Magnetic properties of Apollo 12 lunar samples

Abstract

The magnetic properties of crystalline rock and fines returned by the Apollo 12 mission have been measured. The fines contain at least 0.7% by mass of native iron, mainly in the super- paramagnetic form at room temperature. Native iron is present in the crystalline rock but in a much lower concentration. The paramagnetic minerals, ilmenite and ulvöspinel, are present. Some evidence has been obtained that magnetite is present in the crystalline rock, less than 0.02% by mass. It has not yet been established whether it is indigenous to the rock. Two samples exhibit a change in n.r.m. at low temperature consistent with this n.r.m. being carried by magnetite, but these investigations are not yet complete. The crystalline rocks possess an n.r.m. of intermediate stability: there is evidence for two components of magnetization, a weak and rather stable one, and a less stable but stronger component. The former indicates the presence of a magnetic field on the moon at the time of formation of the rocks. An external origin seems unlikely: thus the Moon possessed a magnetic field of internal origin 3400 Ma§ ago which has since decayed.