Process for making theta-1 zeolite

A process for producing a crystalline aluminosilicate having the following composition in terms of the mole ratios of the oxides:

• 0.9.+-.0.2 M.sub.2 O.sub.n :Al.sub.2 O.sub.3 :xSiO.sub.2 :yH.sub.2 O
• wherein M is at least one cation having the valence n, x is at least 10 and y/x is between 0 and 25, said aluminosilicate in the calcined hydrogen form having an x-ray diffraction pattern substantially as set forth in Table 1 of the specification, which process comprises mixing a source of silica, a source of alumina, a source of alkali metal(s), water and diethanolamine until a homogeneous gel is formed, wherein in the mixture the silica to alumina mole ratio is greater than 40:1, the free alkali metal(s) hydroxide to water mole ratio is greater than 2.times.10.sup.-3 :1, the mole ratio of silica to alkali metal(s) oxide or hydroxide is in the range 1:1 to 20:1 and the mole ratio of water to silica is in the range of 4:1 to 50:1, and crystallising the mixture at a temperature above 70.degree. C., for a period of at least 2 hours.