Contributions to Mineralogy and Petrology

, Volume 166, Issue 2, pp 423–434 | Cite as

Quantification of the ferric/ferrous iron ratio in silicates by scanning transmission X-ray microscopy at the Fe L2,3 edges

  • Franck BourdelleEmail author
  • Karim Benzerara
  • Olivier Beyssac
  • Julie Cosmidis
  • Daniel R. Neuville
  • Gordon E. BrownJr.
  • Erwan Paineau
Original Paper


Estimation of Fe3+/ΣFe ratios in materials at the submicrometre scale has been a long-standing challenge in the Earth and environmental sciences because of the usefulness of this ratio in estimating redox conditions as well as for geothermometry. To date, few quantitative methods with submicrometric resolution have been developed for this purpose, and most of them have used electron energy-loss spectroscopy carried out in the ultra-high vacuum environment of a transmission electron microscope (TEM). Scanning transmission X-ray microscopy (STXM) is a relatively new technique complementary to TEM and is increasingly being used in the Earth sciences. Here, we detail an analytical procedure to quantify the Fe3+/ΣFe ratio in silicates using Fe L2,3-edge X-ray absorption near edge structure (XANES) spectra obtained by STXM, and we discuss its advantages and limitations. Two different methods for retrieving Fe3+/ΣFe ratios from XANES spectra are calibrated using reference samples with known Fe3+ content by independent approaches. The first method uses the intensity ratio of the two major peaks at the L3-edge. This method allows mapping of Fe3+/ΣFe ratios at a spatial scale better than 50 nm by the acquisition of 5 images only. The second method employs a 2-eV-wide integration window centred on the L2 maximum for Fe3+, which is compared to the total integral intensity of the Fe L2-edge. These two approaches are applied to metapelites from the Glarus massif (Switzerland), containing micrometre-sized chlorite and illite grains and prepared as ultrathin foils by focused ion beam milling. Nanometre-scale mapping of iron redox in these samples is presented and shows evidence of compositional zonation. The existence of such zonation has crucial implications for geothermometry and illustrates the importance of being able to measure Fe3+/ΣFe ratios at the submicrometre scale in geological samples.


Ferric/ferrous iron STXM XANES spectroscopy L2,3-edge Redox mapping Silicate 



We are most grateful to the Lawrence Berkeley National Lab and especially to Tolek Tyliszczak for his scientific support, and the Paul Scherrer Institute, Swiss Light Source. We would like to thank the materials characterisation department of IFP Energies nouvelles-Lyon and the laboratory of CP2M-Université Aix-Marseille, for technical advice. Thanks are also extended to Nicolas Menguy for his scientific help and to Christian Chopin (ENS, Paris), Daniel Beaufort (IC2MP, Poitiers), Patricia Patrier (IC2MP, Poitiers) and the Muséum National d’Histoire Naturelle. This study was supported by a grant from the Simone and Cino del Duca Foundation.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • Franck Bourdelle
    • 1
    • 2
    Email author
  • Karim Benzerara
    • 1
  • Olivier Beyssac
    • 1
  • Julie Cosmidis
    • 1
  • Daniel R. Neuville
    • 3
  • Gordon E. BrownJr.
    • 4
    • 5
  • Erwan Paineau
    • 6
    • 7
  1. 1.IMPMC, UPMC-CNRSParis cedex 05France
  2. 2.GeoRessources, Université de Lorraine, UMR 7359 CNRSVandœuvre-lés-NancyFrance
  3. 3.Géochimie et Cosmochimie, Institut de Physique du Globe de ParisUniversité Paris Diderot, Sorbonne Paris Cité, UMR 7154 CNRSParisFrance
  4. 4.Surface and Aqueous Geochemistry Group, Department of Geological and Environmental SciencesStanford UniversityStanfordUSA
  5. 5.SLAC Natl Accelerator LabStanford Synchrotron Radiation LightsourceMenlo PkUSA
  6. 6.Laboratoire de Physique des SolidesUniversité Paris-Sud, UMR 8502 CNRSOrsay cedexFrance
  7. 7.Laboratoire Interdisciplinaire sur l’Organisation Nanométrique et SupramoléculaireCEA Saclay, IRAMISGif-sur-Yvette cedexFrance

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