Another type of mare basalt, this moon rock is of a particular type called KREEP. Such rocks are rich in potassium (represented by K in the periodic table of elements), rare earth elements (REE) and phosphorous (P). As the magma ocean solidified, these KREEP components remained in the molten portion, becoming more concentrated. This heavier KREEP magma sank to the lower crust, where it solidified, until it was melted by rising basalt lava.
Keywords: Astrogeology, Astrophysics, Basalt, Lunar geology, Magmas, Meteorites, Phosphorus, Potassium, Rare earth metals