A synthetic porous zeolite, identified as ZSM-57, a method for its preparation and use thereof in catalytic conversion of organic compounds are disclosed. The crystalline zeolite has a molar ratio of XO,: Y,O, of at least 4, wherein X represents silicon and/or germanium and Y represents aluminum, boron, chromium, iron and/or gallium and the characteristic X-ray diffraction shown in Table 1. The silica/alumina form of this crystalline material may be prepared with a directing agent in the form of a N,N,N,N'.N',N'-hexaethylpentane-diammonium compound.