The mechanism of oleate interaction with fluorite is investigated through adsorption, electrokinetic, and diffuse reflectance FT-IR measurements coupled with theoretical thermodynamic chemical equilibrium calculations. The adsorption isotherms exhibit an infinite increase in the slope beyond an oleate density of 10 μmole m-2. This adsorption density corresponds to a bilayer formation of oleate by two-dimensional condensation with a reported molecular coverage area of 33Ao2 (liquid-crystal state). Comparison of the theoretical chemical equilibria with the experimental data shows that the infinite increase in the slope of the isotherms is due to the precipitation of calcium oleate. The solubility product of this three-dimensional phase is found to be in the pK range 14.4-14.5, and agrees with most of the values quoted in the literature. From IR studies, monocoordination of oleate through counter sodium and calcium ions is suggested for the monolayer filling. ζ potentials of fluorite are correlated to the adsorption of oleate up to bilayer formation, and formation on surface of calcium oleate (three-dimensional growth on substrate) at high oleate concentrations. Two-dimensional condensation of oleate on the fluorite surface followed by the association of hydrocarbon chains (tail-tail bond) for the second layer, prior to the precipitation of calcium oleate in the bulk solution, is proposed as the adsorption mechanism.