High-pressure transformation of pyrope (Mg3Al2Si3O12) in a sintered diamond cubic anvil assembly

Abstract

Transformation of pyrope garnet was investigated at 1600 °C and at pressures higher than 35 GPa using a sintered diamond cubic anvil assembly in a double-staged split-sphere apparatus. Pyrope transformed into orthorhombic perovskite at ca. 37 GPa, whereas a small amount of corundum coexisted with perovskite at lower pressures. The unit cell dimensions of perovskite were determined to be a = 4.771(2) angstroms, b EQ 4.947(2) angstroms, c = 6.950(3) angstroms, and V = 164.0(2) angstroms3. A trace of stishovite observed in the run products may be evidence of nonstoichiometry in the perovskite. These results support the view that perovskite is the major host phase of Al2O3 in the lower mantle.