A Transmission Electron Microscope Study of Amethyst and Citrine

Abstract

Thin crystals of amethyst and citrine were examined by transmission elflf'troJl microscopy. It was found that all crystals became damaged during observflti"ll. The diffraction contrast from the damage centres indicated that these were RmfLll amorphous regions. Electron spin resonance observations of these crystals show that the amorphous regions are associated with Fe3+ ions; the damage centres provide, therefore, a measure of the distribution of this impurity in the crystals. Brazil twin boundaries, generally of the order of 1000 A apart, were observed directly. Radiation damage occurred preferentially at the twin boundaries suggesting that there was a concentration of impurities along them. The relevance of these observations to the optical properties of the crystals is discussed briefly.