BRILLOUIN-SCATTERING AND X-RAY-DIFFRACTION OF SAN-CARLOS OLIVINE - DIRECT PRESSURE DETERMINATION TO 32 GPA

The single-crystal elastic moduli of San Carlos olivine, (Mg0.9Fe0.1)( 2)SiO4, were determined at seven pressures between 2.5 and 32.5 GPa by Brillouin spectroscopy in a diamond anvil cell. The unit cell volume was also determined at each pressure (and ambient pressure) by single- crystal X-ray diffraction. The shear elastic moduli exhibit non-linear pressure dependencies, in particular, a non-linear dependence is requ ired for the elastic modulus, C-55, above 10 GPa. Aggregate bulk and s hear moduli were determined from Hashin-Shtrikman averages of the indi vidual constants. Pressures were determined by fitting the bulk modulu s (Reuss bound) and volume data to a third-order Eulerian finite strai n equation and integrating. The results are compared to independent pr essure measurements made using the ruby fluorescence scale. The ruby m easurements yield pressures that are in good agreement with the Brillo uin results. On average, the ruby fluorescence measurements produce pr essures that are larger than the Brillouin determinations by 1.6%. (C) 1998 Elsevier Science B.V. All rights reserved.