Crystallographic Merohedral Twinning

Merohedral twinning is a special case of crystallographic twinning where the lattices of twin (different) domains (in a single crystal) overlap in three dimensions. An effect is superimposable lattices when the rotational symmetry of the lattice exceeds the rotational symmetry of the space group.

In this image, the crystal's unit cells are shown (3D squares, dark edges) with their contents as 7's. The crystal on the left is composed of two domains that represent a single untwinned crystal. The crystal on the right illustrates a merohedral twin, with the top domain rotated 180 degrees (rotation shown by red arrow).

An animation is available upon request.

merohedral, twinning, hemihedral, crystallography, non-epitaxial, rotational, symmetry, point group, Laue, superimposable lattice