from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A rare plagioclase feldspar with high calcium oxide content occurring in igneous rocks.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. 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.

from the GNU version of the Collaborative International Dictionary of English

  • n. A mineral of the feldspar family, commonly occurring in small glassy crystals, also a constituent of some igneous rocks. It is a lime feldspar. See feldspar.

from The Century Dictionary and Cyclopedia

  • n. A triclinic lime feldspar, found in small transparent crystals on Mount Vesuvius, and existing also as a constituent of some rocks. See feldspar.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. rare plagioclastic feldspar occurring in many igneous rocks


From Greek an-, not; see a-1 + orthos, straight (from its oblique crystals).
(American Heritage® Dictionary of the English Language, Fourth Edition)
From Ancient Greek "less than straight, not perpendicular" - a reference to the odd angles at which crystals grow. (Wiktionary)



Log in or sign up to get involved in the conversation. It's quick and easy.