A comparison of the effects of pressure, temperature, and H2O adsorption and desorption on the electrical conductivity of basalts

At 16°C and 10−7 torr the conductivity of basalt is of the order of 10−14 (Ωcm)−1. Raising the H2O vapor pressure from zero to saturation increases the conductivity to 10−6 (Ω cm)−1. A change in conductivity of the same order of magnitude can be accomplished by heating a dry sample at 10−7 torr to 450°C-500°C. Quasi-hydrostatic pressure of 50 kbar increases the conductivity of dry basalt at most by 1 ½ orders of magnitude and more typically by a factor of 3.5. Prolonged heating increases the conductivity of dry basalt and alters its variations in response to changes in H2O vapor pressure. Activitation energies in the higher temperature region up to the melting point are of the order of 1.1 eV. Beyond the high-pressure melting point the conductivity is found to increase to 2×10−1 (Ω cm)−1 following premonitory decreases.