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Definition of "opal" []

  • A mineral of hydrated silica. (noun)
  • A gemstone made of this mineral, noted for its rich iridescence. (noun)
  • An amorphous, usually iridescent, mineral that can be of almost any colour, found in igneous rocks and around hot springs. It is used as a gemstone. Composition: hydrated silica. Formula: SiO2.nH2O (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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Use "opal" in a sentence
  • "Although opal is not a conclusive indicator of a wetter Mars, it does suggest some interesting scenarios."
  • "The most durable opal is a solid piece, free from fractures."
  • "The very word opal comes from the Sanskrit upala, meaning “precious,” which I guess says it all!"