Synthesis of high-pressure phases of minerals*

Accurate sound velocity and elasticity data for Earth minerals measured at high pressure and temperature are essential for interpreting the Earth's interior's seismic velocity and density profiles in terms of the Earth's mineralogy and composition. We have fabricated optimum acoustic-quality synthetic polycrystalline wadsleyite (β-Mg₂SiO₄) specimens containing controlled water (OH) contents using hot-pressing techniques developed in a multi-anvil Kawai-type high-pressure apparatus. We have measured the acoustic velocity and elasticity in the samples at simultaneous high pressure and temperature using interferometry techniques in a multi-anvil device installed at the 6-BM-B beamline of the Advanced Photon Light Source Argonne National Laboratory. Integrating the beamline software automated controls and the multi-anvil interferometry systems enables fast measurements (less than 1s) of the travel times of acoustic waves in the sample and the sample density and length from synchrotron X-ray diffraction and X-radiography measurements, respectively. We examine the effects on the elasticity due to water incorporation in the wadsleyite and the impact of the hydrous mineral data on the Earth's mineralogical and chemical composition.