The precipitation of barium sulfate (barite) in aqueous solutions of ionic liquids (ILs) has been used as a model system to derive fundamental relationships between crystal nucleation phenomena and some properties of those liquid salts. A systematic dependence between the size of the precipitating crystalline particles and the limiting molar conductivity of ILs has been found. The unraveled correlation has been interpreted in the light of the effect of ILs on water structure dynamics in hydration shells of barite building units and in the bulk solution and respective consequences for crystal nucleation. The response of the crystal formation process to the presence of specific ILs has been used to extract information about some particular properties of ILs (ion association and hydration) that modify the crystal hydration environment.