Studies on molluscan shells: contributions from microscopic and analytical methods.

Molluscan shells have always attracted the interest of researchers, from biologists to physicists, from paleontologists to materials scientists. Much information is available at present, on the elaborate architecture of the shell, regarding the various Mollusc classes. The crystallographic characterization of the different shell layers, as well as their physical and chemical properties have been the subject of several investigations. In addition, many researches have addressed the characterization of the biological component of the shell and the role it plays in the hard exoskeleton assembly, that is, the biomineralization process. All these topics have seen great advances in the last two or three decades, expanding our knowledge on the shell properties, in terms of structure, functions and composition. This involved the use of a range of specialized and modern techniques, integrating microscopic methods with biochemistry, molecular biology procedures and spectroscopy. However, the factors governing synthesis of a specific crystalline carbonate phase in any particular layer of the shell and the interplay between organic and inorganic components during the biomineral assembly are still not widely known. This present survey deals with microstructural aspects of molluscan shells, as disclosed through use of scanning electron microscopy and related analytical methods (microanalysis, X-ray diffraction, electron diffraction and infrared spectroscopy). These already published data provide relevant information on shells and also contribute for better understanding the biomineralization process.