Differential crystallization of high-magnesian calcites in the cortical spicules and axes of the red coral (Corallium rubrum) correlated to the biochemical compositions of their mineralizing matrices

International audienc

Maîtrise de la ponctuation, maîtrise de la subordination au CM.

Geay J.P., Mas Maurice, Nouet G. Maîtrise de la ponctuation, maîtrise de la subordination au CM.. In: Repères pour la rénovation de l'enseignement du français à l'école élémentaire, n°48, 1978. Recherche – Innovation. pp. 15-34

Nano-crystallization within chemically active glyco- protein hydrogel layers: a possible origin for the long-standing vital effect enigma in the Ca-carbonate skeletons

International audienc

The layered growth and reticulated crystallization of the coral fibers.

International audienc

Biochemical change at the setting-up of the crossed-lamellar layer in Nerita undata (Molluasca, Gastropoda)

International audienceNerita undata is a marine gastropod, the shell of which consists of an external layer composed of very fine, long and undulating calcite prisms, and of an internal aragonite crossed-lamellar layer. As for any Ca-carbonate shell, both layers are composite materials, resulting from the sub-micrometric association of organic macromolecules with the mineral phase. But at the transition between the two layers, in situ synchrotron-based mapping using µ-XANES spectroscopy performed at the S K-edge and SR-FTIR spectroscopy reveals that biochemical compositions change correlatively with the mineral phase, such as displayed by the distribution of sulfur-containing organic compounds (S-polysaccharides or S-amino acids) and organic molecular groups (amide I and II bands). These results highlight the complex change of secretory activity operated by the mineralizing tissue (the mollusk mantle) between these two parts of the shell, which is suspected to minutely control the setting-up of the crossed-lamellar microstructural pattern over the calcite prisms-A not so straightforward feature

The Ca-carbonate biocrystal status in mollusk seashells revisited.

International audienc

Is the pearl layer a reversed shell ? A re-examination of the theory of pearl formation through physical characterization of pearl and shell developmental stages in Pinctada margaritiefera

International audienceA series of physical characterization methods (UV fluorescence microscopy, X-ray microdiffraction, backscattered electron imaging and X-ray absorption spectroscopy) were applied to Polynesian pearls collected after different cultivation periods, varying from three weeks to eighteen months. Through this rigorous time-based sampling, 120 pearls produced by 20 different donor oysters were compared. Results show that the structure of the pearl layer can be understood as a sequence of distinct secretion processes whose progressive occurrence through time may lead to variously arranged and sometimes aberrant mineralized structures. By making comparisons with the structure and growth mode of the Pinctada margaritifera shell, this study shows that the currently accepted theory that views the pearl-bed as a "reversed shell" cannot account for the diversity of the microstructural patterns and mineralogical properties observed in the pearl layers. From a practical and economic view point, it appears that development of these pre-nacreous materials superposed onto a perfectly round-shaped nucleus is the main cause of shape irregularities in pearls and the consequent decrease in their value