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

Structural, mineralogical, and biochemical diversity in the lower part of the pearl layer of cultivated seawater pearls from Polynesia

A series of Polynesian pearls has been investigated with particular attention to the structural and compositional patterns of the early developmental stages of the pearl layer. These initial steps in pearl formation bear witness of the metabolic changes that have occurred during the pearl-sac formation. The resulting structurally and biochemically complex structures have been investigated using a variety of techniques that provide us with information concerning both mineral phases and the organic components. Results are discussed with respect to our understanding of the biomineralization mechanisms, as well as for the grafting process

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

Caractérisations biochimiques des composés organiques des biominéraux carbonatés

Les biominéraux représentent une importante part des carbonates terrestres et possèdent des propriétés physico-chimiques particulières, liées aux mécanismes intervenant lors de leur cristallisation. Ces spécificités font qu'ils ont de nombreuses applications dans des domaines qui vont de la pharmaceutique à l'aquaculture, de la paléontologie à la physique des matériaux. Afin d'expliciter ces phénomènes, la caractérisation des biominéraux d'un point de vue structurel et chimique est nécessaire. Pour cela, diverses techniques analytiques ont été utilisées en combinaison. Une attention particulière a été portée à la composition chimique des lipides, qui sont une classe moléculaire pour laquelle les données sont quasiment inexistantes. La mise en place de protocoles analytiques destinés à l'étude des lipides combinée à des méthodes préexistantes a non seulement permis de prouver leur existence dans les biominéraux, mais également d'en identifier certains. De plus, la structure lamellaire croisée montre une similarité de composition en lipides, alors que ce n'est pas le cas pour les sucres ou les protéines. Les lipides semblent donc posséder un rôle structural pour ce type d'organisation. La comparaison des lipides d'échantillons fossiles et de leurs équivalents actuels montre par ailleurs qu'ils ne subissent que peu de dégradations lors de la diagenèse, ajoutant la possibilité d'un rôle de maintien des structures aux actions supposées de ces molécules. L'ensemble de ces considérations ouvre donc un nouveau terrain d'études pour la compréhension des mécanismes biologiques et de fossilisation des biominéraux, ainsi que pour les reconstitutions paléo-environnementales.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Les marchés gratuits de Combrailles

International audienceDepuis septembre 2013, nous avons lancé les marchés gratuits dans les Combrailles à fréquence trimestrielle. Nous nous sommes particulièrement attachés, par l'observation, par des discussions ou par des questionnaires, aux comportements des gens face à cette gratuité nouvelle. Nous vous proposons ici un aperçu de cette initiative avec nos premières analyses des comportements face à la gratuité

Pearls defects evidenced by EPMA, EDS and coupled SEM-μ-Raman spectroscopies.

International audiencePearls (Hyriopsis cumingii) are produced from a natural biomineralisation process controlled by organic molecules. Pearl biocrystal is a hybride composite organic / mineral (3 % / 97 %). The regular form of pearl mineralization is aragonite, a hexagonal polymorph of calcium carbonate. This biocarbonate shape is a stack of nanometric thickness hexagonal plates stacked along the c-axis of the aragonite crystal. It diffracts as a single crystal so called MESOCRISTAL. This mineralization produces well-known shiny and "pearly" aspect. Sometimes, pearls show a biomineralisation defect characterized by a lack of shine (also called "milky pearl"). It has been established that this defects is related to the change in mineralization form from hexagonal aragonite to orthorhombic vaterite. SEM images and Raman spectra acquired in the SEM are used to characterize the biocrystals structure of both regular and defective nacre of pearls. The mineralization growth process was also investigated coupling cathodoluminescence (CL) imaging with EPMA mapping. Growth rings were evidenced this way, related to a daily alternation, either side of the interface, i.e. in vaterite and aragonite. EPMA is used for mapping and quantifying trace elements on the same banded structure: CL signal in both aragonite and vaterite is connected to Manganese traces (few hundreds of ppm). Higher Mn contents are observed in vaterite zone compared to that of aragonite

Pearls defects evidenced by EPMA, EDS and coupled SEM-μ-Raman spectroscopies.

International audiencePearls (Hyriopsis cumingii) are produced from a natural biomineralisation process controlled by organic molecules. Pearl biocrystal is a hybride composite organic / mineral (3 % / 97 %). The regular form of pearl mineralization is aragonite, a hexagonal polymorph of calcium carbonate. This biocarbonate shape is a stack of nanometric thickness hexagonal plates stacked along the c-axis of the aragonite crystal. It diffracts as a single crystal so called MESOCRISTAL. This mineralization produces well-known shiny and "pearly" aspect. Sometimes, pearls show a biomineralisation defect characterized by a lack of shine (also called "milky pearl"). It has been established that this defects is related to the change in mineralization form from hexagonal aragonite to orthorhombic vaterite. SEM images and Raman spectra acquired in the SEM are used to characterize the biocrystals structure of both regular and defective nacre of pearls. The mineralization growth process was also investigated coupling cathodoluminescence (CL) imaging with EPMA mapping. Growth rings were evidenced this way, related to a daily alternation, either side of the interface, i.e. in vaterite and aragonite. EPMA is used for mapping and quantifying trace elements on the same banded structure: CL signal in both aragonite and vaterite is connected to Manganese traces (few hundreds of ppm). Higher Mn contents are observed in vaterite zone compared to that of aragonite

Freshwater pearls as near single crystals for vaterite structure resolution

International audienceThere has been lots of controversies about vaterite structure in the past decades. Extra peaks occurring out of the hexagonal structure and best described by Kamhi [1] still resist any indexing. Lower space group symmetries, superspace groups, microtwinning, and first-principle calculations [2], all failed in taking account of these minor peaks, surprisingly always present in all synthetic and biogenic vaterite formations. Recently, secondary interspersed domains observed in high-resolution TEM images indicated their incoherence and rather incompatible character with the vaterite matrix [3]. One of the major difficulty in resolving the vaterite structure lies in the absence of single crystals. Powder diffraction patterns are always composed of hexagonal and extra, but small, peaks, and temptation to index the pattern as a single phase is large, particularly since x-ray fluorescence invariably probes for CaCO3. We used Hyriopsis cumingii freshwater mussel pearls to help proving that vaterite is definitely crystallizing within the original hexagonal space group. Some of these pearls suffer defective growth toward vaterite. In such cases the hexagonal peaks clearly exhibit a strong texture while the extra peaks look more random. This is an invaluable evidence of the existence of clearly separated phases, though the minor phase (or phases) still resist indexing. The hexagonal structure refinement, thanks to the strong vaterite texture, is obtained with larger resolution than before

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