According to the Lunar Reconnaissance Orbiter Camera website, the moon has a crust that is composed of rocks such as anorthosite and basalt. Anorthosite contains the mineral plagioclase feldspar which gives the rock its light color. The basalt on the moon is dark, because it is mixed with iron-bearing minerals. Basalt contains pyroxene, olivine, volcanic glass and ilmenite.
One difference between lunar basalts and basalts from Earth is that lunar basalts have less iron. According to Washington University, astronauts on the Apollo 11 mission were the first to discover volcanic basalt, also referred to as mare basalt, on the moon. Mare basalt is made up of crystals that form when lava cools, and the amount of time it takes for the lava to cool determines the size of the crystal. After cooling, lava forms into elongated crystals with irregular shapes. Fast-cooling lava produces shorter crystals. Shorter-length crystals are more abundant than longer crystals. The color variation of the crystals comes from the yellow hue of pyroxene and the grey tint of feldspar. Olivine makes the crystals emit bright colors, and ilmenite gives the crystals an opaque quality. The Apollo 11 mission brought mare basalt samples from the Mare Tranquillitatis that were found at various depths on the moon’s surface. The samples were 3.2 to 3.9 billion years old. These basalts are also more volatile than basalts from Earth, because they melt at lower temperatures.