Laboratory experiments were conducted to determine the effects of tar sand process waters on the mineral components of a Utah sandstone (from a known tar sand deposit) and control samples of feldspars of varying compositions. Contact with the process water increased the porosity and permeability of the test samples, which was caused by dissolution of aluminosilicate and carbonate minerals; there was a corresponding precipitation of clay minerals. Once mobilized, ions from the dissolved mineral matter can be moved by a processing wave and later precipitated as clay minerals when geochemical conditions change. Clay minerals can occlude porosity, affecting processing design and efficiency; additionally, they cause disposal and water recycling problems. 23 refs., 69 figs., 5 tabs.