In hydrated phyllosilicates the organization of the layers towards each other depends on the interactions between interlayer spaces and layers. Starting from the study, on monocrystals, of rows of reciprocal lattice parallel to c* (particularly for k ? 3n) the type of layers stacking in natural and artificial two-water layer Na-, Ca-and Mg-vermiculites is studied. Two main types of crystalline structure have been found : one related to the Mg-minerals, the other to the Ca-or Na-ones. It is possible to obtain one structure by exchanging the interlayer cation on the other in certain conditions. The Na-and Ca-vermiculites present a la -2 structure (BROWN and BAILEY's nomenclature) i.e. the hexagonal cavities of two adjacent layers lie facing each other. On the other hand, Mg-vermiculites have a structure where each layer is displaced relative to adjacent layers by + b/3. Some hypotheses are drawn up in order to explain the shifts of the layers according to the kind of the exchangeable cation.