Metallic phases in the Luna 24 soil samples

The metal and sulfide phases in the Luna 24 soil samples were studied with the optical microscope and the electron microprobe. The compositions of the metal particles fall into three groups based on their Ni and Co contents: (1) Samples of meteoritic composition which have undergone metamorphism on the lunar surface. (2) Samples of submeteoritic, low Ni and low Co contents, including most of the metal particles observed. These particles are contained in glass and agglutinate particles and were probably formed by the mixing of meteoritic metal with lunar metal produced by the reduction of silicates during shock-impact. (3) Samples of high-CO content probably formed by mixing of meteoritic material with high-Co metal from the mare basalt or by fractional crystallization from a metal silicate melt. The sulfide minerals were also studied. These are almost pure FeS, and crystallized from a late stage liquid in the mare basalt. Three high-Ni sulfides were also found in the glass phase of agglutinates.