Metastable phase transition of orthoenstatite (MgSiO3) under high pressure

Phase behavior of a synthetic orthoenstatite in a diamond-anvil cell has been studied up to ∼22GPa by using both in-situ X-ray diffraction and Raman spectroscopy. Under quasihydrostatic condition, it is found that orthoenstatite undergoes a reversible phase transition at room temperature. The hysteresis found in all four strong Raman modes suggests that the present metastable phase transition is of first order. The reversibility in the present phase transition reveals that orthoenstatite and clinoenstatite has different transition route and likely also different high-pressure polymorphs at room temperature.