Unusual Micrometric Calcite-Aragonite Interface in the Abalone Shell Haliotis (Mollusca, Gastropoda)

Species of Haliotis (abalone) show high variety in structure and mineralogy of the shell. One of the European species (Haliotis tuberculata) in particular has an unusual shell structure in which calcite and aragonite coexist at a microscale with small patches of aragonite embedded in larger calcitic zones. A detailed examination of the boundary between calcite and aragonite using analytical microscopies shows that the organic contents of calcite and aragonite differ. Moreover, changes in the chemical composition of the two minerals seem to be gradual and define a micrometric zone of transition between the two main layers. A similar transition zone has been observed between the layers in more classical and regularly structured mollusk shells. The imbrication of microscopic patches of aragonite within a calcitic zone suggests the occurrence of very fast physiological changes in these tax

Limpet Shells from the Aterian Level 8 of El Harhoura 2 Cave (Témara, Morocco): Preservation State of Crossed-Foliated Layers

International audienceThe exploitation of mollusks by the first anatomically modern humans is a central question for archaeologists. This paper focuses on level 8 (dated around * 100 ka BP) of El Har-houra 2 Cave, located along the coastline in the Rabat-Témara region (Morocco). The large quantity of Patella sp. shells found in this level highlights questions regarding their origin and preservation. This study presents an estimation of the preservation status of these shells. We focus here on the diagenetic evolution of both the microstructural patterns and organic components of crossed-foliated shell layers, in order to assess the viability of further investigations based on shell layer minor elements, isotopic or biochemical compositions. The results show that the shells seem to be well conserved, with microstructural patterns preserved down to sub-micrometric scales, and that some organic components are still present in situ. But faint taphonomic degradations affecting both mineral and organic components are nonetheless evidenced, such as the disappearance of organic envelopes surrounding crossed-foliated lamellae, combined with a partial recrystallization of the lamellae. Our results provide a solid case-study of the early stages of the diagenetic evolution of crossed-foliated shell layers. Moreover, they highlight the fact that extreme caution must be taken before using fossil shells for palaeoenvironmental or geochronological reconstructions. Without thorough investigation, the alteration patterns illustrated here would easily have gone unnoticed. However, these degradations are liable to bias any proxy based on the elemental, isotopic or biochemical composition of the shells. This study also provides significant data concerning human subsistence behavior: the presence of notches and the good preservation state of limpet shells (no dissolution/recrystallization, no bioerosion and no abrasion/fragmentation aspects) would attest that limpets were gathered alive with tools by Middle Palaeolithic (Aterian) populations in North Africa for consumption

Les matériaux biomimétiques

Les matériaux du vivant présentent souvent des propriétés mécaniques remarquables, inégalables en laboratoire en raison de leurs conditions très particulières d’élaboration. Nombre d’entre eux sont des matériaux composites, alliant phases organique et minérale, dont l’organisation structurale est hiérarchisée. La biominéralisation est un des processus constitutifs de ces matériaux où, comme dans la nacre, une phase cristalline croît en interaction avec une matrice organique. La tentative de reproduire ces conditions de minéralisation au laboratoire dans des systèmes modèles simples conduit à proposer différents scénarios et modèles de couplage que cet article passe en revue, en se focalisant essentiellement sur les matériaux analogues à la nacre

CaCO3 nanostructured crystals induced by nacreous organic extracts

International audienceNanostructured CaCO3 crystals are produced in vitro by adding the acid-soluble organic matrix (SOM) extracted from the nacreous layer of Pinctada margaritifera pearl oyster shell to a supersaturated solution of calcium carbonate. For SOM concentrations above 25 ppm, the produced calcite crystals show two structural features of nacre and, more generally, of calcareous biocrystals: structuring at the nanometer scale and a hierarchical structure at higher scales. More specifically, the produced polycrystals exhibit hierarchical structures with stacks of mineral layers, the thickness of which is about 200–400 nm. AFM and SEM microscopies supplemented by FTIR spectrometry allowed us to conclude that these nanostructured layers correspond to packed ‘nanograins’ embedded in an organic matrix. Besides, each layering plane exhibits a single crystal character under TEM and SAED characterizations and can be indexed to the {110} planes of calcite. The reported work sheds light on the crucial role of SOM in the formation of oriented nanostructures, which are generally observed in biological calcareous tissues, like nacre

Calcium carbonate films synthesized via a PILP process for the understanding of biogenic crystals formation

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Multiscale Surface Self-Assembly of an Amyloid-like Peptide

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ANYL 176-Nanostructured interfacial self-assembly of an amyloid-like peptide

235th American-Chemical-Society National Meeting, New Orleans, LA, APR 06-10, 2008International audienceno abstrac

Unusual Micrometric Calcite-Aragonite Interface in the Abalone Shell Haliotis~Mollusca, Gastropoda!

International audienceSpecies of Haliotis (abalone) show high variety in structure and mineralogy of the shell. One of the European species (Haliotis tuberculata) in particular has an unusual shell structure in which calcite and aragonite coexist at a microscale with small patches of aragonite embedded in larger calcitic zones. A detailed examination of the boundary between calcite and aragonite using analytical microscopies shows that the organic contents of calcite and aragonite differ. Moreover, changes in the chemical composition of the two minerals seem to be gradual and define a micrometric zone of transition between the two main layers. A similar transition zone has been observed between the layers in more classical and regularly structured mollusk shells. The imbrication of microscopic patches of aragonite within a calcitic zone suggests the occurrence of very fast physiological changes in these taxa

Développement d'une cellule liquide avec contrôle hydrodynamique pour la microscopie de rayons X en transmission

International audienceLes études spectro-microscopiques dans la gamme spectrale des rayons X couvrant les seuils d'absorption du C, K, Ca, N et jusqu'à l'O, appelée «fenêtre de l'eau », présentent un intérêt particulier pour les systèmes bio-physico-chimiques hydratés, en phase liquide et pour les interfaces liquide/solide. La longueur d'atténuation des rayons X dans l'eau dans cette gamme d'énergie permet l'utilisation de cellules fermées avec des épaisseurs des quelques microns. La complexité de la mise en place de ce type d'environnement est liée à la difficulté de faire coexister un système hermétiquement fermé, situé dans une chambre à vide, avec les exigences de transparence nécessaires pour les mesures en transmission des photons X. Nous présentons ici le design d'une cellule (Fig. 1) dédiée à l'étude des liquides et des interfaces liquide/solide, ainsi que les tests préliminaires réalisés avec le microscope STXM (Scanning Transmission X-ray Microscope) de la ligne de lumière HERMES du synchrotron SOLEIL. Le design sera détaillé en soulignant les choix techniques en lien avec les contraintes fluidiques et d'utilisation du microscope.Nous démontrons ensuite, pour la première fois à notre connaissance, un parfait contrôle hydrodynamique de la cellule (Fig. 2). Pour cela un système de contrôle microfluidique commercial , par pressurisation d'un gaz (azote, dans notre cas), a été choisi pour l'actuation des liquides. Des mesures tests ont mis en évidence la possibilité d'un échange de liquide sans mélange décelable. Plus encore, des premiers tests utilisant des électrovannes contrôlées ont démontré la possibilité de réduire le temps d'échange du liquide de la cellule d'un facteur > 50. De cette manière, et grâce à une gestion des signaux TTL entre la mesure STXM et l’ouverture de ces électrovannes, nous pouvons envisager des schémas de mesure plus complexes