ZSM-22 (TON) can be produced from a potassium based 1,6 hexamethylenediamine (1,6 HDM) synthesis mixture. However, ZSM-34 (an OFF/ERI intergrowth) is synthesized from the same synthesis mixture with the addition of a source of sodium either from colloidal silica combined with sodium hydroxide or from sodium silicate. NMR analyses of the as-synthesized zeolite samples determined the presence of a carbonyl species for all of the ZSM-34 samples, but not for any preparations that produced ZSM-22. The carbonyl species was present in all ZSM-34 preparations regardless of the diamine used (NH 2 C n H 2n NH 2 for n 4, 6, 8, or 10) and was present only after the synthesis mixture was heated above the ambient temperature (even though the gel was still amorphous). The source of the carbonyl may be obtained from the reaction of carbon dioxide preadsorbed in the basic sodium solution with the diamine to form a carbamic acid. Molecular modeling studies, based on pore ®lling, calculated a favorable ®t of the carbamic species within the pore system of the Erionite suggesting a reason for the formation of the OFF/ERI intergrowth.