HIGH-PRESSURE TRANSFORMATION OF PYROPE (MG3AL2SI3O12) IN A SINTERED DIAMOND CUBIC ANVIL ASSEMBLY

Transformation of pyrope garnet was investigated at 1600 degrees 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) Angstrom, b = 4.947(2) Angstrom, c = 6.950(3) Angstrom and V = 164.0(2) Angstrom (3). A trace of stishovite observed in the run products may be evidenc e of nonstoichiometry in the perovskite. These results support the vie w that perovskite is the major host phase of Al2O3 in the lower mantle .