Twin law

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Loi de macle (Fr). Legge di geminazione (It)

Twin law

The twin law expresses the operation that generates a twin. It is indicated by the symbol of the twin element of symmetry:  \bar 1, [uvw] and (hkl) for the centre of symmetry (inversion twin), direction of the rotation axis (rotation twin) and Miller indices of the mirror plane (reflection twin), in the order. Except when one refers to a specific plane or direction, the symbols {hkl} or <uvw> must be used to indicate all the planes or directions which are equivalent for symmetry.

Chapter 3.3 of International Tables of Crystallography, Volume D