Nacre

The innermost shell layer ( hypostracum ) shell -forming molluscs is called nacre ( mother of pearl ). The biomineral nacre is a composite material made ​​of calcium carbonate and organic matter. The material used animals as a protection against predators. Due to its optical properties ( it shimmers ) it finds in art objects such as jewelry and decorative buttons use.

Occurrence

Mother of pearl is considered by many mollusks, such as oysters, centrifugal screw ( Trochidae ), Turban or round snails ( Turbinidae ), the abalone ( Haliotis ), and the Nautilus ( Nautilus or Burgos also called ) is formed. The colors of mother of pearl vary according to species and geographical background.

Construction

Nacre consists about 95 % of the mineral calcium carbonate (mass fraction ) and up to five percent organic matter. The mineral portion is arranged in a pseudo - hexagonal platelets of 5-15 microns in diameter and 0.5 micron height, wherein the calcium carbonate in the aragonite modification is present. This aragonite platelets are laterally ( in the shell plane ) in layers and arranged vertically in stacks. Between the individual platelets laterally and vertically so-called organic matrix.

Organic matrix

The organic matrix is ​​responsible for the growth and the mechanical properties in the pearl. The structure and role of the organic matrix during the nacre growth is being intensively researched. It is usually divided into water-insoluble and water-soluble matrix, depending on the behavior of the organic fraction after the demineralizing the nacre.

The water-insoluble matrix is ​​the material vertically ( interlamellar matrix ) and lateral ( intertabulare matrix ) is located between the platelets. The interlamellar matrix has a thickness of about 30-50 nm, and has a core of chitin. This chitin is coated on both sides with different proteins, including silk fibroin. The intertabulare matrix, which is located laterally between the platelets, probably consists of collagen or a protein with a similar amino acid composition.

The water-soluble matrix comprises a series (> 10) of proteins, which partially have a strong influence on the crystallization of calcium carbonate.

Optical Properties

The layer structures in the order of the wavelength of visible light. Since at each layer a portion of the incident white light is transmitted and part is reflected, it is interference: Incident and reflected light beams are overlapped so that certain parts of the spectrum of white light will be deleted and, depending on the viewing angle, different shades remain (see a Bragg equation). If the pearl is moving in the light, it therefore seems to shimmer colored ( iridescent ).

Mechanical properties

Mother of Pearl is a typical composite material that can be modeled as similar to a brick wall. Due to the organic material ( " mortar") between the hard but brittle aragonite platelets ( "brick" ) cracks can propagate only at high energy.

Applications

The ground and polished shells of oysters were a common currency material eg in the Polynesian world. Even today, they have not isolated such a role. Another form of currency was the mother of pearl chips in many European casinos until the late 19th century.

Nacre is used for the production of jewelery for a long time because of its iridescent optical properties. For high quality shirt and blouse buttons made of mother of pearl are frequently used. In the northern Thuringian town of Bad Frankenhausen there was a thriving pearl button manufacturing in the 19th century.

For the decoration of furniture and wooden boxes ( inlaid ) next to veneers of exotic woods and mother of pearl tiles were applied. Plays a major role pearl in Chinese lacquer art.

During the construction of high quality musical instruments nacre will still apply. For example, it is used in the construction of guitars and basses as fretboard inlay to the orientation of the frets - so-called "inlays " in the form of blocks or dots. Additionally, the instrument works by noble.

Previously, fish bait made ​​of nacre in use. The prismatic shimmer deceived many predatory fish successfully before a little tidbit. In addition, anglers want these mother-of- bait because pearl is heavy enough to carry him with the rod, together with fishing line far ( enough) out into the lake or the sea.

Mother of pearl as a material for the manufacture of spoons of advantage because it is tasteless in contact with eggs or caviar.

It is investigated whether man-made pearl suitable as a corrosion-resistant protective layer on ship hulls.