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Accurate determination of ferric iron in garnets

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Published/Copyright: July 7, 2016
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American Mineralogist
From the journal American Mineralogist Volume 101 Issue 7

Abstract

Numerous techniques are available to determine the amount of Fe2+ and Fe3+ in minerals. Calculating Fe2+ and Fe3+ by charge-balance using electron probe microanalysis (EPMA) data is the most common method, but several studies question the usefulness and accuracy of this approach (Canil and O’Neill 1996; Dyar et al. 1993, 2012; Lalonde et al. 1998; Li et al. 2005; McGuire et al. 1989; Schingaro et al. 2016; Schmid et al. 2003; Sobolev et al. 2011). We compile and compare data for natural garnets that have been analyzed by both EPMA and Mössbauer spectroscopy. Comparison of Fe3+/ΣFe determined by charge-balance vs. Mössbauer spectroscopy shows an approximate 1:1 correlation. The EPMA data set of Dyar et al. (2012) is reexamined and it is shown that disagreement between EPMA and Mössbauer for their data is not nearly as bad as reported. Data for charge-balance vs. Mössbauer spectroscopy are compared and show that the EPMA/charge-balance approach provides a suitable alternative when other methods are not practical.

Keywords: Ferric iron; EPMA; charge-balance; Mössbauer spectroscopy

Acknowledgments

The authors thank Mike Spicuzza, who first pointed out errors in Dyar et al. (2012); and helpful reviews from Keith Putirka and two anonymous reviewers. This research was supported by National Science Foundation grants EAR1524336 and EAR1144454.

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Received: 2016-1-27
Accepted: 2016-3-16
Published Online: 2016-7-7
Published in Print: 2016-7-1

© 2016 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am-2016-5695
Keywords for this article
Ferric iron; EPMA; charge-balance; Mössbauer spectroscopy

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  4. Alunite on Mars
  5. Special collection: martian rocks and minerals: perspectives from rovers, orbiters, and meteorites
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  7. Special collection: martian rocks and minerals: perspectives from rovers, orbiters, and meteorites
  8. Esperance: Multiple episodes of aqueous alteration involving fracture fills and coatings at Matijevic Hill, Mars
  9. Special collection: Martian rocks and minerals: perspectives from rovers, orbiters, and meteorites
  10. Discovery of alunite in cross crater, terra sirenum, mars: evidence for acidic, sulfurous waters
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