This substance is called "mother of pearl" because it is literally the "mother", or creator, of true pearls.
Nacre is found in certain ancient lineages of bivalves, gastropods and cephalopods. However, the inner-shell layer in the great majority of shelled mollusks is merely porcellaneous and non-nacreous, resulting in a non-iridescent shine like that of a porcelain plate.
Pearls and the inside layer of pearl oyster shells and freshwater pearl mussel shells are made of nacre. Many other families of mollusks also have an inner shell layer which is nacreous, including marine gastropods such as the Haliotidae, the Trochidae and the Turbinidae.
Nacre is composed of hexagonal platelets of aragonite (calcium carbonate (CaCO3) crystals) 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. Strength and resilience are also likely to be due to adhesion by the "brickwork" arrangement of the platelets, which inhibits transverse crack propagation. This design at multiple-length sizes increases its toughness enormously, making it almost equivalent to that of silicon.
Nacre appears iridescent because the thickness of the aragonite platelets is comparable to the wavelength of visible light. This results in constructive and destructive interference of different wavelengths of light, resulting in different colors of light being reflected at different viewing angles.
Nacre is secreted by the epithelial cells of the mantle tissue of some species of mollusk. The nacre is continuously deposited onto the inner surface of the shell, the iridescent nacreous layer, commonly known as mother of pearl. The layers of nacre smooth the shell surface and help defend the soft tissues against parasites and damaging detritus by entombing them in successive layers of nacre, forming either a blister pearl attached to the interior of the shell, or a free pearl within the mantle tissues. The process is called is encystation and it continues as long as the mollusk lives.
Chief sources of mother of pearl are the pearl oyster, found in warm and tropical seas, primarily in Asia; freshwater pearl mussels, which live in many rivers of the United States, Europe, and Asia; and the abalone of California, Japan, and other Pacific regions.
Mother of pearl has been used over many centuries for all kinds of decorative purposes.
Instead of using a marble or tile base, the mother of pearl tesserae can be glued to a fiberglass mesh. The result is a lightweight material that offers a seamless installation, and there is no limit to the sheet size. Mother of pearl sheets may be used on interior floors, exterior and interior walls, countertops, doors and ceilings. Insertion into architectural elements, such as columns or furniture is easily accomplished.
Mother of pearl buttons, also known as "pearl buttons", are used in a decorative or functional way on a variety of clothing such as shirts, sweaters, skirts, jackets and coats.
Pearl buttons as a decoration for clothes are carried to extremes in the costumes of the Pearly Kings and Queens.
Nacre is also used as a decorative feature of watch faces, knives, guns and jewelry.