Crystallization of calcium sulphate on electrolytic solutions on a heated metal surface was studied in the. laboratory. Using a microscopic method, studies concentrated on the initial period of sulphate scale formation (up to the formation of a compact monolith layer of calcium sulphate on a metal surface). The kinetics and mechanism of nucleation of calcium sulphate crystals were investigated. The activation energy of nucleation and efficient specific surface energy were determined. The effect of a temperature gradient in a solution at the metal surface and its roughness on nucleation of calcium sulphate crystals was estimated.