Structures with AB 1 CD 1 AB 1 CD 1 stacking in B 6 Se were often observed when the fragment under study contained two twin systems. It is known that when twins in two or more planes appeared in the crystal, they come into contact as the twin layers grow and then pass through each other. This can lead to two effects: one twin system absorbs another or a new phase is formed . As has been shown previously, the layers obtained by twinning can form a new structure . In fact, the twinning mechanism is related to the deformation of the unit cell under an external force, which leads to a change in the orientation of different parts of the crystal. In reality, the evolution of the deformation manifests itself as the appearance and successive propagation of layers of the twin system in the original crystal. For this reason, twinning can also be considered a structure forming process. Crossing of twinned interlayers leads to strengthening of crystalline solids. The twinned interlayers that form under mechanical stresses increase the resistance of crystals to plastic deformation .