The influence of oxidation state on the electrical conductivity of olivine

The electrical conductivity of a single crystal of San Carlos olivine (Fo₉₂, 0.16 wt.% Fe₂O₃) has been measured as a function of temperature and oxygen fugacity (fO₂). After heating to 1338°C at fO₂ = 10^?12 atm., the conductivity at 950°C was 10^?5 (ohm-m)^?1, almost 3 orders of magnitude less than that measured in air. This decrease is due to the reduction of Fe³⁺ to Fe²⁺. Further heating to 1500°C at fO₂ = 10^?14 atm., decreased the electrical conductivity at 950°C to 10^?6 (ohm-m)^?1. When recovered at room temperature, the speciment had Fo₉₆ composition and contained small, opaque blebs distributed throughout the crystal. Derivations of temperature profiles for the earth's mantle from conductivity-depth models must take account of the important role played by iron oxidation state in the electrical conductivity of olivine.