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anorthosite




lunar anorthosite
Lunar anorthosite, Apollo 16
Image credit: NASA

A coarse-grained basic igneous rock made largely of plagioclase feldspar (95%), with small amounts of pyroxene (4%), olivine, and iron oxides. Usually light in color, it may have bands of darker minerals. Anorthosite forms deep underground, and in dikes and intrusions; it makes up about 60% of the Earth's crust. Anorthosite was found in all the rocks returned from the Moon, including the oldest (dating back 4.4 to 4.5 billion years), and is believed to make up a significant fraction of the lunar crust.


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   • GEOLOGY AND PLANETARY SCIENCE