Nacre vs. Opal — What's the Difference?

Nacre ( NAY-kər also NAK-rə), also known as mother of pearl, is an organic–inorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent.

Opal is a hydrated amorphous form of silica (SiO2·nH2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals.

See mother-of-pearl.

A gemstone consisting of a form of hydrated silica, typically semi-transparent and showing many small points of shifting colour against a pale or dark ground

(obsolete) A shellfish which contains mother-of-pearl.

A mineral of hydrated silica.

A pearly substance which lines the interior of many shells; mother-of-pearl.

A gemstone made of this mineral, noted for its rich iridescence.

A pearly substance which lines the interior of many shells, and is most perfect in the mother-of-pearl.

(mineral) A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity, of the chemical formula SiO₂·nH₂O.

Having the peculiar iridescence of nacre, or mother-of-pearl, or an iridescence resembling it; as, nacré ware.

(gemology) A precious gem, an iridescent gemstone found in the opal-silica mineral substrate (potch)

The iridescent internal layer of a mollusk shell

A colloquial name used in molecular biology referring to a particular stop codon sequence, "UGA."

Any of various lycaenid butterflies of the genus Nesolycaena.

A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity.

A translucent mineral consisting of hydrated silica of variable color; some varieties are used as gemstones