Mollusk shell

FIGURE 19.15 A photomicrograph of the cross section of the mother-of-pearl lining a mollusk shell. The composite material making up mother-nf-pearl consists of flat crystals of calcium carbonate embedded in a tough, flexible organic matrix that resists cracking. 

FIGURE 19.16 The material used to make this high-performance car protects the driver by making use of a design like that of the mollusk shell in Fig. 19.15. The car is made of composite materials that are stronger than steel. 

Fig. 9.2 8180 vs. depth for mollusk shells from a 17.4m-long drilling core from the Caribbean Sea showing systematic variation with time. Each of the saw-tooth patterns lasts 100,000 years and correlates with similar patterns at other ocean locations (Reprinted from Emiliani, C. et al. Earth Planet. Sci. Lett. 37, 349 (1978), copyright 1978 with permission from Elsevier)... 

The dust from mollusk shells can also provoke occupational allergies. Inhalation of mollusk shell dust in a nacre button factory was associated with h)q)ersensitivity pneumonitis (Orriols et ah, 1990, 1997). A similar case was identified in Korea (Kim et ah, 1982). Several Japanese investigators have described occupational asthma occurring among workers who culture oysters (Nakashima, 1969 Wada et ah, 1967). Exposure to dust from mofher-of-pearl in a souvenir maker (Tas, 1972) and fo cuttlefish bones in a jewelry polisher (Beltrami et ah, 1989) was linked to occupational asthma. 

These geochemical tracers have been successfully applied to studies of the shells of a variety of marine organisms including bivalve and gastropod mollusks, ostracods, forams, brachiopods and solitary corals (47, 54, 57, 58). In the case of mollusk shells, for example, serial microsampling around the spiral whorls from earliest to oldest growth revealed sinusoidal variations in isotope ratios, which result from shell deposition in a seasonal environment (47, 50, 62-64). Our previous work showed this to be true of Olivella shells as well, where 8,sO levels fluctuate from warm summer temperatures to cold spring and winter temperatures (38). 

Clark II, G. R. Mollusk shell Daily growth lines. Science 161, 800-802 (1968). 

Addadi, L., Joester, D., Nudelman, F., and Weiner, S. "Mollusk shell formation A source of new concepts for understanding biomineralization processes". Chem. Eur.. 12(4), 981-987 (2006). Ajikumar, P.K., Lakshminarayanan, R., and Valiyaveettil, S. "Controlled deposition of thin films of calcium carbonate on natural and synthetic templates". Crystal Growth Des. 4(2), 331-335 (2004). 

Falini, G., Albeck, S., Weiner, S., and Addadi, L. "Control of aragonite or calcite polymorphism by mollusk shell macromolecules". Science 271(5245), 67-69 (1996). 

Levi-Kalisman, Y., Falini, G., Addadi, L., and Weiner, S. "Structure of the nacreous organic matrix of a bivalve mollusk shell examined in the hydrated state using Cryo-TEM".. Struct. Biol. 135(1), 8-17 (2001). 

Weiner, S., and Traub, W. "X-ray-diffraction study of the insoluble organic matrix of Mollusk shells". FEBS Lett. 111(2), 311-316 (1980). 

Keith, M. L., G. M. Anderson, and R. Eichler Carbon and oxygen isotopic composition of mollusk shells from marine and fresh-water environments. Geochim. cosmochim. Acta 28, 1757 (1964). 

The minerals calcite and aragonite are polymorphs of calcium carbonate. Calcite is the more stable of the two, and aragonite is most often seen in objects made of speleothems, the rocks formed in solution caverns. Aragonite is also an important constituent in many materials of organic origin, such as mollusk shells and the outer skeletons of sand dollars and coral. Calcite is the major component of the rocks limestone and marble, and as such is found in collections as sculpture, building stone, in mosaics, and in inlay or in tarsia. 

Conchiolin is a fibrous protein similar to keratin that is found in mollusk shells, where it is mixed with calcium carbonate. 

Mollusk shells consist of two structural parts, the outer porcelain layer, in which the crystals of calcium carbonate are aligned perpendicular to the outside of the shell, and the thinner inner nacre, in which the crystals are laid down parallel to the inside of the shell (see Figure 5.3). 

Once die meat has been extracted, mollusk shells are usually discarded. Huge middens or piles of clam, oyster, and other shells disclose the appetite people have for these animals. Shells have sometimes been processed, either fresh or from middens, to provide calcium carbonate for a variety of purposes. Calcium carbonate has a huge number of practical uses in medicine, food production, chemicals, cosmetics, building materials, and many more. 

Puka shells originated in Hawaii, where the flat broken tops of worn Conus shells were used as decorations or beads. Beach worn cone shells were often found as concave round fragments with a natural central hole where the spire had broken off. The Hawaiians took this a step further by creating their own pukas out of cone and other mollusk shells that were not quite so worn, but that were the right size and shape to be used as beads. A round shell, usually slightly concave, is drilled in the center and strung as beads. The word puka means hole in Hawaiian. 

The nacre, or smooth inner layer of mollusk shells, is sometimes brightly colored and attractive. Some invertebrate animals have been hunted to nearextinction for their brilliant nacre. An example of this is the Paua shell,... 

Shells, pearls, and other invertebrates may be found in art and anthropology collections as worked objects, or as part of composite objects. The nacreous layer of mollusk shells is commonly referred to as Mother-of-Pearl, and may be found as inlay in objects made of wood and stone, and as small decorative and utilitarian objects such as buttons, jewelry, tool handles, and small carvings. Pearls are used most often in jewelry, drilled through so that they can be strung like beads. They are also used as decoration on fabric and objects d art. 

If preparation of an animal is done too quickly or without proper care, some natural compounds may remain in the specimen. Even though these compounds were liquid when the animal was alive, they may still be toxic. These include venom in the fangs of insects, snakes, some mollusks, and gila monsters. Mollusk shells in a dry collection may contain toxin if the body of the animal was not removed, but rather left to dessicate inside. 

These observations clearly preclude the possibility that the solution from which mineral forms is essentially that of blood or other body fluids, or even sea water. Analyses of fluid extracted from the space in mollusks between the mantle, the organ that forms the shell, and the shell surface, show that it is different from sea water or the blood [86]. It is not, however, clear that this is the actual fluid from which the mineral precipitates. The trace element compositions of the mollusk shell minerals, as well as the shells of many other organisms, are also incompatible with crystallization from a medium similar to sea water [87], indicating that mineral deposition occurs from a specialized medium. 

One of the best understood mineralization systems in terms of the microenvironment of nucleation is the mollusk shell, and in particular one of the seven structural types of mollusk shell, the nacre [99], The nacre has a simple geometry and is therefore a most convenient system to study in terms of nucleation. Observations of growing aragonitic tablet-shaped crystals show that the matrix surface at the location where the first crystals form is different from the remaining surfaces. This location can be differentially stained using dyes that have affinities for calcium and sulfate, for example [100], The surface topography is... 

Broeker, W., "Radiocarbon Dating Fictitious Results with Mollusk Shells, ... 

Despite their monocrystalline habit, the nacreous tablets and the prismatic units of Mollusks shells are composite structures. We do note that these complex structures are rarely visible on simple fractures of the shells, but enzymatic hydrolyzes or/and acidic etchings are effective from this point of view. 

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