:
Vol. 144, Issue 3616, pp. 289-290
DOI: 10.1126/science.144.3616.289


Color centers in amethyst are produced by the action of ionizing radiation on precursor centers that arise from substitution of Fe+3 for Si+4 in the α-quartz structure. These Fe+3 centers provide the dominant features of the electron paramagnetic resonance spectrum of amethyst. The three equivalent Si+4 sites are unequally occupied by Fe+3, a circumstance that explains the optical biaxiality of amethyst.