Anorthite — exposed in the Royal Ontario Museum, Toronto, Canada — Photo: S. Rae from Scotland, UK · CC BY 2.0
Anorthite
Also known as: Lime feldspar.
Anorthite is the calcium endmember of the plagioclase feldspar mineral series. The chemical formula of pure anorthite is CaAl2Si2O8. Anorthite is found in igneous rocks.
Intro adapted from Wikipedia (CC BY-SA).
Anorthite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca(Al₂Si₂O₈).
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Feldspar structural group.
Key properties: Mohs hardness 6–6.5; specific gravity 2.74–2.76; typically white or gray or colorless; White streak; Vitreous luster; refractive index 1.582; optically biaxial.
IMA symbol An, grandfathered status — known before the IMA’s founding, named in 1823.
A rare constituent of mafic plutonic and volcanic rocks. In some granulite facies metamorphic rocks; in metamorphosed carbonate rocks; with corundum deposits. Known from meteorites.
It is found associated with Olivine, pyroxene, corundum.
Its name comes from the Greek for oblique, for its triclinicity.
Collections: Everyday Minerals.