AY Honors/Shells - Advanced/Answer Key

Template:Redirect Nacre, also known as mother of pearl, is a naturally occurring organic-inorganic composite.

The iridescent nacre of a Nautilus

Description

Nacre is composed of hexagonal platelets of aragonite (calcium carbonate (CaCO₃) crystals) that are 10-20 µm wide and 0.5 µm thick, arranged in a continuous parallel lamina. The layers of platelets are separated by sheets of organic matrix that are 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.

The iridescent appearance of the nacre is due to the fact that the thickness of the aragonite platelets are about 0.5 micrometres, which 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 certain species of mollusk. In these mollusks, nacre is continually deposited onto the inner surface of the animal's shell (the iridescent nacreous layer, commonly known as mother of pearl), both as a means to smooth the shell itself and as a defense against parasitic organisms and damaging detritus.

When a mollusk is invaded by a parasite or is irritated by a foreign object that the animal cannot eject, a process known as encystation entombs the offending entity in successive, concentric layers of nacre. This process eventually forms what we call pearls and continues for as long as the mollusk lives.

Chief sources 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.

Decorative uses

Inlay with nacre tesserae
Bagdad pavilion, Topkapı Palace, Istanbul, Turkey

Both black and white mother of pearl are used for architectural purposes. The natural mother of pearl may be artificially tinted to almost any color. Mother of pearl tesserae may be cut into shapes and laminated to a ceramic tile or marble base. The tesserae are hand-placed and closely sandwiched together, creating an irregular mosaic or pattern (such as a weave). The laminated material is typically 1/16 of an inch thick. The tesserae are then lacquered and polished creating a durable, glossy hard surface.

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.

Clothes & accessories

Mother of pearl buttons can be found on a variety of clothing such as shirts, skirts and coats. Nacre is also used as a decorative feature of watch faces and jewelry. It is very valued.

Musical Instruments

Key touches and various decorations on musical instruments such as saxophones, trumpets, violins and guitars are sometimes made of mother of pearl. It is used as inlays on many guitar fretboards e.g. the Gibson J-200. Synthetic key touches made of Pyralin or similar imitation materials have been affectionately referred to as mother of toilet seat by musicians.

References

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See also

• Ammolite