A porous, crystalline material is described having the framework structure of ZSM-12 and a composition involving the molar relationship: X2O3:(n)YO2 wherein X is a trivalent element, Y is a tetravalent element and n is less than about 45, e.g., less than about 40, wherein the average crystal size of the material is less than about 0.1 micron, which material is substantially free of impurities. The material is made by: (a) preparing a mixture capable of forming said material, said mixture comprising sources of alkali or alkaline earth metal (M), an oxide of trivalent element (X), an oxide of tetravalent element (Y), hydroxyl (OH−) ions, water, and an organic monoquaternary ammonium cation directing agent (R) and an organic diquaternary ammonium structure blocking agent (R′); (b) maintaining the mixture under sufficient conditions until crystals of said material are formed; and (c) recovering the crystalline material from step (ii). The material can be used as a hydrocarbon conversion process catalyst.