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, page 436) to explain, or reticular bases, [[twinning by pseudomerohedry]]. | The '''law of Mallard''' was introduced by Georges Friedel (Leçons de Cristallographie 1926, page 436) to explain, or reticular bases, [[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 pseudosymmetry elements for the lattice of the individual. The twin operations produce now sligthly 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 elements 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 pseudosymmetry elements for the lattice of the individual. The twin operations produce now sligthly 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:Fundamental crystallography]] | [[Category:Fundamental crystallography]] | ||
Revision as of 11:50, 15 May 2006
Loi de Mallard(Fr). Legge di Mallard (It)
The law of Mallard was introduced by Georges Friedel (Leçons de Cristallographie 1926, page 436) to explain, or reticular bases, 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 pseudosymmetry elements for the lattice of the individual. The twin operations produce now sligthly 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.