The densities, refractive indices and compositions of solutions of electrolyte mixtures in quaternary system LiCl + RbCl + MgCl2 + H2O at 323K were determined by isothermal evaporation method. The stereo phase diagram, the metastable phase diagram, the water content diagram, and the diagrams of the physicochemical properties depending on the composition were obtained using the measured data. The metastable phase diagram of this quaternary system contains three invariant points (H-1, H-2, and H-3), seven univariant curves, and five crystallization fields corresponding to single salts lithium chloride monohydrate (LiCl center dot H2O), rubidium chloride (RbCl), magnesium chloride hexahydrate (MgCl2 center dot 6H(2)O), and two double salts: lithium carnallite (LiCl center dot MgCl2 center dot 7H(2)O) and rubidium carnallite (RbCl center dot MgCl2 center dot 6H(2)O). The scope of areas of crystallization of salts is such that RbCl center dot MgCl2 center dot 6H(2)O>RbCl>LiCl center dot H2O>MgCl2 center dot 6H(2)O>LiCl center dot MgCl2 center dot 7H(2)O. The physicochemical properties of the solutions, at equilibrium, change regularly with the change of the concentration of MgCl2. (C) 2014 Published by Elsevier B.V.