Home The order-disorder character of FeOHSO4 obtained from the thermal decomposition of metahohmannite, Fe3+2(H2O)4[O(SO4)2]
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The order-disorder character of FeOHSO4 obtained from the thermal decomposition of metahohmannite, Fe3+2(H2O)4[O(SO4)2]

  • Gennaro Ventruti , Fernando Scordari EMAIL logo , Emanuela Schingaro , Alessandro F. Gualtieri and Carlo Meneghini
Published/Copyright: March 28, 2015
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American Mineralogist
From the journal American Mineralogist Volume 90 Issue 4

Abstract

The iron sulfate FeOHSO4 studied was obtained as a dehydration product of metahohmannite Fe2(H2O)4[O(SO4)2] during a synchrotron real-time powder diffraction experiment. As quoted in the literature, FeOHSO4 has iron atoms octahedrally coordinated with two hydroxyl groups and four sulfate O atoms, while each hydroxyl group is bonded to two iron atoms. This compound is commonly described in the orthorhombic system with space group Pnma, lattice parameters aJ = 7.33, bJ = 6.42, and cJ = 7.14 Å (aJ, bJ, and cJ are the Johansson lattice parameters), and Z = 4. However a preliminary Rietveld refinement of the pattern at about 220 °C using the structural model from the literature yielded a poor fit of the observed data and a final Rp value of about 23%. A careful analysis of the calculated powder diffraction pattern showed unexpected peaks, not observed in the experimental trace, for h = 2n + 1, while sharp reflections for h = 2n seemed to point to different lattice constants and space group. The recognition of the order-disorder character of the FeOHSO4 compound was the key to successfully interpreting the unexpected features of the experimental powder pattern and the misfit with respect to the calculated pattern. In fact, FeOHSO4 belongs to a family of OD structures formed by equivalent layers of symmetry Pbmm. Only two MDO (Maximum Degree of Order) polytypes are possible. MDO1 results from a regular alternation of stacking operators 21/2 and 2-1/2, and yields an orthorhombic structure with space group Pnma and lattice parameters aJ = 7.33, bJ = 6.42, and cJ = 7.14 Å. MDO2 results from the 21/2|21/2 |21/2... sequence of symmetry operators and yields a monoclinic structure with space group P21/c, aM = 7.33, bM = 7.14, cM = 7.39 Å, and β = 119.7°.

The analysis of one-dimensional stacking disorder was performed by fitting the observed XRPD pattern with a calculated intensity curve generated by DIFFaX. The disorder model was investigated by taking into account a probability matrix for the occurrence of OD layer sequences. The best fit (Rp = 0.009) to the observed powder pattern was obtained with a 61:39 ratio of monoclinic and orthorhombic polytypes for a fully disordered OD layers sequence.

Received: 2004-6-4
Accepted: 2004-7-23
Published Online: 2015-3-28
Published in Print: 2005-4-1

© 2015 by Walter de Gruyter Berlin/Boston

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  13. Direct formation of the γ-CaSO4 phase in dehydration process of gypsum: In situ FTIR study
  14. The order-disorder character of FeOHSO4 obtained from the thermal decomposition of metahohmannite, Fe3+2(H2O)4[O(SO4)2]
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  24. Letter. Differentiation of commercial vermiculite based on statistical analysis of bulk chemical data: Fingerprinting vermiculite from Libby, Montana U.S.A.
  25. Letter. Crystal structure of single-crystal CaGeO3 tetragonal garnet synthesized at 3 GPa and 1000 °C
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https://doi.org/10.2138/am.2005.1739

Articles in the same Issue

  1. Analytical perils (and progress) in electron microprobe trace element analysis applied to geochronology: Background acquisition, interferences, and beam irradiation effects
  2. Contributions to precision and accuracy of monazite microprobe ages
  3. Electron-microprobe age mapping of monazite
  4. Isotopic age constraints from electron microprobe U-Th-Pb dates, using a three-dimensional concordia diagram
  5. Monazite ages in the Chesham Pond Nappe, SW New Hampshire, U.S.A.: Implications for assembly of central New England thrust sheets
  6. Electron-microprobe dating as a tool for determining the closure of Th-U-Pb systems in migmatitic monazites
  7. Comparative isotopic and chemical geochronometry of monazite, with implications for U-Th-Pb dating by electron microprobe: An example from metamorphic rocks of the eastern Wyoming Craton (U.S.A.)
  8. Re-examination of the hydrogarnet structure at high pressure using neutron powder diffraction and infrared spectroscopy
  9. Anomalous elastic behavior and high-pressure structural evolution of zeolite levyne
  10. Crystal chemistry of the hydrothermally synthesized Na2(Mn1-xFex 2+)2Fe3+(PO4)3 alluaudite-type solid solution
  11. Thermodynamic properties of uvarovite garnet (Ca3Cr2Si3O12)
  12. Post-aragonite phase transformation in CaCO3 at 40 GPa
  13. Direct formation of the γ-CaSO4 phase in dehydration process of gypsum: In situ FTIR study
  14. The order-disorder character of FeOHSO4 obtained from the thermal decomposition of metahohmannite, Fe3+2(H2O)4[O(SO4)2]
  15. Temperature and composition dependence of structural phase transitions in Ca(TixZr1-x)OGeO4
  16. Low-T neutron powder-diffraction and synchrotron-radiation IR study of synthetic amphibole Na(NaMg)Mg5Si8O22(OH)2
  17. Charge contrast imaging of fine-scale microstructure and compositional variation in garnet using the environmental scanning electron microscope
  18. Piston-cylinder experiments on H2O undersaturated Fe-bearing systems: An experimental setup approaching fO₂ conditions of natural calc-alkaline magmas
  19. Environmentally important, poorly crystalline Fe/Mn hydrous oxides: Ferrihydrite and a possibly new vernadite-like mineral from the Clark Fork River Superfund Complex
  20. The true structure of wonesite, an interlayer-deficient trioctahedral sodium mica
  21. Clinoholmquistite discredited: The new amphibole end-member fluoro-sodic-pedrizite
  22. XRMapAnal: A program for analysis of quantitative X-ray maps
  23. Letter. Growth zoning and strain patterns inside diamond crystals as revealed by Raman maps
  24. Letter. Differentiation of commercial vermiculite based on statistical analysis of bulk chemical data: Fingerprinting vermiculite from Libby, Montana U.S.A.
  25. Letter. Crystal structure of single-crystal CaGeO3 tetragonal garnet synthesized at 3 GPa and 1000 °C
  26. Letter. Iron isotope exchange kinetics at the nanoparticulate ferrihydrite surface
  27. Letter. Cation distribution in MgFe2O4 vs. pressure and temperature: Experiments in a piston-cylinder apparatus
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