Nacre

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. It is strong, resilient, and iridescent.

Nacre 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.

Physical characteristics

Structure and appearance

Nacre is composed of hexagonal platelets of aragonite (a form of calcium carbonate) 10–20 µm wide and 0.5 µm thick arranged in a continuous parallel lamina. These layers are separated by sheets of organic matrix composed of elastic biopolymers (such as chitin, lustrin and silk-like proteins). This mixture of brittle platelets and the thin layers of elastic biopolymers makes the material strong and resilient, with a Young's modulus of 70 GPa (when dry). Strength and resilience are also likely to be due to adhesion by the "brickwork" arrangement of the platelets, which inhibits transverse crack propagation. This structure, at multiple length sizes, greatly increases its toughness, making it almost as strong as silicon.

Mother of pearl (disambiguation)

Mother of pearl is a common name for Nacre. It can also refer to:

Mother of Pearl (novel)

See Nacre for material produced by mollusks.

Mother of Pearl (1999) is a novel by Melinda Haynes, and was chosen as an Oprah's Book Club selection, June 1999. The audio version is performed by Nana Visitor.

Plot introduction

Set in Petal, Mississippi, a small town at the close of the 1950s, this novel tells the story of the 28-year-old Even Grade, a black man who grew up an orphan, and Valuable Korner, a 15-year-old white girl, who is the daughter of the town prostitute and an unknown father. They are both separately seeking the family, love, and affection they had not had before, until their paths cross owing to their common acquaintance of loner mystic Joody Two Sun.

Characters in Mother of Pearl