High-pressure synthesis of ZnSiO 3 ilmenite

Abstract

High-pressure phase relations in ZnSiO 3 and Zn 2SiO 4 were investigated at about 1000°C and in the pressure range of 100–500 kbar, using a double-staged split-sphere type of high-pressure apparatus. Clinopyroxene-type ZnSiO 3 transforms directly into a polymorph with the ilmenite structure at 120 kbar. The hexagonal unit cell dimensions of the ZnSiO 3 ilmenite are determined to be a = 4.746 ± 0.001 A ̊ and c = 13.755 ± 0.002 A ̊ under ambient conditions. The following reactions are also recognized at about 1000°C: ▪ and: ▪ The stabilities of silicate ilmenites, especially the absence of ilmenite of transition metal silicate composition, is discussed. It is pointed out that data on phase relations in zinc silicates may be informative for the consideration on those in magnesium silicates under very high pressures. It is suggested that the silicate ilmenite may be a major constituent in the lower mantle.