Definition from Wiktionary, the free dictionary
opal (plural opals)
- (mineralogy) A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity, of the chemical formula SiO2·nH2O.
2012 March 1, Lee A. Groat, “Gemstones”, American Scientist, volume 100, number 2, page 128:
- Although there are dozens of different types of gems, among the best known and most important are […] . (Common gem materials not addressed in this article include amber, amethyst, chalcedony, garnet, lazurite, malachite, opals, peridot, rhodonite, spinel, tourmaline, turquoise and zircon.)
- (biology, genetics, biochemistry) A colloquial name used in molecular biology referring to a particular stop codon sequence, "UGA."
a mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity
- ^ Chambers Dictionary of Etymology, Robert K. Barnhart (ed.), Chambers, 1988
- (mineralogy) opal
declension of opal