The complex impedance of a polycrystalline sample of San Carlo olivine including 5 vol% of a synthetic silicate glass containing sodium, magnesium, and iron has been measured as a function of temperature under controlled oxygen fugacity at a.c. frequencies of 102, 103, and 104 Hz. Below ~800 ¿C, the conductivity of the sample is at least 5 to 10 times higher than that of single crystal and polycrystalline San Carlos olivine, respectively, and has an activation energy half that of the single crystal. The sample conductivity increases dramatically as a function of the measurement frequency. Hysteresis and time-dependent changes in sample conductivity are observed above the liquidus of the glass (~900 ¿C). The data suggest that the electrical conductivity of partially molten samples is characterized by parallel conduction of the solid and melt phases and is a sensitive indicator of melt distribution as well as the kinetics of melt re-equilibration. ¿ American Geophysical Union 1993