A method of crystallizing a crystalline molecular sieve having a pore size in the range of from about 2 to about 19 Å, said method comprising the steps of (a) providing a mixture comprising at least one source of ions of tetravalent element (Y), at least one hydroxide source (OH), and water, said mixture having a solid-content in the range of from about 15 wt. % to about 50 wt. %; and (b) treating said mixture to form the desired crystalline molecular sieve with stirring at crystallization conditions sufficient to obtain a weight hourly throughput from about 0.005 to about 1 hr−1, wherein said crystallization conditions comprise a temperature in the range of from about 200° C. to about 500° C. and a crystallization time less than 100 hr.