QUANTITATIVE-DETERMINATION OF THE OXIDATION-STATE OF IRON IN BIOTITE USING X-RAY PHOTOELECTRON-SPECTROSCOPY - II - IN-SITU ANALYSES

X-ray photoelectron spectroscopy (XPS) was used to determine Fe(III)/S igma Fe in individual biotite crystals in thin sections of ten metapel ites and one syenite. The in situ XPS analyses of Fe(III)/Sigma Fe in biotite crystals in the metapelites were compared with published Fe(II I)/Sigma Fe values determined by Mossbauer spectroscopy (MS) for miner al separates from the same hand samples. The difference between Fe(III )/Sigma Fe by the two techniques was greatest for samples with the low est Fe(III)/Sigma Fe (by MS). For eight metamorphic biotites with Fe(I II)/Sigma Fe = 9-27% comparison of the two techniques yielded a linear correlation of r = 0.94 and a statistically acceptable fit of [Fe(III )/Sigma Fe](xps) = [Fe(III)/Sigma Fe](ms). The difference between Fe(I II)/Sigma Fe by the two techniques was greater for two samples with Fe (III)/Sigma Fe less than or equal to 6% (by MS). For biotite in the sy enite sample, Fe(III)/Sigma Fe determined by both in situ XPS and bulk wet chemistry/electron probe microanalysis were similar. This contrib ution demonstrates that XPS can be used to analyze bulk Fe(III)/Sigma Fe in minerals in thin sections when appropriate precautions are taken to avoid oxidation of the near-surface during preparation of samples. Copyright (C) 1997 Elsevier Science Ltd.