<P> Composite rocks on the lunar surface often appear in the form of breccias . Of these, the subcategories are called fragmental, granulitic, and impact - melt breccias, depending on how they were formed . The mafic impact melt breccias, which are typified by the low - K Fra Mauro composition, have a higher proportion of iron and magnesium than typical upper crust anorthositic rocks, as well as higher abundances of KREEP . </P> <P> The main characteristics of the basaltic rocks with respect to the rocks of the lunar highlands is that the basalts contain higher abundances of olivine and pyroxene, and less plagioclase . They are more rich in iron than terrestrial basalts, and also have lower viscosities . Some of them have high abundances of a ferro - titanic oxide called ilmenite . Because the first sampling of rocks contained a high content of ilmenite and other related minerals, they received the name of "high titanium" basalts . The Apollo 12 mission returned to Earth with basalts of lower titanium concentrations, and these were dubbed "low titanium" basalts . Subsequent missions, including the Soviet robotic probes, returned with basalts with even lower concentrations, now called "very low titanium" basalts . The Clementine space probe returned data showing that the mare basalts have a continuum in titanium concentrations, with the highest concentration rocks being the least abundant . </P> <P> The current model of the interior of the Moon was derived using seismometers left behind during the crewed Apollo program missions, as well as investigations of the Moon's gravity field and rotation . </P> <P> The mass of the Moon is sufficient to eliminate any voids within the interior, so it is believed to be composed of solid rock throughout . Its low bulk density (~ 3346 kg m) indicates a low metal abundance . Mass and moment of inertia constraints indicate that the Moon likely has an iron core that is less than about 450 km in radius . Studies of the Moon's physical librations (small perturbations to its rotation) furthermore indicate that the core is still molten . Most planetary bodies and moons have iron cores that are about half the size of the body . The Moon is thus anomalous in having a core whose size is only about one quarter of its radius . </P>

What are the chemical properties of the moon