PHASE-F, A NEW HYDROUS MAGNESIUM-SILICATE SYNTHESIZED AT 1000-DEGREES-C AND 17 GPA - CRYSTAL-STRUCTURE AND ESTIMATED BULK MODULUS

The structure of phase F, a non-stoichiometric hydrous silicate synthe sized in a uniaxial, split-sphere, multi-anvil apparatus at conditions of 17 GPa and 1000 degrees C, has been solved and refined in space gr oup P6(3)cm, using synchrotron X-ray data for a single crystal of a si ze 18 x 24 x 30 mu m. The composition and unit cell for phase F are Mg 3.35Si5.51H7.26O18, a = 5.073(3) Angstrom c = 14.013(9) Angstrom, V = 312.3(5) Angstrom(3). The structure contains layers with many similari ties to superhydrous phase B. The layers of oxygen atoms are stacked i n the ABCBAC-type double cubic closest packing arrangement. The bulk m odulus of phase F was estimated from the structural and compositional relationship to superhydrous phase B and periclase.