Nacre (nonfiction)

Nacre gunpowder flask, circa 1750, mostly consisting of the polished shell of a large sea snail Turbo marmoratus.

Nacre (/ˈneɪkər/ nay-kər also /ˈnækrə/ nak-rə), also known as mother of pearl, is an organic-inorganic composite material produced by some molluscs as an inner shell layer; it also makes up the outer coating of pearls.

Nacre is strong, resilient, and iridescent.

It is found in some of the more ancient lineages of bivalves, gastropods, and cephalopods.

However, the inner layer in the great majority of mollusc shells is porcellaneous, not nacreous, and this usually results in a non-iridescent shine, or more rarely in non-nacreous iridescence such as flame structure as is found in conch pearls.

The outer layer of pearls and the inside layer of pearl oyster and freshwater pearl mussel shells are made of nacre.

Other mollusc families that have a nacreous inner shell layer include marine gastropods such as the Haliotidae, the Trochidae and the Turbinidae.