9.15: Twinning by inversion
The symmetry operation relating pairs of domain structures twinned by inversion may be represented by inversion through a point or by some other isometry equivalent to inversion under the point symmetry group of the domain structure. A two-domain-structure twin that is twinned by inversion is called an inversion twin , but this term is not appropriate when there are more than two domain structures. Twinning by inversion can only occur in non-centrosymmetric structures.