Earth & SkyGreek → English
Anorthite
/ænˈɔːrθaɪt/noun
The calcium-rich end member of the plagioclase feldspars.
The Greek roots
ἀν-
an-
not
ὀρθός
orthós
straight, upright
Literally: “not straight”
The story of the word
Gustav Rose named it in 1823 for what it is not. Orthoclase feldspar cleaves at a right angle, and its name says so; this mineral's cleavages meet obliquely, so Rose called it the un-straight one. The same ὀρθός insists on straightness in orthodontics, orthopaedics and orthography, all of them promising to correct something crooked.
- How it travelled
- Ancient Greek → scientific coinage → English
- First recorded
- 1823
Same family
orthodoxorthopaedicorthographyorthogonal
In a sentence
The lunar highlands are largely anorthite-rich rock, which is why the moon looks pale.
Under the microscope the anorthite showed the fine twinning typical of plagioclase.