Anorthosite

Anorthosite ( /ænˈɔːrθəsaɪt/) is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present.Proterozoic anorthosites were emplaced during the Proterozoic Eon (ca. 2,500–542 Ma), though most were emplaced between 1,800 and 1,000 Ma.Archean anorthosites represent the second largest anorthosite deposits on Earth. Most have been dated between 3,200 and 2,800 Ma, and commonly associated with basalts and/or greenstone belts.The primary economic value of anorthosite bodies is the titanium-bearing oxide ilmenite. However, some Proterozoic anorthosite bodies have large amounts of labradorite, which is quarried for its value as both a gemstone and a building material. Archean anorthosites, because they are aluminium-rich, have large amounts of aluminium substituting for silicon; a few of these bodies are mined as ores of aluminium.Anorthosite from southern FinlandAnorthosite from PolandAnorthosite from the Moon, Apollo 15 'Genesis Rock'