Polarized optical microscopy observations performed on mixtures of Liquid crystals reveal developable domain textures for Twist Grain Boundary (TGB) phases. In these structures, the smectic blocks, the grain boundaries and the layers of helical structure of TGB phase are coiled in a double-twist manner. The energy considerations require that the blocks can just be folded in cones and cylinders, the only surfaces that may be unrolled without elongations. The cones need defects to build up; in particular, a disclination is necessary all along the cone axis. In the N* phase, the field of the chi-director that emanates from the center of the spherulite has the geometry of a hedgehog point defect. The disclination lines of strength k=2 escape into third dimension with no singularity remaining and the chi-director is not materialized. However in TGBA the chi-singularities are materialized as singularities of the slabs.