The synthesis of tetramethylammonium offretite has been studied using potassium hydroxide and tetramethylammonium hydroxide as bases and sodium aluminate and five natural silicates as sources of aluminium. Using a direct crystallization method, the solubility of the silicate controls the nature of the phase produced. Under the same conditions, offretite is obtained from kaolinite and calcined silicates whereas uncalcined perlite, montmorillonite, beidellite and hall halloysite lead to phillipsite, hydroxysodalite and zeolites W and ZK19, respectively. Aging of the crystallization slurries at room temperature permits the development of offretite nuclei which can be used to direct the crystallization of solutions, free of tetramethylammonium ions and prepared with any silicate, towards pure offretite. The zeolites obtained in this way are silica-rich and contain small quantities of organic ion.