Difference between revisions of "Corresponding twins"
From Online Dictionary of Crystallography
AndreAuthier (talk | contribs) |
|||
| Line 1: | Line 1: | ||
<font color="blue">Macles correspondantes</font> (''Fr''). <Font color="black">Geminati corrispondenti</Font> (''It'') | <font color="blue">Macles correspondantes</font> (''Fr''). <Font color="black">Geminati corrispondenti</Font> (''It'') | ||
| + | == Defonition == | ||
In case of [[twinning by merohedry]], when the [[twin element]] is twofold and the crystal is centrosymmetric, the [[twin operation]] can be described either as a rotation or as a reflection (the two operations being equivalent under the action of the center). | In case of [[twinning by merohedry]], when the [[twin element]] is twofold and the crystal is centrosymmetric, the [[twin operation]] can be described either as a rotation or as a reflection (the two operations being equivalent under the action of the center). | ||
| Line 7: | Line 8: | ||
Pairs of corresponding twins normally do not have the same frequency of occurrence, as one would be tempted to assume from the identical value of their [[twin obliquity]]. | Pairs of corresponding twins normally do not have the same frequency of occurrence, as one would be tempted to assume from the identical value of their [[twin obliquity]]. | ||
| + | |||
| + | == History == | ||
[[Category:Fundamental crystallography]] | [[Category:Fundamental crystallography]] | ||
Revision as of 14:19, 26 April 2006
Macles correspondantes (Fr). Geminati corrispondenti (It)
Defonition
In case of twinning by merohedry, when the twin element is twofold and the crystal is centrosymmetric, the twin operation can be described either as a rotation or as a reflection (the two operations being equivalent under the action of the center).
In case of twinning by pseudomerohedry, instead, the two twin operations are no longer equivalent even in centrosymmetric crystals but produce different twins, which are called reciprocal twins (Mügge, 1898) or corresponding twins (Friedel, 1904, 1926). One of the most classical examples is that of albite vs. pericline twins in feldspars.
Pairs of corresponding twins normally do not have the same frequency of occurrence, as one would be tempted to assume from the identical value of their twin obliquity.