Electronic transitions of iron in almandine-composition glass to 91 GPa

Susannah M. Dorfman, Sian E. Dutton, Vasily Potapkin, Aleksandr I. Chumakov, Jean Pascal Rueff, Paul Chow, Yuming Xiao, Robert J. Cava, Thomas S. Duffy, Catherine A. McCammon, Philippe Gillet

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Valence and spin states of Fe were investigated in a glass of almandine (Fe3Al2Si3O12) composition to 91 GPa by X-ray emission spectroscopy and energy-and time-domain synchrotron Mossbauer spectroscopy in the diamond-anvil cell. Changes in optical properties, total spin moment and Mossbauer parameters all occur predominantly between 1 bar and ~30 GPa. Over this pressure range, the glass changes from translucent brown to opaque and black. The total spin moment of the glass derived from X ray emission spectroscopy decreases by ~20%. The complementary Mossbauer spectroscopy approaches reveal consistent changes in sites corresponding to 80-90% Fe2+ and 10-20% Fe3+. The high-spin Fe2+ doublet exhibits a continuous decrease in isomer shift and increase in line width and asymmetry. A high-spin Fe3+ doublet with quadrupole splitting of ~1.2 mm/s is replaced by a doublet with quadrupole splitting of ~1.9 mm/s, a value higher than all previous measurements of high-spin Fe3+ and consistent with low-spin Fe3+. These observations suggest that Fe3+ in the glass undergoes a continual transition from a high-spin to a low-spin state between 1 bar and ~30 GPa. Almandine glass is not expected to undergo any abrupt transitions in electronic state at deep mantle pressures.

Original languageEnglish (US)
Pages (from-to)1659-1667
Number of pages9
JournalAmerican Mineralogist
Issue number7
StatePublished - Jul 1 2016

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology


  • Mossbauer spectroscopy
  • Silicate glass
  • X ray emission spectroscopy
  • nuclear forward scattering
  • spin transitions


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