Anorthite
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Anorthite is the calcium endmember of the plagioclase feldspar mineral series. The chemical formula of pure anorthite is CaAl₂Si₂O₈. Anorthite is found in mafic igneous rocks. Anorthite is rare on the Earth but abundant on the Moon. Wikipedia
Cleavage: Perfect, good, poor
Melting point: 1553 °C
2V angle: 78° to 83°
Birefringence: δ = 0.012–0.013
Color: White, grayish, reddish
Crystal class: Pinacoidal (1); (same H-M symbol)
Crystal habit: Anhedral to subhedral granular