Electrical conductivity of pyroxene which contains trivalent cations: Laboratory measurements and the lunar temperature profile

Three natural orthopyroxene single crystals, measured in the laboratory over the temperature range 850°–1200°C, are more than ½ order of magnitude more electrically conducting than previously measured crystals. Small concentrations (1–2%) of Al 2 O 3 and Cr 2 O 3 present in these crystals may be responsible for their relatively high conductivity. Such pyroxenes, which contain trivalent elements, are more representative of pyroxenes expected to be present in the lunar mantle than those which have been measured by other investigators. The new conductivity values for pyroxene are responsible for a relatively large bulk conductivity calculated for (polymineralic) lunar mantle assemblages. The results permit a somewhat cooler lunar temperature profile than previously proposed. Such lower profiles, several hundred degrees Celsius below the solidus, are quite consistent with low seismic attenuation and deep moonquakes observed in the lunar mantle.