Li+ motion in quartz and β-eucryptite (LiAlSiCO 4) is investigated by dielectric spectroscopy and classical simulations. Simulations are performed using a combination of traditional energy-minimization (using the GULP code) and a mechanical approach derived from Rigid Unit modelling, implemented in the GASP code. Comparison of the simulation approaches shows that geometrical modelling of cooperative framework motions can be combined with electrostatic and Buckingham interactions to give meaningful results for motion of interstitial ions in quartz frameworks. The experimental results can be accounted for on the basis of Li+ motion in the presence of Al substitutional defects.