Synthesis of large zeolite A and X crystals by a modified Charnell’s method led to the formation of twinned zeolite NaA crystals, overgrowth of NaX onto NaA and co-crystallization of another phase analysed by electron microprobe as a Na aluminosilicate but not yet identified. Single crystals of NaA have a perfect cubic habit with a 100 μm edge. Twinned crystals of NaA are of the same size and correspond to an intergrowth of two cubes like that found in twinned fluorite crystals. NaX single crystals are octahedral, 220 μm along the [100] direction. Based on the difference in morphology of A and X crystals, epitaxial growth of NaX zeolite on NaA was also clearly identified by scanning electron micrographs. The object of this contribution is to provide topological and structural information on the twinning and epitaxy.
