Smoky, blue, greenish yellow, and other irradiation-related colors in quartz

SUMMARY. Almost 4oo specimens of natural and synthetic quartz were ~,-irradiated and then heated. Polarized absorption spectroscopy, EPR, and spectrochemical analysis were used to investigate the various colors pro-duced. A blue color originated from absorption by the At and A ~ bands at 1"85 and 2'55 eV. The substitutional A1 EPR hole-type center usually considered to be the cause of the color in smoky quartz does not correlate with A t and Az, but with Aa, a previously unreported absorption band at 2'9o eV. The At and A ~ absorptions bleach at temperatures a low as 28o ~ and as high as 36o ~ the range for Aa being 14o to 38o ~ The B band at 3"95 eV was previously reported only in irradiated fused silica. Greenish-yellow colors (appearing yellow when of low intensity) were observed after irradiation (followed by heating in some instances) in many specimens of natural and synthetic quartz; the color originates from the tail of a strong absorption band in the ultraviolet. The bleaching temperature ange is the same as that for As. The wide variation in color of natural and irradiated smoky quartz can be explained by combinations of the smoky (As), blue (A t and Az), and greenish yellow absorption features. THREE colors have been attributed to the effect of irradiation, such as X-rays or 7-rays, on quartz: smoky, amethyst, and greenish yellow