Definitions

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

  • n. A variety of feldspar, essentially potassium aluminum silicate, KAlSi3O8, characterized by a monoclinic crystalline structure and found in igneous or granitic rock. Also called potash feldspar.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. Potassium aluminum silicate, KAlSi3O8, a common feldspar of igneous, plutonic, and metamorphic rocks. Orthoclase is the main feldspar of pegmatite occurrences, where it is most commonly flesh-colored. Orthoclase is used in the ceramic and glass industries and as a decorative gravel.

from the GNU version of the Collaborative International Dictionary of English

  • n. Common or potash feldspar crystallizing in the monoclinic system and having two cleavages at right angles to each other. See feldspar.

from The Century Dictionary and Cyclopedia

  • n. Common or potash feldspar, a silicate of aluminium and potassium, occurring in monoclinic crystals and also massive.

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

  • n. a white or colored monoclinic feldspar

Etymologies

Greek ortho-, ortho- + Greek klasis, a breaking (from klān, to break).
(American Heritage® Dictionary of the English Language, Fourth Edition)
ortho- +‎ Ancient Greek κλαστός (klastos, "broken") (Wiktionary)

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