Since the Cambrian, biominerals contribute to the adaptation of living organisms to different environments by fulfilling various functions including support, locomotion, aggression, protection, camouflage, magnetic navigation, mastication, gravity sensor, and vision. These functions are necessarily associated with adapted morphologies. One of the aims of this project is to contribute understanding how organisms make these complex morphologies. A major difference between biogenic and inorganic calcites is that the former contain almost invariably a small proportion of organic matter. The working hypothesis of our project is that organic molecules play a major role in biomineral structuring at the nanoscale, and that biominerals are true organic/inorganic nanohybrids. However, even if many studies have been dedicated to determining the complex nature of OM, little is known about the structural relationships between OM and crystal: is OM present as inclusions without interaction with the crystal or is it structurally linked to calcite? The aim of this project is to explore the physical relationships between organic molecules and crystal surfaces (and volumes) in biominerals. For this purpose we plan to characterize and understand the nature of OM/crystal interactions in calcitic biominerals using a combination of direct and inverse methods. The direct approach encompasses (1) the synthesis of calcite in solution, in the presence of model organic molecules, and (2) the study of the behavior of model organic molecules (polyenes) on cleaved calcite faces. The inverse method includes the study of some model biominerals (precious corals of the Corallium genus, and selected mollusks with one or more calcitic shell layers such as Pinna or Crassostrea genera. For this project, we will use (sometimes develop) complementary sophisticated techniques involving a range of spectroscopic methods, ultra-high vacuum scanning probe microscopy, atomic force microscopy with antibody-functionalized tips, and synchrotron micro- and nano-tomographies. The consortium involves three geographical and administrative entities and four research groups: SOLEIL (Gif/Yvette), CINaM (Marseille), Biogeoscience and ICB (both at Dijon), at the interface between mineralogy, biology, and physics, combining technical expertise and knowledge on both organic and inorganic parts of biominerals. The organic/inorganic interface is a promising field of research in almost all scientific disciplines. In Earth and Materials Sciences the study of biominerals has implications on the origin and evolution of life, ecology of marine environments, paleoenvironments, paleoclimatology, and elaboration of new efficient and sustainable materials with tailored mechanical properties by soft chemistry.