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Twinning: Difference between revisions
→Twinning by Merohedry
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In a merohedral twin, the twin law is a symmetry operator of the crystal system, but not of the point group of the crystal. This means that the reciprocal lattices of the different twin domains superimpose exactly and the twinning is not directly detectable from the reflection pattern. This type is possible in the trigonal, tetragonal, hexagonal and cubic crystal systems, which have more than one Laue group. The twin law corresponds to the two-fold operation that is present in the apparent Laue group, but not in the true space group. Only for trigonal crystals is there more than one possible twin law. | In a merohedral twin, the twin law is a symmetry operator of the crystal system, but not of the point group of the crystal. This means that the reciprocal lattices of the different twin domains superimpose exactly and the twinning is not directly detectable from the reflection pattern. This type is possible in the trigonal, tetragonal, hexagonal and cubic crystal systems, which have more than one Laue group. The twin law corresponds to the two-fold operation that is present in the apparent Laue group, but not in the true space group. Only for trigonal crystals is there more than one possible twin law. | ||
Higher forms of twinning exist: tetartohedry (4 twin domains) and ogdohedry (8 twin domains). | |||
=== Twinning by Pseudo-Merohedry === | === Twinning by Pseudo-Merohedry === | ||