Anorthite

Although found in abundance, anorthite is not cut into a gemstone often. If you've set your heart on this mineral, don't worry too much about clarity, as the stone isn't usually transparent. Expect to pay a high price for one that is. Facetable-quality material has been found, but it's unsure whether this is anorthite or other minerals from the feldspar group, and it's impossible to tell them apart without scientific equipment. The creation of synthetic anorthite is for research purposes. When purchasing, ask for an authentication certificate from the seller.

Anorthite is a rare compositional variety of plagioclase. It occurs in mafic igneous rock. It also occurs in metamorphic rocks of granulite facies, in metamorphosed carbonate rocks, and corundum deposits. Its type localities are Monte Somma and Valle di Fassa, Italy. It was first described in 1823. It is more rare in surficial rocks than it normally would be due to its high weathering potential in the Goldich dissolution series. It also makes up much of the lunar highlands; the Genesis Rock is made of anorthosite, which is composed largely of anorthite. Anorthite was discovered in samples from comet Wild 2, and the mineral is an important constituent of Ca-Al-rich inclusions in rare varieties of chondritic meteorites.