# Difference between revisions of "Mallard's law"

### From Online Dictionary of Crystallography

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The '''law of Mallard''' was introduced by Georges Friedel [''Leçons de Cristallographie'' (1926), p. 436] to explain, on a reticular basis, [[twinning by pseudomerohedry]]. | The '''law of Mallard''' was introduced by Georges Friedel [''Leçons de Cristallographie'' (1926), p. 436] to explain, on a reticular basis, [[twinning by pseudomerohedry]]. | ||

− | The law of Mallard states that [[twin element]]s are always rational (''i.e.'' [[direct lattice]] elements); therefore, a [[twin element|twin plane]] is a lattice plane, and a [[twin element|twin axis]] is a lattice row. These twin elements are pseudo[[symmetry element]]s for the lattice of the individual. The twin operations produce now slightly different orientations of the lattice of the individual, which are only quasi-equivalent, and no longer equivalent, as in the case of [[twinning by merohedry]]. | + | The law of Mallard states that [[twin element]]s are always rational (''i.e.'' [[direct lattice]] elements); therefore, a [[twin element|twin plane]] is a lattice plane, and a [[twin element|twin axis]] is a lattice row. These twin elements are pseudo-[[symmetry element]]s for the lattice of the individual. The twin operations produce now slightly different orientations of the lattice of the individual, which are only quasi-equivalent, and no longer equivalent, as in the case of [[twinning by merohedry]]. |

[[Category:Twinning]] | [[Category:Twinning]] |

## Latest revision as of 16:44, 20 December 2017

Loi de Mallard (*Fr*). Mallard-Gesetz (*Ge*). Legge di Mallard (*It*). マラード法則 (*Ja*). Ley de Mallard (*Sp*).

The **law of Mallard** was introduced by Georges Friedel [*Leçons de Cristallographie* (1926), p. 436] to explain, on a reticular basis, twinning by pseudomerohedry.

The law of Mallard states that twin elements are always rational (*i.e.* direct lattice elements); therefore, a twin plane is a lattice plane, and a twin axis is a lattice row. These twin elements are pseudo-symmetry elements for the lattice of the individual. The twin operations produce now slightly different orientations of the lattice of the individual, which are only quasi-equivalent, and no longer equivalent, as in the case of twinning by merohedry.