A white to gray variety of plagioclase feldspar that contains a high proportion of calcium to sodium and occurs in alkaline igneous rocks such as gabbro and anorthosite.
A white or grayish variety of plagioclase, CaAl2Si2O8, found in basic igneous rocks.
A white to gray triclinic mineral of the plagioclase feldspar group. Anorthite is the plagioclase mineral that is richest in calcium and occurs in alkaline igneous rocks such as gabbro. Chemical formula: CaAl2Si2O8.
(mineralogy) A plagioclase feldspar, the final member of the Albite-Anorthite solid solution series. Anorthite is very rare on Earth, but abundant in moon rocks. This is because Anorthite weathers rapidly to clay minerals under atmospheric conditions. Good crystals have been found in lava-digested limestone blocks erupted from Mount Vesuvius.
Origin of anorthite
- From Greek an- not a–1 orthos straight (from its oblique crystals)
From American Heritage Dictionary of the English Language, 5th Edition
- From Ancient Greek "less than straight, not perpendicular" - a reference to the odd angles at which crystals grow.