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Physics and Chemistry of Minerals

, Volume 32, Issue 5–6, pp 388–399 | Cite as

Structure and physical property relations of Mn ilvaite

Part 1: Compositional, structural and Mössbauer data
  • K. T. FehrEmail author
  • J. Schneider
  • R. Hochleitner
  • E. Schmidbauer
Original Paper
  • 73 Downloads

Abstract

Structural and compositional data as well as 57Fe Mössbauer parameters were determined on a natural Mn-rich monoclinic ilvaite crystal (ideal composition CaFe 2 2+ Fe3+Si2O8(OH)) which was used for electrical conductivity and thermopower measurements (part 2 of this paper). A zonar structure was found by electron microprobe analysis with a strong decrease in Mn concentration from the rim to the centre of the crystal in a plane perpendicular to the [001] direction. X-ray powder diffraction analysis of the most Mn-rich composition was performed. Mn2+ cations populate preferentially M2 sites of the ilvaite unit cell (space group P21/a), to a lower extent they reside on M1 and a reduced part is on Ca sites. The monoclinic angle was determined to β=90.178(4)°. The structural results are compared to literature data for other natural Mn-rich as well as low-impurity ilvaites; this concerns in particular the lattice b parameter and the undecided issue of the varying β angle. In the literature, the order parameter σ, which describes the varying degree of ordering of Fe2+–Fe3+ pairs on M11 and M12 sites in chains running parallel to the [001] direction, and structural defects are thought to be related to β. The interrelationship between β and σ with respect to a possible twin domain structure is discussed. Various 57Fe Mössbauer spectra were recorded between 151 K and 327 K. Mössbauer parameters and Fe2+/Fe3+ concentration ratios were determined from the fits to the spectra. Fitting of subspectra was accomplished with the idea to find assignments of Fe2+ and Fe3+ doublets in agreement with X-ray results. The fraction of Mn2+ substituting Fe2+ on M1 sites could be estimated.

Keywords

X-ray diffraction Electron microprobe analysis 57Fe Mössbauer spectroscopy Mn-rich ilvaite 

Notes

Acknowledgements

One of the authors (E.S.) is indebted to the Deutsche Forschungsgemeinschaft for financial help.

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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • K. T. Fehr
    • 1
    Email author
  • J. Schneider
    • 2
  • R. Hochleitner
    • 3
  • E. Schmidbauer
    • 4
  1. 1.Department für Geo- und Umweltwissenschaften, Sektion Mineralogie, Petrologie und GeochemieUniversität MünchenMünchenGermany
  2. 2.Department für Geo- und Umweltwissenschaften, Sektion Kristallographie und MineralogieUniversität MünchenMünchenGermany
  3. 3.Mineralogische StaatssammlungMünchenGermany
  4. 4.Department für Geo- und Umweltwissenschaften, Sektion GeophysikUniversität MünchenMünchenGermany

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