Anorthosite
Anorthosite is a pale igneous rock made almost entirely of plagioclase feldspar; it forms the Moon's bright highlands.
Anorthosite is an igneous rock in which plagioclase feldspar makes up 90 per cent or more of the volume. It is usually pale grey to white. On Earth it is found in some ancient rock formations, but on the Moon it is the main rock of the bright highlands.
Lunar anorthosites are rich in calcium-rich plagioclase, close to anorthite. Their discovery in Apollo samples led to the magma ocean idea: plagioclase crystals floated on a global sea of melt and built a crust tens of kilometres thick. Some ferroan anorthosites have been dated to around 4.3 to 4.5 billion years, among the oldest lunar rocks.
Most lunar meteorites are feldspathic breccias rich in anorthositic material, which shows that highland rock covers much of the Moon. Comparing them with Apollo samples, which were collected near the near-side maria, gives a better picture of the whole lunar crust, including the far side.
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