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This article is rather chaotic and contains a lot of information that in my opinion belongs elsewhere. This article should in my opinion concentrate on describing the 7 crystal systems (cubic, tetragonal etc) and explaining the restrictions on the axial system (cubic: a=b=c, α=β=γ=90°, etc). A short explanation on the relationship with Bravais lattice should be given, but there should be a separate article for that subject (the two should not be merged as they are now). Info on crystallographic point groups should be covered in that article, and not here. This will result in a much shorter article, so I want to hear any comments first. If there are none, I'll implement the changes within a couple of days. O. Prytz 18:44, 8 January 2006 (UTC)
I agree. There are a lot of related pages, and they are somewhat chaotic too. We should try to consolidate all the different pieces of information into a set of concise pages. Also we need to implement the different focus of crystallographers, protein crystallographers and mathematicians. This is why I added the 'enantiomorphic' column to the table of point groups, as protein crystallographers are not interested in centrosymmetric point groups. -- Dan| (talk) 09:59, 31 January 2006 (UTC)
As in other wikipedias, this article badly mixes different notions, those of crystal system, lattice system and crystal family. I am mainly working on the French wikipedia, where I had a hard time trying putting a bit of order there. I don't have the time of doing the same here, but you can refer to the IUCr online dictionary of crystallography, see: Crystal system, Lattice system and Crystal family. In particular, rhombohedral and trigonal are not synonyms, the first is a lattice system, the second a crystal system. Mahlerite 17:25, 9 April 2007 (UTC)
This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 09:46, 10 November 2007 (UTC)
In all the pages that discuss monoclinic crystals (including Crystal system, Bravais lattice, Monoclinic crystal, etc.), the symmetry of the crystal is wrongly defined. For monoclinic crystals, all angles are 90 degrees, except for BETA (not alpha, as currently indicated). This requires editing all text and Figures depicting monoclinic crystals. Note that, for instance, this mistake does not exist in the french wikipedia http://fr.wikipedia.org/wiki/Monoclinique. Also, you can look at http://webmineral.com/crystal/Monoclinic-Prismatic.shtml to see that beta ≠ 90° is the standard. Wolf.aarons ( talk) 17:18, 20 April 2010 (UTC)
How long has the caption said that? It's not precisely accurate, I believe. — Tamfang ( talk) 07:57, 17 June 2011 (UTC)
This statement:
"For example the Rad52 DNA binding protein has an 11-fold rotational symmetry (in human), however, it must form crystals in one of the 11 enantiomorphic point groups given above."
is severely misleading
RAD52 is a 7-mer in solution (see the original publications of the structure) and therefore most likely also "(in human)" the undecameric configuration of RAD52 is considered to be an artifact of cleaving a major fraction of the c-terminal protein regions which was necessary in order to obtain crystals. RAD52 is a heptamer in analytical ultracentrifugation and shifts to undecamer when the c-terminus is cut off. The group that solved the structure mentioned that. Also, the EM structure of RAD52 is a heptamer with rotational and translational symmetry.
Kagawa W 2002, Mol.Cell, PMID:12191481 Stasiak AZ 2000, Curr, Biol., PMID:10744977
A better example would maybe be RecA which has a ~6.1 fold symmetry when bound to DNA but has to crystallize as perfect hexamer. All RecA crystal structures are in P6(1) and not in a configuration that allows for DNA binding. The RecA-DNA structure from Pavletich's lab was composed of fused protomers that crystallized as one building block in a tetragonal spacegroup. The fused protomers have an internal ~6.1 symmetry in the asymmetric unit cell, as they should.
Muckbacher ( talk) 01:16, 23 August 2012 (UTC)
After the table with Crystal Classes, an explanation is attempted of the "Point symmetry" classification.
It looks mostly fine except for the part "If rotation of the original lattice reveals an axis where the two ends are different, then the crystal is polar. H2O is a common example of a polar molecule." What does the polarity of a molecule have to to with the mathematical properties of Point symmetry of a crystal system? Also the link of polar in the table to the chemical polarity of molecules is at best misleading. In the present article "polar" should be a property of the crystal symmetry, with little or no connection with the chemical properties of whatever is composing the crystal. We need a satisfactory definition of "polar crystal symmetry" somewhere, possibly in this page or in a specific one.
Nicola.Manini ( talk) 16:57, 5 March 2013 (UTC)
I've tried to clarify the part about polar crystals. I'm a physicist: what is written now makes sense, and it is far better than what was there before. I'm not a crystallographer: there may be better ways to put it. The link of polar is still to be fixed, I still cannot tell where it should point to. Nicola.Manini ( talk) 11:45, 14 March 2013 (UTC)
I removed paragraph
The protein assemblies themselves may have symmetries other than those given above, because they are not intrinsically restricted by the Crystallographic restriction theorem. For example the Rad52 DNA binding protein has an 11-fold rotational symmetry (in human), however, it must form crystals in one of the 11 enantiomorphic point groups given above.
This information is not related to this article, it is better to mention about it in Crystal structure or Crystallographic point group, for example. Second, this information is related not only to "protein assemblies", but to any molecule. For example, Ferrocene possess 5-fold axis, but crystallizes in the monoclinic space group. Bor75 ( talk) 00:21, 4 April 2013 (UTC)
The section Crystal classes has a table with a column called Group structure, which I think is inconsistant or wrong. Dihedral and 2xdihedral seem to be used interchangably to mean groups of order 8, 12, and 24. I am also wondering why 2xcyclic is shown, instead of dihedral.
The notation seems non-standard. Does 2xdihedral mean the product of cycle group of order 2 and the dihedral group of unspecified order, or two copies of the dihedral group? What does 2xcyclic mean?
I would like to change the column heading from "Group structure" to "Abstract group".
Wikfr ( talk) 00:32, 14 November 2013 (UTC)
It's below the first table: Caution: No "trigonal" lattice system. To avoid confusion of terminology, not use the term "trigonal lattice"; or use the definition that "trigonal lattice"="hexagonal lattice"≠"rhombohedral lattice". — Preceding unsigned comment added by 2001:4CA0:4FFF:1:0:0:0:123 ( talk) 13:35, 8 May 2015 (UTC)
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In other dimensions, the first section briefly discussed 2D crystal structures:
"Two dimensional space has the same number of crystal systems, crystal families, and lattice systems. In 2D space, there are four crystal systems: oblique, rectangular, square, and hexagonal."
The first sentence originally reads as if there are the same number of crystal systems (and etc) as in the 3D space (7). The second sentence clarifying the four categories disputes this. I believe the first sentence is trying to say that there are four of each or rather systems=families=lattices all with the same four names. That makes sense given the limits of rotational symmetry in 2D, but I'm not confident in my understanding. If this is what was meant, could we rewrite the passage to make that clearer? I can make subtle adjustments like below, but I still think it needs something else.
"In 2D space, there are four crystal systems: oblique, rectangular, square, and hexagonal. Two dimensional space has an equal number of crystal systems, crystal families, and lattice systems." AniKitt ( talk) 22:33, 4 May 2024 (UTC)
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This article is rather chaotic and contains a lot of information that in my opinion belongs elsewhere. This article should in my opinion concentrate on describing the 7 crystal systems (cubic, tetragonal etc) and explaining the restrictions on the axial system (cubic: a=b=c, α=β=γ=90°, etc). A short explanation on the relationship with Bravais lattice should be given, but there should be a separate article for that subject (the two should not be merged as they are now). Info on crystallographic point groups should be covered in that article, and not here. This will result in a much shorter article, so I want to hear any comments first. If there are none, I'll implement the changes within a couple of days. O. Prytz 18:44, 8 January 2006 (UTC)
I agree. There are a lot of related pages, and they are somewhat chaotic too. We should try to consolidate all the different pieces of information into a set of concise pages. Also we need to implement the different focus of crystallographers, protein crystallographers and mathematicians. This is why I added the 'enantiomorphic' column to the table of point groups, as protein crystallographers are not interested in centrosymmetric point groups. -- Dan| (talk) 09:59, 31 January 2006 (UTC)
As in other wikipedias, this article badly mixes different notions, those of crystal system, lattice system and crystal family. I am mainly working on the French wikipedia, where I had a hard time trying putting a bit of order there. I don't have the time of doing the same here, but you can refer to the IUCr online dictionary of crystallography, see: Crystal system, Lattice system and Crystal family. In particular, rhombohedral and trigonal are not synonyms, the first is a lattice system, the second a crystal system. Mahlerite 17:25, 9 April 2007 (UTC)
This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 09:46, 10 November 2007 (UTC)
In all the pages that discuss monoclinic crystals (including Crystal system, Bravais lattice, Monoclinic crystal, etc.), the symmetry of the crystal is wrongly defined. For monoclinic crystals, all angles are 90 degrees, except for BETA (not alpha, as currently indicated). This requires editing all text and Figures depicting monoclinic crystals. Note that, for instance, this mistake does not exist in the french wikipedia http://fr.wikipedia.org/wiki/Monoclinique. Also, you can look at http://webmineral.com/crystal/Monoclinic-Prismatic.shtml to see that beta ≠ 90° is the standard. Wolf.aarons ( talk) 17:18, 20 April 2010 (UTC)
How long has the caption said that? It's not precisely accurate, I believe. — Tamfang ( talk) 07:57, 17 June 2011 (UTC)
This statement:
"For example the Rad52 DNA binding protein has an 11-fold rotational symmetry (in human), however, it must form crystals in one of the 11 enantiomorphic point groups given above."
is severely misleading
RAD52 is a 7-mer in solution (see the original publications of the structure) and therefore most likely also "(in human)" the undecameric configuration of RAD52 is considered to be an artifact of cleaving a major fraction of the c-terminal protein regions which was necessary in order to obtain crystals. RAD52 is a heptamer in analytical ultracentrifugation and shifts to undecamer when the c-terminus is cut off. The group that solved the structure mentioned that. Also, the EM structure of RAD52 is a heptamer with rotational and translational symmetry.
Kagawa W 2002, Mol.Cell, PMID:12191481 Stasiak AZ 2000, Curr, Biol., PMID:10744977
A better example would maybe be RecA which has a ~6.1 fold symmetry when bound to DNA but has to crystallize as perfect hexamer. All RecA crystal structures are in P6(1) and not in a configuration that allows for DNA binding. The RecA-DNA structure from Pavletich's lab was composed of fused protomers that crystallized as one building block in a tetragonal spacegroup. The fused protomers have an internal ~6.1 symmetry in the asymmetric unit cell, as they should.
Muckbacher ( talk) 01:16, 23 August 2012 (UTC)
After the table with Crystal Classes, an explanation is attempted of the "Point symmetry" classification.
It looks mostly fine except for the part "If rotation of the original lattice reveals an axis where the two ends are different, then the crystal is polar. H2O is a common example of a polar molecule." What does the polarity of a molecule have to to with the mathematical properties of Point symmetry of a crystal system? Also the link of polar in the table to the chemical polarity of molecules is at best misleading. In the present article "polar" should be a property of the crystal symmetry, with little or no connection with the chemical properties of whatever is composing the crystal. We need a satisfactory definition of "polar crystal symmetry" somewhere, possibly in this page or in a specific one.
Nicola.Manini ( talk) 16:57, 5 March 2013 (UTC)
I've tried to clarify the part about polar crystals. I'm a physicist: what is written now makes sense, and it is far better than what was there before. I'm not a crystallographer: there may be better ways to put it. The link of polar is still to be fixed, I still cannot tell where it should point to. Nicola.Manini ( talk) 11:45, 14 March 2013 (UTC)
I removed paragraph
The protein assemblies themselves may have symmetries other than those given above, because they are not intrinsically restricted by the Crystallographic restriction theorem. For example the Rad52 DNA binding protein has an 11-fold rotational symmetry (in human), however, it must form crystals in one of the 11 enantiomorphic point groups given above.
This information is not related to this article, it is better to mention about it in Crystal structure or Crystallographic point group, for example. Second, this information is related not only to "protein assemblies", but to any molecule. For example, Ferrocene possess 5-fold axis, but crystallizes in the monoclinic space group. Bor75 ( talk) 00:21, 4 April 2013 (UTC)
The section Crystal classes has a table with a column called Group structure, which I think is inconsistant or wrong. Dihedral and 2xdihedral seem to be used interchangably to mean groups of order 8, 12, and 24. I am also wondering why 2xcyclic is shown, instead of dihedral.
The notation seems non-standard. Does 2xdihedral mean the product of cycle group of order 2 and the dihedral group of unspecified order, or two copies of the dihedral group? What does 2xcyclic mean?
I would like to change the column heading from "Group structure" to "Abstract group".
Wikfr ( talk) 00:32, 14 November 2013 (UTC)
It's below the first table: Caution: No "trigonal" lattice system. To avoid confusion of terminology, not use the term "trigonal lattice"; or use the definition that "trigonal lattice"="hexagonal lattice"≠"rhombohedral lattice". — Preceding unsigned comment added by 2001:4CA0:4FFF:1:0:0:0:123 ( talk) 13:35, 8 May 2015 (UTC)
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I have just modified one external link on Crystal system. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
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In other dimensions, the first section briefly discussed 2D crystal structures:
"Two dimensional space has the same number of crystal systems, crystal families, and lattice systems. In 2D space, there are four crystal systems: oblique, rectangular, square, and hexagonal."
The first sentence originally reads as if there are the same number of crystal systems (and etc) as in the 3D space (7). The second sentence clarifying the four categories disputes this. I believe the first sentence is trying to say that there are four of each or rather systems=families=lattices all with the same four names. That makes sense given the limits of rotational symmetry in 2D, but I'm not confident in my understanding. If this is what was meant, could we rewrite the passage to make that clearer? I can make subtle adjustments like below, but I still think it needs something else.
"In 2D space, there are four crystal systems: oblique, rectangular, square, and hexagonal. Two dimensional space has an equal number of crystal systems, crystal families, and lattice systems." AniKitt ( talk) 22:33, 4 May 2024 (UTC)