Nickel-cobalt systematics and their bearing on lunar origin

The earliest metal phases to crystallize from the least-fabricated low Ti mare basalts contain about 30% Ni and 2 to 7% of Co. Experimental investigations of partitioning of Ni and Co between primitive lunar basaltic magmas and metal phases are currently in progress. Preliminary results show that the metal phase crystallizing near the liquidus of Green Glass (185 ppm Ni, 70 ppm Co) would contain about 40% Ni and 2.3% Co. It seems, therefore, that if a lunar core does exist, as suggested by the results of (2), it is relatively rich in Ni (30-40%) and Co (2-7%). This composition presents a remarkable contrast to that of the Earth's core which is estimated to contain about 6% Ni and 0.3% Co. Explanations for the differing densities of Earth and Moon are imvestigated.