Basic elements of crystallography
Polymorphism; Basic principles and characterization methods

Simple bodies, mineral molecules and organic molecules can exist in the form of crystals belonging to the following seven crystal systems: triclinic, monoclinic, orthorhombic, quadratic, rhombohedral, hexagonal and cubic. These systems, which correspond to simple elementary meshes, must be completed by systems corresponding to multiple meshes, i.e. containing more than one node per mesh. This results in the 14 Bravais networks shown in figure 4 , with their characteristics summarized in table 1 .