The transition of orthoferrosilite to high-pressure C2/c clinoferrosilite at ambient temperature

Demelza Hugh-Jones, Thomas Sharp, Ross Angel, Alan Woodland

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41 Scopus citations


High-pressure single-crystal X-ray diffraction experiments on FeSiO3 orthoferrosilite have revealed that at pressures above ∼4.2GPa, the orthopyroxene transforms to a new phase. Examination by transmission electron microscopy of transformed material recovered from the diamond-anvil cell shows that the final product is predominantly low-clinoferrosilite (space group P21lc) with a few small islands of metastable C2lc clinoferrosilite. The presence of the C2/c clinoferrosilite, and the fact that this phase transforms readily to low-clinoferrosilite upon decompression below ∼1.5 GPa in hydrostatic conditions, confirms that the high-pressure clinoferrosilite was formed by the breakdown of orthoferrosilite at ∼4.2 GPa. The sequence of transformations is therefore: orthoferrosilite (Pbca) → (P increase above 4.2 GPa) → high-P clinoferrosilite (C2/c) → (P release below 1.5 GPa) → low-clinoferrosilite (P21lc) The transformation of orthoferrosilite to the high-pressure C2lc clinoferrosilite is highly time-dependent and first-order in character, accompanied by a ∼2.6% volume discontinuity. The morphology and microstructure of the recovered transformation products is indicative of a reconstructive transformation mechanism similar to that proposed previously for other orthopyroxene to clinopyroxene transformations.

Original languageEnglish (US)
Pages (from-to)1337-1345
Number of pages9
JournalEuropean Journal of Mineralogy
Issue number6
StatePublished - 1996
Externally publishedYes


  • FeSiO
  • Ferrosilite
  • High pressure
  • Phase transition

ASJC Scopus subject areas

  • Geochemistry and Petrology


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