Unstable, green, irradiation-induced color in grossularite
Kurt Nassau
Lebanon, New Jersey
George R. Rossman
California Institute of Technology, Pasadena, California
Darwin L. Wood
Murray Hill, New Jersey
Abstract
Although conventional wisdon has been that irradiatoin will not alter
the color of garnets, exposure of some colorless to pale-hued Africian
grossulars to either 60Co or 137Cs gamma rays turns them light
yellow-green. The resulting color is unstable and fades within hours to
days in sunlight, and within weeks in the dark. The spectra of the
radiation-enhanced garnets differ from those of similiar-appearing
naturally colored grossulars. In the dark, the irradiation-related
absorption features undergo two stages of fading: an initial period of
relatively rapid fading, followed by a longer period of slow fading. In
daylight, a single rate of even faster fading is observed.