Geology of the Moon the Moon. Lunar rocks are in large part made of the same common rock forming minerals as found on Earth, such as olivine, pyroxene, and plagioclase feldspar (anorthosite). Plagioclase feldspar is mostly found in the lunar crust, whereas pyroxene and olivine are typically seen in the lunar mantle. The mineral ilmenite is highly abundant in some mare basalts, and a new mineral named armalcolite (named for "Arm"strong, "Al"drin, and "Col"lins, the three members of the Apollo 11 crew) was first discovered in the lunar samples. The maria are composed predominantly of basalt, whereas the highland regions are iron-poor and composed
Silicate minerals that have been forming and re-working the crust for billions of years. These processes include partial melting, crystallization, fractionation, metamorphism, weathering, and diagenesis. Living things also contribute to this geologic cycle. For example, a type of plankton known as diatoms construct their exoskeletons ("tests") from silica extracted from seawater. The tests of dead diatoms are a major constituent of deep ocean sediment, and of diatomaceous earth. A silicate mineral is generally an ionic solid whose anions consist predominantly of silicon and oxygen atoms. In most minerals in the Earth's crust, each silicon atom is the center of an ideal tetrahedron,