A process for manufacturing a silicoaluminophosphate molecular sieve, the process comprising the steps of: (a) dissolving a silicon source into in a template at conditions sufficient to form a solution having a silicon concentration of at least 0.05 wt. %; (b) adding at least one aluminium source and at least one phosphorus source to at least a portion of the solution of step (a) to form a synthesis mixture, wherein at least the major portion of the aluminum source and phosphorus source are added to the solution after the solution has reached a dissolved silicon concentration of at least 0.03 wt. %; and (c) treating the synthesis mixture for a period of time with mixing and at a temperature sufficient to form the silicoaluminophosphate molecular sieve, wherein the silicoaluminophosphate molecular sieve comprises at least one intergrown phase of molecular sieves having AEI and CHA framework types, wherein the intergrown phase has an AEI/CHA mass ratio of from about 5/95 to 40/60 as determined by DIFFaX analysis.