The invention relates to a crystalline zeolite-like gallosilicate having an atomic ratio of Si/Ga in the outer crystalline surface that is not larger than the average Si/Ga ratio for the whole of the crystal. The invention also relates to a method of making such a gallosilicate comprising the hydrothermal crystallization of a strictly inorganic reaction mixture having the following molar ratios: SiO.sub.2 /Ga.sub.2 O.sub.3 .gtoreq.5; OH.sup.- /SiO.sub.2 =0.05-1.0; and H.sub.2 O/SiO.sub.2 =10-1,000. The invention further relates to the above-described method wherein said reaction mixture is prepared by adding an aged gel to a first mixture, the first mixture preferably having a composition with the following molar ratios: SiO.sub.2 /Ga.sub.2 O.sub.3 .gtoreq.5; OH.sup.- /SiO.sub.2 =0.05 to 1.0; and H.sub.2 O/SiO.sub.2 =20 to 100.