Possible Sites for Hydrogen in a New Hydrous Magnesium Silicate Phase G Synthesized at 22 GPa and 1050°C

A single crystal ofphase G, Mg1. 24Si1. 76H2. 48O6was analized with synchrotron radiation. The structure ofphase G has close structural similarity to that ofstishovite, SiO2. The valence sum ofthe O site is 1. 52, indicating the existenceofhydrogen bonding as anion chemistry for oxygen being OH1/2. The possible sites for hydrogen are along the O-O edge of vacant tetrahedrabetween corners of MgO6 octahedrawhich are separated by a distance of 2. 654 (6) A.