Difference between revisions of "AY Honors/Shells - Advanced/Answer Key"

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[[Image:Viviparus contectus met operculum2.JPG|right|thumb|[[Gastropod shell]] of ''[[Viviparus contectus]]'' with operculum]]
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{{redirect|Mother of Pearl|the novel|Mother of Pearl (novel)}}
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'''Nacre''', also known as '''mother of pearl''', is an organic-inorganic [[composite material]] produced by some [[mollusk]]s.  It is strong, resilient, and [[Iridescence|iridescent]].  [[Pearl]]s and the inside layers of an oyster shell are made of nacre.
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[[Image:NautilusCutawayLogarithmicSpiral.jpg|thumb|right|225px|The iridescent nacre of a [[Nautilus]] ]]
  
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The '''operculum''' (plural : opercula or operculums) of [[gastropod]]s is a corneous or calcareous structure which exists in some families of snails, and which, in its most typical condition, fits perfectly into the opening or [[aperture (mollusc)|aperture]] of the [[animal shell|shell]]. In life the operculum is attached dorsally to the posterior part of the foot.  
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==Description==
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Nacre is composed of hexagonal platelets of [[aragonite]] ([[calcium carbonate]] (CaCO<sub>3</sub>) [[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 [[Elasticity (physics)|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]].
  
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The operculum grows as the shell grows, so that it stays in proportion. However, in many species of marine shelled snails which live subtidally, the operculum is reduced in size, and no longer serves to completely seal the shell entrance.
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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.
  
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In those species where the operculum completely seals the shell, it can serve as a protection against [[predator]]s when the snail body is retracted. Perhaps its most essential function however is to alllow snails to resist drying out. This is important in intertidal marine snails during low tide, and enables operculate pond and land snails to survive periods of drought, and periods of dry weather.
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Nacre is secreted by the [[epithelial]] [[cell (biology)|cells]] of the [[Mantle (mollusc)|mantle tissue]] of some species of [[mollusk]]. The nacre is deposited onto the inner surface of the shell, the iridescent ''nacreous layer'', commonly known as ''mother of pearl''.  This smooths the shell and defends against [[parasite]]s and damaging detritus by entombing them in successive layers of nacre, forming a [[pearl]]. The process is called is ''[[encystation]]'' and continues while the mollusk lives.
  
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The operculum has a concentric structure, and a nucleus which may be central, or which instead may be situated near the parietal margin of the shell. There are two basic types of opercula:
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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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* The most common kind of operculum is composed of a thin to rather thick corneous protein material, which is yellow to brownish in color and is usually somewhat translucent. This matter is supple. The operculum varies in shape, depending on the family of snails and the shape of the aperture of their shells.
 
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* The other type is restricted to certain families of gastropods. This operculum structure has a corneous base with a heavy calcareous overlay, which in some genera has color or ornamentation of various kinds including for example, pustules and incised grooves.
 
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Opercula may be described as multispiral (having many closely spaced spirals), paucispiral (with few spirals), and the different shapes of opercula can include ungulate (hooflike), claw-like, or ovate. The type and shape of the operculum is used to help identify and classify related groups (genera) of land operculates, and likewise some marine operculates.
 
  
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A few species of shelled land [[Pulmonata|Pulmonates]], such as the edible land snail, ''[[Helix pomatia]]'' sometimes create an '''epiphragm''', which is not an operculum, but in some ways serves in place of one. The epiphragm can be a calcareous septum, or a dried film of mucus, and it is used to seal off the aperture of the shell during [[estivation]].
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== Decorative uses ==
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[[Image:Istanbul.Topkapi046.jpg|thumb|right|200px|<center> Inlay with nacre tesserae </center> <br /> <small> Bagdad pavilion, Topkapı Palace, Istanbul, Turkey </small>]]
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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. Mother of pearl [[:wikt:tessera|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.
  
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<gallery>
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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.
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Image:Helix pomatia operculum hg.jpg|epiphragm of ''[[Helix pomatia]]''
 
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Image:Helix pomatia - epiphragma.jpg|epiphragm of ''Helix pomatia''
 
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</gallery>
 
  
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==Use as incense material==<!-- This section is linked from [[Incense]] -->
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=== Clothes & accessories ===
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Operculum of certain [[gastropods]], especially varieties from the [[Red Sea]], has long served as an [[incense]] material in ancient [[Jew]]ish tradition, as well as in [[Christian]] and [[Arabian]] [[Muslim]] faiths. The operculum of conch species ''[[Strombus|Strombus tricornis]]'' and ''[[conch | Lambis truncata sebae]]'' are most commonly used in regions near the [[middle east]]. Many believe that operculum from these conches is the "'''Onycha'''" incense material described in the Book of [[Exodus]].  
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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 well valued in society and a sign of wealth.
  
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Operculum powder is also an important ingredient to [[China|Chinese]] and [[Japan]]ese incense makers, which are called "''beì xiāng''" (Chinese: 貝香; ''lit.'' sea shell fragrance) or "''kai kou''" (Japanese: 甲香, ''lit.'' shell/armour fragrance) respectively. Incense producers in these countries use the operculum of many conches and other maine [[snail]]s including those found Southeast Asia, South America, and East Africa. Operculum is traditionally treated with [[vinegar]], [[alcohol]] and [[water]] to remove any [[fish]]y smells. The clean opercula are then ground to a powder and used as a scent fixative, in a similar technique to that used in [[perfume]]s with certain plant [[resin]]s.
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=== Musical instruments ===
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Key touches and various decorations on musical instruments such as [[saxophone]]s, [[trumpet]]s, [[violin]]s, [[banjos]], [[tamburitza]]s and [[guitar]]s 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 nacre materials have been affectionately referred to as ''mother of toilet seat'' by musicians.
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When burnt on its own, high quality operculum reportedly smells of [[castoreum]] or other animal [[musk]]s, while that of lower quality is reminiscent of burnt ''hair''.
 
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==Use as a gem==
 
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Operculum as a gem is known as "Shiva's eye". It is collected by divers after the shellfish has died, and is being polished before being used to decorate rings, bracelets, amulets etc.
 
  
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==References==
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* {{cite journal
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| first = A.
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| last = Lin
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| coauthors = Meyers, M.A.
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| date = 2005-01-15
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| title = Growth and structure in abalone shell
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| journal = Materials Science and Engineering A
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| volume = 390
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| pages = 27&ndash;41
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| url = 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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| doi = 10.1016/j.msea.2004.06.072
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}}
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* {{cite journal
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| first = G.
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| last = Mayer
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| year = 2005
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| url = http://www.sciencemag.org/cgi/content/abstract/310/5751/1144
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| title = Rigid biological systems as models for synthetic composites
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| journal = Science
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| volume = 310
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| pages = 1144&ndash;1147
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}}
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* {{cite journal
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| last = Bruet
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| first = B.
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| coauthors = ''et al.''
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| year = 2005
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| month = September
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| title = Nanoscale morphology and indentation of individual nacre tablets from the gastropod mollusc ''Trochus niloticus''
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| journal = J. Mater. Res.
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| volume = 20
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| issue = 9
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| url = http://web.mit.edu/cortiz/www/Ben/BenPaperRevisedFinal.pdf
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| doi = 10.1557/JMR.2005.0273
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}}
  
 
==See also==
 
==See also==
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*[[Operculum]]
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{{Commonscat|Mother of pearl}}
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{{Wiktionary}}
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==References==
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* [[Ammolite]]
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*Burnie, D. (2001). ''[[Animal (book)|Animal: The Definitive Visual Guide to the World's Wildlife]]''. DK Adult Publishing. pg. 24.
 
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==External links==
 
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*[http://www.nansaidh.us/operc/index1.html Pictures of diverse gastropod opercula]. This site also provides fairly extensive material on the growth, development, and physiology of the gastropod operculum as well as hundreds of pictures of both the operculum and its host shell.
 
  
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[[Category:Animal anatomy]]
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[[Category:Mollusc products]]
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[[Category:Incense]]
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[[Category:Pearls]]
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[[Category:Molluscs]]
 
  
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[[cs:Operkulum]]
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[[bg:Седеф]]
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[[de:Operculum]]
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[[da:Perlemor]]
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[[eo:Operkulo]]
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[[de:Perlmutt]]
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[[fr:Opercule]]
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[[eo:Perlamoto]]
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[[nl:Operculum]]
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[[es:Nácar]]
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[[pt:Opérculo]]
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[[fr:Nacre]]
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[[he:אם הפנינה]]
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[[it:Madreperla]]
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[[lt:Perlamutras]]
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[[nl:Parelmoer]]
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[[pl:Masa perłowa]]
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[[pt:Madrepérola]]
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[[ru:Перламутр]]
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[[sv:Pärlemor]]
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[[vi:Xà cừ (vật liệu)]]

Revision as of 00:29, 1 January 2008

Template:Redirect Nacre, also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks. It is strong, resilient, and iridescent. Pearls and the inside layers of an oyster shell are made of nacre.

The iridescent nacre of a Nautilus

Description

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 deposited onto the inner surface of the shell, the iridescent nacreous layer, commonly known as mother of pearl. This smooths the shell and defends against parasites and damaging detritus by entombing them in successive layers of nacre, forming a pearl. The process is called is encystation and continues while 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 well valued in society and a sign of wealth.

Musical instruments

Key touches and various decorations on musical instruments such as saxophones, trumpets, violins, banjos, tamburitzas 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 nacre materials have been affectionately referred to as mother of toilet seat by musicians.

References

See also

Template:Commonscat Template:Wiktionary

bg:Седеф da:Perlemor de:Perlmutt eo:Perlamoto es:Nácar fr:Nacre he:אם הפנינה it:Madreperla lt:Perlamutras nl:Parelmoer pl:Masa perłowa pt:Madrepérola ru:Перламутр sv:Pärlemor vi:Xà cừ (vật liệu)

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