opal

Etymology

In Florio’s A World of Words 1598 as opale, from French opale, from Latin opalus, from Byzantine Greek ὀπάλλιος (opállios), from Sanskrit उपल (upala, “gem, stone”), from उपरि (upári, “the upper millstone”). Distantly related to over.

noun

1. (mineralogy) A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity, of the chemical formula SiO₂·nH₂O.
   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.) 2012-03, Lee A. Groat, “Gemstones”, in American Scientist, volume 100, number 2, archived from the original on 2012-06-14, page 128
   1. (gemology) A precious gem, an iridescent gemstone found in the opal-silica mineral substrate (potch)
2. (biology, genetics, biochemistry) A colloquial name used in molecular biology referring to a particular stop codon sequence, "UGA."
3. Any of various lycaenid butterflies of the genus Nesolycaena.