International audienceSmectite hydration impacts dynamical properties of interlayer cations and thus the transfer and fate of H2O, contaminants, and nutriments in surficial environments where this ubiquitous clay mineral is often one of the main mineral components. The influence of key crystal-chemical parameters, such as the amount of charge or the presence of fluorine, rather than hydroxyl groups, in smectite anionic framework, on hydration, organization of interlayer species, and related properties has been described for tetrahedrally substituted trioctahedral smectites (saponites). Despite the ubiquitous character of octahedrally substituted smectites, that make most of the world bentonite deposits