For certain crystal orientations and diffraction conditions, electron-induced characteristic X-ray emission produces anomalous intensities as a result of electron channeling. These intensities can be used to determine directly the chemical compositions of specific crystallographic sites within individual crystals. We have used this channeling method to determine the Al-Si ordering in gem orthoclase from Ampandrandava, Madagascar. We find that 71 atomic percent of the Al occupies the T1 site, in agreement with the values derived from standard X-ray powder diffraction data.
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