The z potentials and the streaming potential coefficients of silicate mineral-water and rock-water systems were measured for purposes of estimating the magnitude of electrokinetic effects induced by water diffusion in the earth's interior. In rock-water systems the adsorption reaction of H+ at a solid surface is proved to be a main factor determining the z potential. For typical crustal rocks the z potential in water of pH higher than 2 is commonly negative and increases in absolute magnitude as supporting electrolyte concentration decreases and as temperature increases. A physiochemical theory was developed on the above features of the z potential on the basis of the adsorption reaction at the solid-liquid interface. The experimental and theoretical results obtained in the present study of the z potential and the streaming potential coefficient in rock-water systems are applied to some geophysical problems: electromagnetic variations induced by water diffusion prior to earthquakes and the self-potential anomaly associated with hydrothermal convection.