X-ray precession photographs and optical investigations of TPA-ZSM-5 (silicalite) and TEA-ZSM-8 zeolites reveal that ZSM-8 consists of two interpenetrating species rotated by 90 degrees round the crystallographic c axis similarly to ZSM-5. The c axis of ZSM-5 coincides with refractive index n(x), the c axis of ZSM-8 coincides with n(y). The intergrowth species are differently shaped in ZSM-5 and ZSM-8. ZSM-5 consists of an orthorhombic prism penetrated by two pyramidal fragments. The ZSM-8 crystals studied here consist of species with two-dimensional hourglass-like shapes embedded in orthorhombic prisms The orientations of the optical indicatrices of ZSM-5 and ZSM-8 an identical after calcination, i.e., after removing or decomposing the template. This confirms recent work which showed that the framework structures of ZSM-5 and ZSM-8 are essentially identical.