In situ X-ray diffraction studies of hydrous aluminosilicate at high pressure and temperature

In situ X-ray diffraction studies of the phase relation of Al₂SiO₄(OH)₂ were conducted within a pressure range of 19.7-32.2 GPa and a temperature range of 800-1600 °C. We observed the coexistence of δ-AlOOH and stishovite at 31.0 GPa and 1500 °C and the formation of phase Egg together with corundum at 30.6 GPa and 1600 °C. Our results indicate that phase Egg is stable at least up to 31 GPa and 1600 °C and should be the important water carrier after the avalanche of the stagnant slab to a depth of approximately 900 km in the lower mantle.