Elastic properties of polycrystalline SnO2 and GeO2: comparison with stishovite and rutile data

Polycrystalline aggregates of SnO2-cassiterite and GeO2-rutile have been hot-pressed in a piston-cylinder apparatus at P = 30 kbar and T ⩽ 1,000°C. These specimens are less than 2% porous and less than 20μ in grain size. Compressional (Vp) and shear (Vs) velocities are determined as a function of pressure to 7.5 kbar at 293 K by the ultrasonic-pulse superposition method. Extrapolation of the velocity—pressure data to P = 1 ba yields the following velocities (units: km/sec) for the compressed polycrystalline aggregate SnO2: Vp = 6.91, Vs = 3.75; for GeO2: Vp = 8.56, Vs = 4.83. Comparison with published data for single-crystal GeO2 indicates that our specimen is elastically isotrop within 1%. The bulk sound velocities (Vφ) for the rutile minerals SiO2, GeO2 and SnO2 are systematically related to density, with TiO2 being anomalous. Shankland's (1972) equation (∂ ln Vφ∂ ln M)x = − 12 (where M is mean atomic weight) represents these rutile data well.