Nacre ( NAY -k? r also NAK -r? ), also known as mother of pearl , is an organic inorganic composite material produced by some molluscs as inner skin layers; it also forms an outer layer of pearls. Powerful, tough, and colorful.
Nacre is found in some of the most ancient lineages of bivalves, gastropods, and cephalopods. However, the inner layers in most mollusk shells are porcellaneous, not nacreous, and this usually results in non-irregular shine, or more rarely in non-nacreous color games such as flame structures as found in pearl snails.
The outer layer of pearls and inner layers of pearl shells and freshwater pearl shells are made from nacre. Other mollusk families that have inner nacreous skin layers include marine gastropods such as Haliotidae, Trochidae and Turbinidae.
Video Nacre
Physical Characteristics
Structure and display
Nacre consists of hexagonal aragonite platelets (a form of calcium carbonate) of 10-20 Ã,Âμm in width and 0.5Ã,Âμm thickness set in a continuous parallel lamina. These layers are separated by organic matrix sheets composed of elastic biopolymers (such as chitin, lustrin and silk-like proteins). The fragile platelet mixture and the thin film of this elastic biopolymer make the material strong and resilient, with the modulus of Young 70Ã, GPa (when dry). Strength and resilience may also be due to adhesion by the "brick" arrangement of platelets, which inhibits propagation of transverse cracks. This structure, at various lengths, greatly increases its toughness, making it almost as strong as silicon.
Nacre looks colorful because the thickness of the aragonite platelets is close to the wavelength of visible light. This structure interferes constructively and destructively with different wavelengths of light at different angles, creating a structural color.
The crystallographic points c - are approximately perpendicular to the wall of the shell, but the direction of the other axes varies between groups. The adjacent tablets have been shown to have dramatically different c-axis orientations, generally randomly oriented in ~ 20 ° vertical. In bivalves and cephalopods, the axis points b - towards the growth of the shell, whereas in the monoplacophora it is a -axis leaning in this direction. Interlocking nacre bricks has a major impact on both the deformation mechanism and its toughness. In addition, the mineral-organic interface produces enhanced organic strength and strength interlayers.
Formation
The formation of nacre is not fully understood. The initial onset assembly, as observed in Pinna nobilis, is driven by nanoparticle aggregation (~ 50-80 nm) in an organic matrix arranged in a polycrystalline configuration such as fiber. The number of particles increases consecutively and, when critical packaging is reached, they merge into the initial platelets of nacre. The growth of nacre is mediated by organic, controlling the onset, duration and shape of crystal growth. Aragonite "bricks" individuals are believed to quickly grow to full heights of the nacreous layer, and extend until they adhere to adjacent bricks. This results in a close-packing hexagonal characteristic of nacre. Bricks can be core in randomly dispersed elements in organic layers, well-defined protein settings, or may grow epitaxially from mineral bridges stretching from the underlying tablets. Nacre differs from the fibrous aragonite - the brittle mineral of the same form - in that the growth in c-axis (ie, about perpendicular to the shell, in the nacre) is slow in the nacre, and fast in the fibrous aragonite.
Function
Nacre is secreted by epithelial cells of mantle tissue of various molluscs. The nacre is continuously deposited onto the inner surface of the shell, a colorful nacreous layer , commonly known as mother of pearl . The nacre layer smooths the surface of the skin and helps maintain soft tissue against the parasite and destroys the debris by entering it in successive layers of nacre, forming blister pearls attached to the inside of the shell, or free pearls in the mantle tissue. This process is called encystation and continues during the live mollusc.
In a different molluscs group
The nacre form varies from group to group. In bivalves, the nacre layer is formed from a single crystal in a hexagonal covered package. In gastropods, twin crystals, and in cephalopods, they are pseudohexagonal monocrystals, which are often twins.
Maps Nacre
Commercial sources
The main commercial source of the mother of pearls is pearl oysters, freshwater pearl shells, and to a lesser extent abalone, which is popular because of its robustness and beauty in the second half of the 19th century.
Widely used for pearl buttons especially during the 1900s, is a large green snail shell Turbo marmoratus and a large top snail, Tectus niloticus . The international trade in mother-of-pearl is governed by the Convention on International Trade in Endangered Species of Fauna and Flora, an agreement signed by more than 170 countries.
Decorative use
- Nacre has been used for centuries for various decorative purposes
Architecture
Both black and white nacre are used for architectural purposes. Natural nacre may be artificially stained for almost any color. Nacre tesserae can be cut into shape and laminated to ceramic tiles or marble base. The tesserae are hand-placed and tightly together, creating mosaics or irregular patterns (such as weaving). The laminate material is usually about 2 millimeters (0.079 inches) thick. The tesserae is then varnished and polished creating a durable and shiny surface.
Instead of using a base of marble or tile, nacre tesserae can be attached to fiberglass. The result is a lightweight material that offers a seamless installation and no limit to sheet size. The nacre sheet can be used on the interior floor, exterior and interior walls, countertop, door and ceiling. Insertion into architectural elements, such as columns or furniture is easily achieved.
Mode
Mothers of pearl buttons are used in clothing for either functional or decorative purposes. The Pearly Kings and Queens is a complex example of this.
Nacre is also used to decorate watches, knives, weapons, and jewelry.
Musical
Nacre inlay is often used for music keys and other decorative motifs on musical instruments. Many accordions and concertina bodies are completely enclosed in nacre, and some guitars have fingerboard or headstock inlays made of nacre (as well as some guitars have plastic inlays designed to mimic the appearance of nacre). The bouzouki and taslamas (Greek string instruments picked from the harp family) usually feature nacre decorations, as do the associated Middle Eastern oud (usually around the earpiece and on the back of the instrument). Bow string instruments such as violin and cello often have mother in pearl in frog. Traditionally used on saxophone keytouches, as well as trumpet valve buttons and other brass instruments.
More
Mother of pearls is sometimes used to make tools such as spoons for caviar, so as not to damage the taste with a metal spoon.
Produced nacre
In 2012, researchers created calcium-based nacre in the laboratory by mimicking the natural growth process.
Source of the article : Wikipedia
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