Among the variety of microstructural types that can be found within Molluscs shells, intercrossed structures (crossed-lamellar, complex crossed-lamellar and cross-foliated) are by far the most commonly found. They are, however, still poorly documented - mainly due to their complex 3D organization. The majority of biomineralization studies, and the resulting models, are indeed essentially based on simple architectures (such as nacreous or prismatic layers). In order to achieve a better understanding of the fundamental mechanisms that drive the mineralization of such biocarbonates, it is therefore mandatory to check to which extent models developed from « simple » shells stay consistent when applied to more complex microstructural organizations. The present study focuses on intercrossed layers of several Mollusk shells, in order to highlight the various levels of biological control exerted by the organism on their formation and growth. In-situ techniques are used to characterize biochemical compositions, in close correlation with microstructural patterns, as well as fine-scale biocrystallization processes. Some peculiar features of the diagenesis of these microstructures are illustrated, through the study of fossil shells from Patella sp (~100 ky) and Velates perversus (~50 My).
