The post-spinel phase of forsterite

Abstract

THE nature of the post-spinel phase of forsterite (the olivine structure of Mg₂SiO₄) and its importance to our understanding of the mineralogy, petrology and seismological discontinuities in the transition zone and the lower mantle of the Earth has attracted much recent attention^1,2. Kumazawa et al.¹ reported that the post-spinel phase of forsterite recovered from 3.3 × 10¹⁰ Pa and 1,000 °C was a component oxide mixture of stishovite (SiO₂) plus periclase (MgO). In their studies of Mg₂SiO₄–Fe₂SiO₄ solid solutions at pressures up to 2.5 × 10¹⁰ Pa, Ming and Bassett² agreed with the conclusions of Kumazawa et al. Consequently, the oxide mixture seems to be widely accepted as the post-spinel phase of forsterite³. In this paper, however, I present results that disagree with this.