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) Å, b = 4.947(2) Å, c = 6.950(3) Å, and V = 164.0(2) ų. 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 Al 2 O 3 in the lower mantle.