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

Using single-crystal XRD, it has been shown that orthoferrosilite transforms to the high-P C2/c pyroxene polymorph of FeSiO (sub 3) at P >><$I> 4.6 GPa at room T under hydrostatic conditions. Experiments on two samples show that this transformation is highly time-dependent, and must be reconstructive, involving significant shearing and breaking of bonds. The highly strained microstructures in the C2/c and P2 (sub 1) /c product phases are consistent with such a reconstructive Pbca ->> C2/c transition at room T. The persistence of small amounts of the C2/c structure, previously considered non-quenchable, indicates that the relatively easy transformation of C2/c to P2 (sub 1) /c structures can be inhibited by defects in high-P clinoferrosilite caused by the transformation from orthoferrosilite.