[en] The crystal lattices and crystal structures of franckeite and cylindrite have been restudied using transmission electron microscopy. The selected-area diffraction, convergent-beam diffraction and high-resolution electron microscopy observations revealed that the relations between the two lattices and between the lattice and the structure modulation are various and incommensurate. Revised structure models of cylindrite and franckeite are proposed from the application of the structural principles found to form the basis of the crystal structure of angitorite for explanation of sinusoidal modulations in these minerals. The simulated and observed high-resolution electron microscopy images match very well. The crystallo-chemistry of cylindrite and franckeite is also discussed. (orig.)