Null ellipsometry was used to investigate the adsorption of poly(acrylic acid) (PAA) in the form of sodium poly(acrylate) (NaPA) on polished calcite crystals in aqueous electrolytes at pH 9. The ellipsometric angles were converted into adsorbed mass with an optical layer model, which treats the surface roughness by introducing an additional surface layer. One finds that the adsorbed mass saturates near 4 mg/m2. Higher values of specific adsorbed mass were also observed, and they can be explained with the precipitation of polyelectrolyte with calcium ions.