Anisotropy of electrical conductivity in dry olivine

Abstract

The electrical conductivity (σ) was measured for a single crystal of San Carlos olivine (Fo89.1) for all three principal orientations over oxygen fugacities 10-7 < fO2 < 101 Pa at 1100, 1200, and 1300°C. Fe-doped Pt electrodes were used in conjunction with a conservative range of fO2, T, and time to reduce Fe loss resulting in data that is ∼0.15 log units higher in conductivity than previous studies. At 1200°C and fO2) = 10-1 Pa, σ[100] = 10-2.27S/m, σ[010] = 10-2.49S/m, σ[001] = 10-2.40S/m. The dependences of σ on T and fO2 have been simultaneously modeled with undifferentiated mixed conduction of small polarons and Mg vacancies to obtain steady-state fO2-independent activation energies: Ea[100] = 0.32 eV, Ea[010] = 0.56 eV, Ea[100] = 0.71 eV. A single crystal of dry olivine would provide a maximum of ∼100.4 S/m azimuthal σ contrast for T < 1500°C. The anisotropic results are combined to create an isotropic model with Ea = 0.53 eV. Copyright 2005 by the American Geophysical Union.