Stability of phase B, A hydrous magnesium silicate, to 2300°C at 20 GPA

The stability of phase B, hydrous magnesium silicate (Mg₂₃Si₈O₄₂H₆), has been investigated experimentally up to 20 GPa and 2500°C. Phase B is synthesized by heating a powder mixture of forsterite and periclase under hydrous conditions at pressures above 15 GPa, and temperatures above 1500°C, and is stable up to its incongruent melting temperature (2300°C at 20 GPa), above which it decomposes into an assemblage of liquid and periclase. The remarkable stability of phase B indicates the possibility of its presence as a host for H₂O in the deep upper mantle of the Earth.