The adsorption of fatty acids on sparingly soluble minerals is a complex phenomena due to the fact that fatty acids are capable of forming precipitated phases with dissolved Ca ions from these minerals. A number of mechanisms have been proposed, but none has been fully substantiated. Adsorption and precipitation reactions in alkaline solutions of oleate in the presence of calcite, apatite, fluorite and scheelite have been explained through adsorption isotherms, electrokinetic studies and theoretical thermodynamic chemical equilibria calculations. The adsorption density at monolayer coverage corresponds to the condensed state of alkyl chain (liquid--crystal state) with a molecular coverage area of 33 A exp 2 . The application of two-dimensional condensation model is considered. These studies showed a bilayer formation in the case of apatite, fluorite and scheelite, and a monolayer formation in the case of calcite, prior to the three dimensional condensation of calcium oleate (precipitation) on the substrate