The Post-Ilmenite Phases of Silicates, Germanates, and Titanates: A Review

The most significant findings in the recent high-pressure phase equilibrium studies relevant to the constitution of the deep mantle are believed to be the stable existence of MgSiO3 ilmenite [1,2] and MgSiO3 orthorhombic perovskite [2–5]. It also has been reported that the pyrope garnet transforms to the ilmenite structure which further converts to the orthorhombic perovskite at still higher pressures [6]. Therefore it is possible that the silicate perovskite is the major constituent in the lower mantle, and that the ilmenite phase is of importance in the lower-half of the transition zone.