Anorthosite

Anorthosite is a coarse-grained igneous rock composed almost entirely of plagioclase feldspar, typically labradorite or bytownite, with only minor amounts of mafic minerals such as pyroxene or olivine. It is a unique rock type because of its high feldspar content and is primarily found in large plutonic bodies that formed deep within the Earth's crust. Anorthosites are commonly associated with both ancient Precambrian crustal formations and younger intrusive complexes. Anorthosite forms through magmatic differentiation, where feldspar-rich minerals crystallize and separate from mafic magma. The resulting rock is light in color, usually white to gray, but can have an iridescent blue or green sheen due to the presence of labradorite, a variety of plagioclase feldspar. This shimmering effect, known as "labradorescence," makes certain types of anorthosite valuable as decorative stones. One of the most famous occurrences of anorthosite is on the Moon. The lunar highlands are primarily composed of anorthosite, which formed from the early Moon’s magma ocean as lighter feldspar minerals floated to the surface while denser materials sank. The presence of anorthosite on the Moon provides important insights into planetary differentiation and early crust formation. On Earth, anorthosite deposits are found in regions such as the Adirondack Mountains (USA), the Bushveld Complex (South Africa), and the Stillwater Complex (USA). Some anorthosites are also associated with large layered mafic intrusions and can contain valuable mineral resources, including titanium-bearing minerals such as ilmenite. In summary, anorthosite is a feldspar-rich igneous rock with both geological and economic significance. Its presence on the Moon and Earth helps scientists understand crustal evolution, while its mineral content makes it an important resource in industrial applications.