Talk:Crystal system

message: 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)
replies: text: For example, we don't appear to have consistent names for the seven crystal systems. The two different tables in this article use different names. --Dan|(talk) 10:43, 31 January 2006 (UTC)

text: Yes, the whole area of crystallography is in shambles... although I think space group is ok now. Would you be interested in starting work on for example point group or crystallographic point group along with me ane any others who are interested? Lots of other articles need work as well... O. Prytz 16:06, 6 February 2006 (UTC)

text: I just wish I had the time! I am hapy to add things here and there as I can, but we prolly need a 'plan of action' so we can all work to the same tune... --Dan|(talk) 23:25, 22 February 2006 (UTC)
thread_title:  Overhaul needed 

message: 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)
replies: text: This confusion between rhombohedral and trigonal is well established in the English wikipedia. Virtually all trigonal minerals are said to be in the "rhombohedral crystal system". It would be a big job to correct the articles on crystal systems, and all the current links.Judge Nutmeg 01:40, 23 May 2007 (UTC)
replies: text: A big job, sure, but it must be done! --Mahlerite 11:48, 23 May 2007 (UTC)
replies: text: Perhaps another point of confusion is that Lattice system redirects to Crystal system; the first sentence (In crystallography, a crystal system or crystal family or lattice system...) seeming to state that they are equivalent, the remainder of the paragraph attempting to explain the differences between these confused terms.Tomásdearg92 (talk) 12:21, 13 November 2010 (UTC)
thread_title:  Crystal system vs. lattice system 

message: 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)
thread_title:  WikiProject class rating

message: 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)
replies: text: Are you sure? Alpha, beta, zeta, What does it matter? The angles do not define the crystal system anyway, it is the symmetry constraints on the cell that do that. A good reference is  Glazer's "Space groups for Solid State scientists". I think on about pg 15, this is covered in quite some detail. User A1 (talk) 08:57, 21 April 2010 (UTC)
replies: text: This is about conventions, not science. Anyway, as I understand, alpha and beta (and thus lattice constants a, b) are interchangeable, but c is traditionally the largest lattice constant (and thus gamma is also selected angle), thus I don't see a problem with interchanged alpha and beta. Materialscientist (talk) 09:04, 21 April 2010 (UTC)
thread_title:  Monoclinic Wrongly Defined 

message: : Diamond crystal structure consists of face-centered cubic lattice.
How long has the caption said that? It's not precisely accurate, I believe. —Tamfang (talk) 07:57, 17 June 2011 (UTC)
replies: text: looks like it should point to Diamond cubic but clarifying the text is beyond me EdwardLane (talk) 14:37, 22 February 2012 (UTC)

text: I edited the text, it seems more precise now. Nicola.Manini (talk) 07:36, 29 February 2012 (UTC)
thread_title:  diamond 

message: 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)
thread_title:  RAD52 

message: 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)
replies: text: I like definition from "International Tables for Crystallography", vol A, page 804: "A direction is called polar if its two directional senses are geometrically or physically different. A polar symmetry direction of a crystal is called a polar axis." Also I substituted 'lattice' to 'structure'. Lattice always possess inversion center. Bor75 (talk) 23:01, 3 April 2013 (UTC)

text: Nicola.Manini, I created a new article Polar point group, which provides a geometric, rather than a chemical definition.  Wikfr (talk) 02:25, 10 December 2013 (UTC)

text: Bor75, thank you! I added appropriate hyperlinks from the present Crystal system page. Nicola.Manini (talk) 00:57, 18 December 2013 (UTC)
thread_title:  Polar? 

message: 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)
thread_title:  Symmetries of proteins 

message: 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)
thread_title:  I am not sure, but is this proper english? 

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thread_title:  External links modified 

message: 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)
thread_title:  2D confusion