Moon rocks, collected from the surface of the Earth's only natural satellite, are mainly composed of oxygen, silicon, magnesium, iron, calcium and aluminum, in varying amounts. Other trace elements are also present depending on the region of the moon from which the sample was collected.
The lunar surface is composed entirely of four types of igneous rocks: basalt, anthracite, breccia and lunar soil. The first type, found in the flat plains of the moon known as Maria, is a dark volcanic rock formed from rapidly cooled lava flows. Anthracite, by contrast, is found in the elevated regions of the satellite, made from slowly cooled volcanic flows that formed at different times than basalt. The last two types are formed from compacted and shocked material caused by meteor strikes.