Effect of conductive impurities on electrical conductivity in polycrystalline olivine

Bulk electrical conductivity and impedance spectroscopy of single crystal and polycrystalline San Carlos olivine with carbon or iron sulfide impurities on grain boundaries were measured at 1GPa and 350 degrees C-1200 degrees C in a piston cylinder apparatus. The addition of 0.1 wt% (similar to 0.16 vol%) C causes series-type grain boundary impedance in the samples that slightly decreases the bulk conductivity of the system. In contrast, the addition of 1.0 vol% sulfide results in conductivity much higher than plain olivine, but still lower than that of a fully interconnected sulfide phase. The sulfide is partially connected on the grain boundaries and edges and has reached the electrical percolation threshold. The effect adding sulfide is similar to the effect of adding 0.01%-0.1% H to olivine. It may not always be necessary to have hydrogen or connected melt or fluid to account for anomalously high conductivity in some parts of the mantle or crust. Citation: Watson, H. C., J. J. Roberts, and J. A. Tyburczy (2010), Effect of conductive impurities on electrical conductivity in polycrystalline olivine, Geophys. Res. Lett., 37, L02302, doi:10.1029/2009GL041566.