title: Amethyst: Optical Properties and Paramagnetic Resonance.
abstract: 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 alpha-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.
authors.forename: T I
authors.initials: TI
authors.lastname: Barry
authors.forename: W J
authors.initials: WJ
authors.lastname: Moore