- 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.
- a female given name.
- 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
n.1590s, from Middle French opalle (16c.), from Latin opalus (Pliny), supposedly from Greek opallios, possibly ultimately from Sanskrit upala-s “gem, precious stone.” Used in Middle English in Latin form (late 14c.).
- 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.