Anorthosite (pronounced /ænˈɔrθəsaɪt/) is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar (90–100%), and a minimal mafic component (0–10%). ilmenite and olivine are the mafic minerals most commonly present.
Anorthosite can be divided into two types: Proterozoic anorthosite (also known as massif or massif-type anorthosite) and Archean anorthosite. These two types of anorthosite have different modes of occurrence, appear to be restricted to different periods in history, and are thought to have had different origins.
Lunar anorthosites constitute the light-coloured areas of the Moon's surface and have been the subject of much research.