Merohedral - Revision history

MassimoNespolo: lang (Fr, It)

2018-11-30T14:50:59Z

lang (Fr, It)

MassimoNespolo: statement contradicted by the discussion just below it

2018-11-30T14:49:13Z

statement contradicted by the discussion just below it

BrianMcMahon: Added German and Spanish translations (U. Mueller)

2017-11-16T12:41:12Z

Added German and Spanish translations (U. Mueller)

BrianMcMahon at 16:27, 15 May 2017

2017-05-15T16:27:06Z

BrianMcMahon: Style edits to align with printed edition

2017-05-15T16:26:48Z

Style edits to align with printed edition

MassimoNespolo: typo (4, not two!)

2016-12-20T12:09:33Z

typo (4, not two!)

MassimoNespolo: typo (missing space)

2016-10-13T11:13:11Z

typo (missing space)

MassimoNespolo at 11:22, 25 January 2009

2009-01-25T11:22:09Z

New page

'''Merohedral''' is the adjectival form of [[merohedry]] and indicates a crystal that does not possess the full point symmetry of its lattice.

==Discussion==
In the literature, the term ''merohedral twinning'' is often improperly used instead of [[twinning by merohedry]]. A merohedral crystal may undergo several different types of twinning and for this reason the term "merohedral twinning" is misleading, as the following example shows.

A crystal belonging to the [[geometric crystal class]] 2 is merohedral because its lattice has at least symmetry 2/''m''. There are thee supergroups of order two of the point group 2 which correspond to three different twins.
#Twinning by reflection across the (010) plane or by inversion: this corresponds to [[twinning by merohedry]], twin point group 2/''m''';
#Twinning by reflection across the (100) or (001) plane: this corresponds to [[twinning by pseudomerohedry]], [[twinning by reticular merohedry]], or [[twinning by reticular pseudomerohedry]] if β ≠ 90º, or to [[twinning by metric merohedry]] if β = 90º; the twin point group is ''m'' ′ 2 ''m'' ′
#Twinning by rotation about [100] or [001]: direction: this corresponds tothe same types of twinning as case 2) above but the twin point group is 2′ 2 2′.
Case 1 above would be a "merohedral twin of a merohedral crystal" while cases 2 and 3 would be "non-merohedral twins of a merohedral crystal".
To avoid any terminological awkwardness, the adjective '''merohedric''' has been suggested with reference to twins, but the use of the category names like [[twinning by merohedry]] remains preferable

==See also==
*[[Merohedry]]
*[[Twinning]]

[[Category:Fundamental crystallography]]
[[Category:Twinning]]

← Older revision		Revision as of 14:50, 30 November 2018
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−	<font color="red">Meroedrisch</font> (''Ge''). <font color="green">Meroédrico</font> (''Sp'').	+	<font color="blue">Mérièdre</font> (''Fe''). <font color="red">Meroedrisch</font> (''Ge''). <font color="black">Meroedrico</font> (''It''). <font color="green">Meroédrico</font> (''Sp'').
		+

	'''Merohedral''' is the adjectival form of [[merohedry]] and indicates a crystal that does not possess the full point symmetry of its lattice.		'''Merohedral''' is the adjectival form of [[merohedry]] and indicates a crystal that does not possess the full point symmetry of its lattice.

@@ Line 1: / Line 1: @@
 <font color="red">Meroedrisch</font> (''Ge''). <font color="green">Meroédrico</font> (''Sp'').
-'''Merohedral''' is the adjectival form of [[merohedry]] and indicates a crystal that does not possess the full point symmetry of its lattice. Merohedral twins are the result of [[Twinning|twinning]] by merohedry.
+'''Merohedral''' is the adjectival form of [[merohedry]] and indicates a crystal that does not possess the full point symmetry of its lattice.
 ==Discussion==

← Older revision		Revision as of 12:41, 16 November 2017
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		+	<font color="red">Meroedrisch</font> (''Ge''). <font color="green">Meroédrico</font> (''Sp'').
		+
	'''Merohedral''' is the adjectival form of [[merohedry]] and indicates a crystal that does not possess the full point symmetry of its lattice. Merohedral twins are the result of [[Twinning\|twinning]] by merohedry.		'''Merohedral''' is the adjectival form of [[merohedry]] and indicates a crystal that does not possess the full point symmetry of its lattice. Merohedral twins are the result of [[Twinning\|twinning]] by merohedry.

@@ Line 9: / Line 9: @@
 #Twinning by rotation about the [100] or [001] direction: this corresponds to the same types of twinning as case 2 above but the twin point group is 2&prime;22&prime;.
 Case 1 above would be a 'merohedral twin of a merohedral crystal' while cases 2 and 3 would be 'non-merohedral twins of a merohedral crystal'.
 To avoid any terminological awkwardness, the adjective '''merohedric''' has been suggested with reference to twins, but the use of the category names like [[twinning by merohedry]] remains preferable.

@@ Line 1: / Line 1: @@
-'''Merohedral''' is the adjectival form of [[merohedry]] and indicates a crystal that does not possess the full point symmetry of its lattice.
+'''Merohedral''' is the adjectival form of [[merohedry]] and indicates a crystal that does not possess the full point symmetry of its lattice. Merohedral twins are the result of [[Twinning|twinning]] by merohedry.
 ==Discussion==
-In the literature, the term ''merohedral twinning'' is often improperly used instead of [[twinning by merohedry]]. A merohedral crystal may undergo several different types of twinning and for this reason the term "merohedral twinning" is misleading, as the following example shows.
+In the literature, the term ''merohedral twinning'' is often improperly used instead of [[twinning by merohedry]]. A merohedral crystal may undergo several different types of twinning and for this reason the term 'merohedral twinning' is misleading, as the following example shows.
-A crystal belonging to the [[geometric crystal class]] 2 is merohedral because its lattice has at least symmetry 2/''m''. There are thee minimal supergroups of order four of the point group 2 which correspond to three different twins.
+A crystal belonging to the [[geometric crystal class]] 2 is merohedral because its lattice has at least symmetry 2/''m''. There are three minimal supergroups of order four of the point group 2 which correspond to three different twins.
-#Twinning by reflection across the (010) plane or by inversion: this corresponds to [[twinning by merohedry]], twin point group 2/''m''';
+#Twinning by reflection across the (010) plane or by inversion: this corresponds to [[twinning by merohedry]], twin point group 2/''m'''.
-#Twinning by reflection across the (100) or (001) plane: this corresponds to [[twinning by pseudomerohedry]], [[twinning by reticular merohedry]], or [[twinning by reticular pseudomerohedry]] if &beta; &ne; 90º, or to [[twinning by metric merohedry]] if &beta; = 90º; the twin point group is ''m'' &prime; 2 ''m'' &prime;
+#Twinning by reflection across the (100) or (001) plane: this corresponds to [[twinning by pseudomerohedry]], [[twinning by reticular merohedry]], or [[twinning by reticular pseudomerohedry]] if &beta; &ne; 90º, or to [[twinning by metric merohedry]] if &beta; = 90º; the twin point group is ''m''&prime;2''m''&prime;.
-#Twinning by rotation about [100] or [001]: direction: this corresponds to the same types of twinning as case 2) above but the twin point group is 2&prime; 2 2&prime;.
+#Twinning by rotation about the [100] or [001] direction: this corresponds to the same types of twinning as case 2 above but the twin point group is 2&prime;22&prime;.
-Case 1 above would be a "merohedral twin of a merohedral crystal" while cases 2 and 3 would be "non-merohedral twins of a merohedral crystal".
+Case 1 above would be a 'merohedral twin of a merohedral crystal' while cases 2 and 3 would be 'non-merohedral twins of a merohedral crystal'.
-To avoid any terminological awkwardness, the adjective '''merohedric''' has been suggested with reference to twins, but the use of the category names like [[twinning by merohedry]] remains preferable
+To avoid any terminological awkwardness, the adjective '''merohedric''' has been suggested with reference to twins, but the use of the category names like [[twinning by merohedry]] remains preferable.
 ==See also==