2003 Volume 98 Issue 6 Pages 215-234
A single crystal high-pressure X-ray diffraction study of phase A was performed using a diamond anvil cell up to 11.2 GPa at ambient temperature. The chemical formula of this sample, determined by EPMA from an average of 18 data points, was Mg6.99Si1.99H6.06O14. Axial linear compressibilities of phase A were βa=2.92(2) and βc=2.17(3) (×10-3/GPa). The isothermal bulk modulus, calculated using the Birch-Murnaghan equation of state, was KT0=105(4) GPa with a pressure derivative K′=3.9(8) and V0=512.2(6) Å3. The bulk modulus correlates with the summation of the filling factor of the tetrahedral site and the octahedral site, as shown for the minerals on the forsterite-brucite join in the system MgO-SiO2-H2O.