The paper presents author’s original and literature data on the standard free energy of 31 Sc ions and complexes in aqueous solution. Scandium behavior at the weathering of phyllite shales is physicochemically simulated with the Selector program package. The content of Sc in the shales is close to its average content in the Earth’s crust: 10–3 wt %. Solution in the weathering profile was determined to contain Sc practically only in the form of the hydroxocomplex $${\text{Sc}}({\text{OH}})_{3}^{0}.$$ The dissolved Sc concentrations is controlled by the solubility of its oxide Sc2O3 and phosphate ScPO4 and is lower than 10–9 mol/L.