A new high-pressure phase transition in natural Fe-bearing orthoenstatite

Jin S. Zhang, Przemyslaw Dera, Jay D. Bass

Research output: Contribution to journalArticlepeer-review


Single-crystal X-ray structure refinements have been carried out on natural Fe-bearing orthoenstatite (OEN) at pressures up to 14.53 GPa. We report a new high-pressure phase transition from OEN to a monoclinic phase (HPCEN2) with space group P21/c, with a density change of ∼1.9(3)%. The HPCEN2 phase is crystallographically different from low-pressure clinoenstatite (LPCEN), which also has P21/c symmetry. Upon release of pressure HPCEN2 reverts to OEN, and the transition pressure is bracketed between 9.96 and 14.26 GPa at room temperature. We find no evidence for a C2/c phase at high pressure. The lattice constants for the new phase at 14.26 GPa are a = 17.87(2), b = 8.526(9), c = 4.9485(10) Å, β = 92.88(4)° [ρ = 3.658(9) g/cm3]. Refinement of the new structure indicates rotation of tetrahedral chain as the key characteristic of this transition. This experiment points to the possibility of OEN and HPCEN2 as the stable phases in Earth's upper mantle.

Original languageEnglish (US)
Pages (from-to)1070-1074
Number of pages5
JournalAmerican Mineralogist
Issue number7
StatePublished - Jul 2012


  • High-pressure clinoenstatite
  • High-pressure phase transition
  • Orthoenstatite
  • Synchrotron single-crystal X-ray diffraction
  • Upper mantle

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology


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