A new high-pressure phase transition in clinoferrosilite; in situ single-crystal X-ray diffraction study

Synchrotron-based high-pressure single-crystal X-ray diffraction experiments were conducted on synthetic pure clinoferrosilite, Fe (sub 2) Si (sub 2) O (sub 6) , at room temperature to a maximum pressure of 45 GPa. In addition to the previously described P2 (sub 1) /c --> C2/c phase transition between 1.48 and 1.75 GPa (Hugh-Jones et al. 1994), we observe further transition between 30 and 36 GPa into the high-pressure P2 (sub 1) /c phase (HP-P2 (sub 1) /c). The C2/c --> HP-P2 (sub 1) /c transition is induced by rearrangement of half of the layers of corner-sharing SiO (sub 4) tetrahedra into layers of edge-sharing SiO (sub 6) octahedra. The new configuration of (super VI) Si layers suggests a possibility of a progressive transformation of the pyroxene into an ilmenite-type structure. The persistence of metastable pyroxene up to pressures higher than expected and its feasible direct transformation to ilmenite are of special interest for understanding the dynamics of cold-subducting slabs. We report on structural and compressibility features of both high-pressure phases as well as address thermal stability of HP-P2 (sub 1) /c.