Synchrotron XRF microprobe analysis of geological samples: Influence of size and orientation of single mineral grains

The results of a photon microprobe study on the influence of size and orien tation of single mineral grains on geochemical data when analysing geologic al samples are presented. A large crystal of primary pegmatitic muscovite a nd an aggregate of small lamellar secondary lepidolite grains were analysed at various points. The primary synchrotron radiation beam orientation has a negligible effect upon geochemical data for tetrahedral and octahedral ca tions in both minerals. Conversely, the analytical results for the large in terlayer cations are significantly more dispersed when the incident beam is parallel to the (001) plane of the crystal(s), Furthermore, the analysis o f the sub-parallel aggregate of lepidolite minute crystals provided higher concentration figures for substituting large cations (particularly caesium) when the incoming beam was so oriented. Copyright (C) 1999 John Wiley & So ns, Ltd.