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1 Université Paul Cézanne and CRMCN-CNRS, UPR 7251, Campus Luminy, Case 913, 13288- Marseilles cedex 9, France
2 UMR 8148 IDES, Bat. 504, Université Paris XI, 91405 Orsay cedex, France
* E-mail: jean-pierre.cuif{at}u-psud.fr
Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to investigate the fine structure of the calcite prisms from the pearl-oyster shell Pinctada margaritifera. The AFM analysis shows that the prisms are made of densely packed circular micro-domains (in the 0.1 µm range) surrounded by a dense cortex. The TEM images and diffraction patterns allow the internal structure of the micro-domains to be described. Each of them is enriched in Ca-carbonate. Hosted in distinct regions of each prism, some are fully amorphous, and some others fully crystallized as subunits of a large calcite single crystal. At the border separating the two regions, micro-domains display a crystallized core and an amorphous rim. Such a border probably marks out an arrested crystallization front having propagated through a previously bio-controlled architecture of the piling of amorphous micro-domains. Compared to recent data concerning the stepping mode of growth of the calcite prisms and the resulting layered organization at the µm-scale, these results give unexpected views regarding the modalities of biocrystallization.
KEYWORDS: biomineralization, atomic force microscopy, transmission electron microscopy, amorphous calcium carbonate
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