a mineral, an amorphous form of silica, SiO2 with some water of hydration, found in many varieties and colors, including a form that is milky white.
an iridescent variety of this that is used as a gem.
a gem of this.
Other definitions for Opal (2 of 2)
a female given name.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
How to use opal in a sentence
The opal program watches the planets for less than one day a year.The Planets with the Giant Diamonds Inside - Issue 102: Hidden Truths | Corey S. Powell | July 7, 2021 | Nautilus
The rebels then turned their guns on the family huddled in the opal.‘Argo’ in the Congo: The Ghosts of the Stanleyville Hostage Crisis | Nina Strochlic | November 23, 2014 | THE DAILY BEAST
One of the more positive parts of your personal life is your marriage to opal Stone Perlman, which has lasted over three decades.
That clock has four faces made of opal, estimated at a value of $10-20 million.
In that case, at least, Little, Brown responded by pulling opal from the bookshelves.
He owned a 54-ton yacht named the opal, and attributed the wonderful health he enjoyed to his numerous sea voyages.The Recent Revolution in Organ Building | George Laing Miller
If the collodion is good, the film is semi-transparent, of a bluish opal-like appearance.
He fell asleep, and soon and slowly and ever so dimly the opal light of the prairie dawn crept shyly over the landscape.You Never Know Your Luck, Complete | Gilbert Parker
The moon, ringed by a halo, shone like an opal in the milk-white sky.The Child of Pleasure | Gabriele D'Annunzio
He was drinking a dose of sal-volatile, and admiring its opal tint.The Napoleon of Notting Hill | Gilbert K. Chesterton
British Dictionary definitions for opal
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: SiO 2 . n H 2 O
- opal-like, adjective
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Scientific definitions for opal
A usually transparent mineral consisting of hydrous silica. Opal can occur in almost any color, but it is often pinkish white with a milky or pearly appearance. It typically forms within cracks in igneous rocks, in limestones, and in mineral veins. It also occurs in the silica-rich shells of certain marine organisms. Chemical formula: SiO2·nH2O.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.