High temperature X-ray diffraction study of enstatite up to the melting point

Abstract

In order to examine the phase relations of enstatite at high temperatures, high temperature X-ray powder diffraction experiments were performed with low clinoenstatite MgSiO3 as starting materials. It was observed that upon heating low clinoenstatite transformed into protoenstatite at around 1100°C and protoenstatite persisted up to the melting point, indicating that protoenstatite is the high temperature stable phase for MgSiO3 up to the melting point. Two extra peaks (d=3.074-3.079 Å and 3.323-3.331 Å at 1200°C) which could not be indexed as low clinoenstatite or protoenstatite, appeared along with protoenstatite at around 1150°C, but they disappeared at temperatures above ∼ 1400°C. These extra peaks did not reappear on cooling of protoenstatite. This indicates that these extra peaks originate from high temperature clinoenstatite metastably transformed from low clinoenstatite and that high temperature clinoenstatite has no stability field above and below that of protoenstatite.