Compressional velocities of polycrystalline olivine, spinel and rutile minerals

Abstract

Polycrystalline aggregates of the following minerals have been hot-pressed in a piston-cylinder apparatus (P≤35 kbar, T≤1200°C): olivines - Mg 2SiO 4, Mg 2GeO 4, Ni 2SiO 4; spinels - Mg 2GeO 4, Fe 2GeO 4, Co 2GeO 4, Ni 2GeO 4; rutiles - TiO 2, GeO 2, SnO 2. These specimens are less than 3% porous and less than 100 micron grain size. Compressional velocities are determined as a function of pressure to 7.5 kbar at room temperature by the ultrasonic pulse transmission method. Comparison with published data for single crystal Mg 2SiO 4, TiO 2 and GeO 2 indicates that the present specimens are elastically isotropic within the precision of the current measurements (±2%). The velocity jump at the olivine-spinel transition in Mg 2GeO 4 is 16%, whereas the density jump is 8%. Data for Mg 2GeO 4 olivine and spinel and Fe 2GeO 4 spinel suggest that data for germanate compounds may be used to estimate the elastic properties of their silicate analogs.