Hexagonal zinc sulfide crystals were obtained by controlled cooling of melted zinc sulfide. Both pure and activated zinc sulfide powders were used. The density of pure melt grown crystals was found to be higher than that of natural zinc blende crystals or crystals grown by evaporation. The stability of the pure hexagonal crystals towards transformation to the cubic zinc‐blende structure in the interval of temperature 700–1150°C was investigated. A full conversion to the cubic phase was never observed. The experimental evidence indicates the transition point to be above 1150°C.