Introduction The interactions among ions, water, and a substrate are fundamental processes in fields as diverse as biology, medicine, chemistry, materials science, geology, and space science. The average hydration state of Na + increases with increasing R.H. These sites have different numbers of H 2O molecules coordinating the Na +, and diffusion calculations indicate that they probably occur within the same individual interlayer. For samples exposed to R.H.s from 29% to 100% the spectra show the presence of three hydrated Na + sites that undergo dynamical averaging beginning at −60 ☌. For samples exposed to 0% relative humidity (R.H.), the 23Na spectra show the presence of two Na + sites (probably 6 and 9 coordinated by basal oxygen atoms) that do not undergo dynamical averaging at any temperature from −120 ☌ to 40 ☌. Such motion would cause rippling of the T-O-T structure of the clay layers at frequencies greater than ∼25 kHz. We suggest that the observed dynamical averaging may be due to motion of water volumes comparable to the dripplons recently proposed to occur in hydrated graphene interlayers (Yoshida et al. The results indicate that site exchange occurs within individual interlayers that contain coexisting 1 and 2 water layer hydrates in different places. 23Na MAS NMR spectroscopy of the smectite mineral hectorite acquired at temperatures from −120 ☌ to 40 ☌ in combination with the results from computational molecular dynamics (MD) simulations show the presence of complex dynamical processes in the interlayer galleries that depend significantly on their hydration state.