The twin by reticular meriedry occures when the twin symmetry degree is higher than that of the crystalline individuals constituting it, i.e. when the twin network is a multiple of the network of the lonely crystals.
Figure 13 presents a plan of twin as well as the elementary mesh of the twin. Here the index of twin is 3.
Fig. 13 : twins by reticular meriedry
The elements of symmetry defined in the whole building (the twinned crystal), and not belonging to the lonely crystals then act as elements of symmetry of the twin.
This type of twin exists (by multiplicity of the network) only if there is a line perpendicular to the axis of the twin. With the result that this type can exist only for the systems with principal axis (An+->2) when the element of twin is parallel or perpendicular to this axis (6).
In fact, we can observe twin by reticular meriedry only for systems having a ternary symmetry (rhomboedric and cubic), leading to a hexagonal multiple network by rotation of 60° around this axis, which then becomes an axis of rotation of order 6 (fig. 14).
Fig. 14 : Appearance of a hexagonal multiple mesh from cubic elementary meshs.
Cubic system
FLUORINE
The case most representative of this kind of twin by reticular mériedry, is the macle by penetration of the fluorite
The ternary axis of the cubic system [ 111 ] (large diagonal of the cube) (axis of order 6 becomes senary axis), and there is formation of the twinby rotation of 60° around this axis. axe
Fig. 15 : (00.1) fluorite twins 
SPINEL
Another example is the spinel twin which associates by contact two octahedral according to plans a1 (fig. 16).
Fig. 16 : Spinel twin - Mogok Spinels. Burma.
Rhomboedric system
CALCITE
In the rhomboedric system (fig. 17), the simple mesh can take several orientations inside the hexagonal multiple network, which contains 3 rhomboedric simple meshs for 1 hexagonal multiple mesh. There is then formation of twin similar of one's by meriedry, since locally, without changing the total structure of the twin, there is appearance of meshs of different orientations.
Fig. 17 : Twins by meryedry : 2 able positions of the rhomboedric mesh in the hexagonal multiple mesh
Like example of this type of twin, one can quote the macle according to (00.1) of the calcite (fig. 18), for which the plan of contact is parallel with the plan a1 of the rhomboedric crystal.
Fig. 18 : calcite reticuler meriedry twin
Other examples :
diamond, copper, money, gold, crystal...
In very many cases, the continuity of the network which determines the possibility of existence of a twin is only approximate.