Magnetic properties of Apollo 12 lunar samples

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.