Anorthite
Anorthite is the calcium-rich end of the plagioclase feldspar series, common in CAIs, eucrites and the lunar highlands.
Anorthite is plagioclase feldspar at its calcium-rich extreme, with the formula CaAl2Si2O8. Plagioclase is a series between anorthite and albite, the sodium-rich end, and is described by its anorthite percentage, such as An90.
Anorthite-rich plagioclase is typical of rocks from small, dry bodies that lost much of their sodium. Eucrites from Vesta contain plagioclase of roughly An75 to An95, and the bright highlands of the Moon are made largely of anorthosite, a rock of almost pure calcium-rich plagioclase that floated to the top of the early lunar magma ocean. Feldspathic lunar meteorites are samples of this ancient crust.
Anorthite also occurs in calcium-aluminium-rich inclusions. Because it can hold aluminium, it has been used to look for the decay products of aluminium-26, helping to date CAIs and to show how much of that short-lived isotope the early Solar System contained.
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