The relationship between lunar metal particles and phosphate minerals

Phosphorus is often present in lunar rocks and soils in bulk concentrations in excess of 0.5 wt % P205. The minerals apatite and whitlockite account for most of the phosphorus. However, it may also be present in metal grains. The relations between metal particles and the phosphates commonly found adjacent to these particles are investigated, taking into account studies involving three Apollo 17 rocks. It appears that phosphorus in lunar metal particles is related to the phosphate minerals by a redox reaction. The independent phosphates probably formed over much of the cooling period of the rock. While the rock was at high temperature, however, phosphorus was free to diffuse and dissolve in the metal droplets providing conditions were sufficiently reducing. If the rock was partially molten, this process would take less than 1 hr. If cooling occurred slowly under less reducing conditions, some of the phosphorus in the metal particles would be oxidized to form whitlockite.