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| − | [[Image:NautilusCutawayLogarithmicSpiral.jpg|thumb|right|250px|The iridescent nacre of a [[Nautilus]] ]] | + | A '''whorl''' is a single, complete 360° turn in the [[spiral]] growth of a [[mollusc]] [[Animal shell|shell]]. A mollusc shell is basically a long tube, usually coiled in a spiral for strength and compactness. The number of whorls in the shell depend on various factors in the geometric growth, as described in work of [[D'Arcy Wentworth Thompson|D’Arcy Wentworth Thompson]] (''[[On Growth and Form]]'') and [[David Raup]]. |
| − | [[image:nacre.jpg|thumb|200px|A piece of nacre]] | |
| − | [[image:Nacre_microscopic_structure.png|thumb|200px|A schematic of the microscopic structure of nacre, showing how the layers of aragonite platelets are separated by protein.]]
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| − | '''Nacre''', also known as '''mother of pearl''', is a naturally-occurring organic-inorganic composite. | |
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| − | About 95 % of nacre consist of layers of [[calcium carbonate]] (CaCO<sub>3</sub>) platelets ([[crystals]]), a weak and brittle ceramic in the form of [[aragonite]] and [[conchiolin]] (a [[scleroprotein]]), separated by [[elastic]] [[biopolymers]] (such as [[chitin]] and [[lustrin]]). Both components are rather weak materials when separate. This mixture of brittle [[nanometer]] 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 [[silicium]].
| + | The number of whorls differs in various groups, with the extant family [[Turritellidae]] and the [[Mesozoic]] family [[Nerineidae]] having very high [[Spire (mollusc)|spired]] shells with a large number of whorls and hence a relatively small [[Aperture (mollusc)|aperture]]. |
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| − | 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.
| + | *'''Apical whorls'''—those whorls near the apex or tip of the shell. |
| | + | *[[Body whorl]]—The most recently formed whorl of a spiral shell. |
| | + | *'''Nuclear whorl(s)'''—small, generally smooth whorls formed within the egg and constituting the apex of the shell. |
| | + | *'''[[Protoconch]]''' a larval shell of a mollusc; also refers to protoconch whorls of an adult shell. |
| | + | *'''Teleoconch'''—all the whorls of a shell after the protoconch whorls. |
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| − | Nacre is secreted by the [[epithelial]] [[cell (biology)|cells]] of the [[Mantle (mollusc)|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 [[parasite|parasitic organisms]] and damaging detritus.
| + | [[Category:Animal anatomy]] |
| − | | + | [[Category:Molluscs]] |
| − | The iridescent inner layer is considered highly attractive by many cultures and is often used in making [[jewelery]] or as inlays in wood [[furniture]] and [[guitar]]s.
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| − | 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 [[pearl]]s and continues for as long as the mollusk lives.
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| − | 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 Ocean|Pacific]] regions.
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| − | ==Decorative uses==
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| − | Tiles: Small, hand-cut shapes with straight edges, called 'tesserae', are laminated to either a [[marble]] or a [[ceramic]] 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.
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| − | Sheets: Instead of using a marble or tile base, the mother of pearl tesserae are 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.
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| − | 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.
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| − | Mother of pearl is also used to clad porcelain sinks. Mother of pearl tesserae may be cut into artistic shapes and be laminated to ceramic tile and surrounded by numerous coats of colored lacquer to create an artistic design. The lacquer and the mother of pearl are polished at the same time, creating a durable, glossy hard surface.
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| − | It is also available in thin laminated sheet form, allowing easy inlay and cladding work, and modern ceramic tiles.
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| − | Shirt buttons were once often made of mother of pearl, though plastic has largely replaced its use. Some of the finer-quality clothing companies (e.g., [[Lacoste (company)|Lacoste]]) still use it, however.
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| − | Key touches and various decorations on musical instruments such as [[saxophone]]s, [[trumpet]]s, and [[guitar]]s are sometimes made of mother of pearl. Synthetic key touches made of [[Pyralin]] or similar imitation materials have been "affectionately" referred to as ''mother of toilet seat'' by musicians.
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| − | ==References==
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| − | *Lin, A., and Meyers, M.A. 2005. Growth and structure in abalone shell, ''Materials Science and Engineering A'' '''390'''(Jan. 15):27–41 ([http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TXD-4DH2DRS-1&_coverDate=01%2F15%2F2005&_alid=256050522&_rdoc=1&_fmt=&_orig=search&_qd=1&_cdi=5588&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=f4efd0a3d7cf3b4a0b8f9861cff4514d ])
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| − | *Mayer, George, "Rigid Biological Systems as Models for Synthetic Composites", ''Science'' '''310''' (18 Nov 2005):1144–1147
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| − | ([http://www.sciencemag.org/cgi/content/abstract/310/5751/1144])
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| − | *{{cite journal2|author = Ortiz C. ''et al.''|year=September 2005|title = Nanoscale morphology and indentation of individual nacre tablets from the gastropod mollusc ''Trochus niloticus''|journal= J. Mater. Res.|volume= 20|issue=9}} [http://web.mit.edu/cortiz/www/Ben/BenPaperRevisedFinal.pdf pdf file on line]
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| − | ==See also==
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| − | {{Wiktionary}}
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| − | * [[Ammolite]]
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| − | [[Category:Mollusc products]] | |
| − | [[Category:Gemstones]] | |
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| − | [[de:Perlmutt]]
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| − | [[es:Nácar]]
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| − | [[fr:Nacre]]
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| − | [[nl:Parelmoer]]
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| − | [[pl:Masa perłowa]]
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| − | [[pt:Madrepérola]]
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| − | [[sv:Pärlemor]]
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| − | [[tr:Sedef]]
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