By digesting glassy tuff with alkaline solutions on the waterbath, the writer obtained sodalite and a zeolitic material. Studying in detail the products obtained by the reactions of glassy tuff with NaCl and NaOH solutions in various concentrations, the writers confirmed the conditions being favourable for crystallization of these materials. The longer the tuff was warmed in more concentrated solutions, the more sodalite was produced. Crystallization of the zeolitic material is favourable in a case of lower concentrations of these solutions. NaOH solution seems to behave as a catalyst for the crystallization courses.