# Difference between revisions of "Twinning (effects of)"

### From Online Dictionary of Crystallography

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<Font color="blue"> Maclage (effets de) </Font>(''Fr'') <Font color="black"> Geminazione (effetti della) </Font>(''It'') | <Font color="blue"> Maclage (effets de) </Font>(''Fr'') <Font color="black"> Geminazione (effetti della) </Font>(''It'') | ||

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+ | = Morphological and optical effects = | ||

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+ | At morphological level, twinning introduces re-entrant angles that, in principle, are specific marks. | ||

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+ | Except for twins by merohedry, the orientation of the optical indicatrix changes through the inteface between adjacent crystals (individuals). Thus, a part particular orientations, if observed by a polarizing microscope between crossed polars, a twin never can be brought by rotation at a position of complete extinctions (dark field). | ||

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= Overlap of lattices = | = Overlap of lattices = | ||

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By effect of a ''[[twinning operation]]'', both the direct and reciprocal lattice of the individuals forming a [[twin]] are overlapped. Overlapping (restoration) of nodes belonging to different individuals can be: (i) exact and total ([[twinning by merohedry]]); (ii) exact but partial (i.e. only a fraction of the nodes of an individual lattice is restored; [[twinning by reticular merohedry]]); (iii) total but approximate ([[twinning by pseudomerohedry]]), approximate and partial ([[twinning by reticular pseudomerohedry]]). | By effect of a ''[[twinning operation]]'', both the direct and reciprocal lattice of the individuals forming a [[twin]] are overlapped. Overlapping (restoration) of nodes belonging to different individuals can be: (i) exact and total ([[twinning by merohedry]]); (ii) exact but partial (i.e. only a fraction of the nodes of an individual lattice is restored; [[twinning by reticular merohedry]]); (iii) total but approximate ([[twinning by pseudomerohedry]]), approximate and partial ([[twinning by reticular pseudomerohedry]]). | ||

[[Twin lattice]], [[twin index]] and [[twin obliquity]] are entries related to the overlap of lattices. | [[Twin lattice]], [[twin index]] and [[twin obliquity]] are entries related to the overlap of lattices. | ||

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+ | For effects of twinning on a diffraction pattern see [[twinning (diffraction pattern of)]]. | ||

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

## Revision as of 13:59, 16 May 2006

Maclage (effets de) (*Fr*) Geminazione (effetti della) (*It*)

# Morphological and optical effects

At morphological level, twinning introduces re-entrant angles that, in principle, are specific marks.

Except for twins by merohedry, the orientation of the optical indicatrix changes through the inteface between adjacent crystals (individuals). Thus, a part particular orientations, if observed by a polarizing microscope between crossed polars, a twin never can be brought by rotation at a position of complete extinctions (dark field).

# Overlap of lattices

By effect of a *twinning operation*, both the direct and reciprocal lattice of the individuals forming a twin are overlapped. Overlapping (restoration) of nodes belonging to different individuals can be: (i) exact and total (twinning by merohedry); (ii) exact but partial (i.e. only a fraction of the nodes of an individual lattice is restored; twinning by reticular merohedry); (iii) total but approximate (twinning by pseudomerohedry), approximate and partial (twinning by reticular pseudomerohedry).
Twin lattice, twin index and twin obliquity are entries related to the overlap of lattices.

For effects of twinning on a diffraction pattern see twinning (diffraction pattern of).