The diffusion of ammonia vapors into a solution of aluminum nitrate or ferric nitrate results in the precipitation of their respective hydroxides and oxyhydroxides. Polymorphic phase formation of alu- minum hydroxide is controlled by the rate of crystallization. The PXRD patterns of products obtained via vapor phase diffusion revealed that poorly ordered aluminum hydroxide is formed during the ini- tial stages of crystallization. After 8 days, the formation of the bayerite phase of aluminum hydroxide was observed. Upon prolonged exposure to ammonia vapors, bayerite was transformed into gibbsite. The infrared spectrum of the product confirmed the presence of different polytypic phases of aluminum hydroxide. The results demonstrated that the crystal structure of metal hydroxides is controlled by the rate of crystallization, nature of the metal ion, site selectivity and specificity and preparative conditions. The diffusion of ammonia vapors into a solution of aluminum nitrate or ferric nitrate results in the precipitation of their respective hydroxides and oxyhydroxides. Polymorphic phase formation of a-minum hydroxide is controlled by the rate of crystallization. The PXRD patterns of products obtained via vapor phase After 8 days, the formation of the bayerite phase of aluminum hydroxide was observed. Upon prolonged exposure to ammonia vapors, bayerite was transformed into gibbsite. The infrared spectrum of the product of the presence of different polytypic phases of aluminum hydroxide. The results demonstrated that the crystal structure of metal hydroxides is controlled by the rate of crystallization, nature of the metal ion, site selectivity and specificity and preparative conditions.