a translucent mineral consisting of hydrated silica of variable color; some varieties are used as gemstones
"The geologist carefully examined the rough opal, noting its unique play of iridescent colors before deciding it was valuable enough to cut into a gemstone."
A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity, of the chemical formula SiO₂·nH₂O.
"The opal displayed its characteristic play of color despite being a softer variety of hydrated silica compared to quartz."
In plain English: An opal is a rare gemstone that displays shifting rainbow colors when light hits it.
"She wore a beautiful opal necklace to the party."
Usage: Do not confuse "opal" with "opals," as the latter is a common pluralization error when referring to multiple stones. The term is also often misused metaphorically for any iridescent object, though it strictly applies only to this specific hydrated silica mineral.
A female given name from English from the precious stone, invented in the nineteenth century.
"The new mother named her daughter Opal after the colorful gemstone."
The word "opal" entered English via French and Latin from the Byzantine Greek opállios, which originally meant a gem or stone in Sanskrit. Its ultimate root traces back to an ancient term for an upper millstone, though it is only distantly related to the modern word "over."