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Analyzing Mg and Fe in Olivines, Pyroxenes, and Garnets: Systematic Discrepancies

Published online by Cambridge University Press:  02 July 2020

P. Carpenter  and
J. Armstrong
P. Carpenter
Affiliation:
Analytical Facility, Division of Earth and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125
J. Armstrong
Affiliation:
Surface and Microanalysis Science Division, National Institute of Standards and Technology, Gaithersburg, MD, 20899
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Extract

Quantitative analysis of Mg and Fe in olivines, pyroxenes, and garnets is important for geochemical studies. Natural olivines have compositions close to the forsterite (Mg2SiO4) and fayalite (Fe2SiO4) binary system, with relatively minor substitution of other components. Pyroxenes and garnets are problematic in that they exhibit more diverse solid solution, and may contain both Fe2+ and Fe3+, the relative concentrations of which cannot be directly measured with the microprobe. The forsterite-fayalite olivine binary is a convenient system for studying the accuracy of Mg and Fe analysis without other complicating factors.

Bence and Albee utilized the a-factor approach for quantitative analysis of silicates, based on the empirical observation:

where CA,AB is the weight fraction of the oxide A in a binary oxide system AB, and KA,AB is the measured x-ray intensity of A relative to that of the pure oxide A.

Type
Problem Elements and Spectrometry Problems in X-Ray Microanalysis
Information
Microscopy and Microanalysis , Volume 4 , Issue S2: Proceedings: Microscopy & Microanalysis '98, Microscopy Society of America 56th Annual Meeting, Microbeam Analysis Society 32nd Annual Meeting, Atlanta, Georgia July 12-16, 1998 , July 1998 , pp. 224 - 225
Copyright
Copyright © Microscopy Society of America

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References

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