Talk:Hermann–Mauguin notation

New article

This page used to redirect to Crystallographic point group, which mentions the Hermann-Mauguin notation but doesn't really explain it. So I created this article. It still needs a bit of work though, so i tagged it as a stub, although the attention tag may be more appropriate.O. Prytz 19:13, 7 June 2006 (UTC)

This page is pretty opaque. It doesn't describe all of the symbols in the notation. For example, the slash (/) and overbar (-) are not explained. I don't understand these or I'd add it myself. Giving the names of some of the point groups (e.g. dihedral group, etc.) and comparing to Schoenflies notation in these cases would also be beneficial. 131.215.107.130 02:00, 1 March 2007 (UTC)

Listing of possible screw axis notations seems to miss 3₂. It is essential and different from 3₁, since it distinguishes right and left-hand screw directions. —Preceding unsigned comment added by 131.112.140.130 (talk) 08:19, 20 January 2011 (UTC)

Fraction formatting bad

These tall formula fractions make the article flow very elogated and less readable. Tom Ruen (talk) 05:48, 8 December 2011 (UTC)

I thought that for full symbols tall fractions looks better. One can see immediately, how many positions are in the symbol (axis and plane really take just one position in the symbol). At least, for me, ${\tfrac {4}{m}}$3${\tfrac {2}{m}}$ looks more clear, than 4/m 3 2/m. And ${\tfrac {4}{m}}{\tfrac {2}{m}}{\tfrac {2}{m}}$ — than 4/m 2/m 2/m.

I checked Internationl Tables and textbooks. IT uses both. Here http://it.iucr.org/Ab/ch10o1v0001/table10o1o2o4/ — tall fractions for full symbols; here http://it.iucr.org/Ab/ch12o1v0001/#table12o1o4o2 — "slash fractions" (I don't know, how to call them) for full symbols. Textbooks usually use tall fractions for full symbols, but some new also started to write in text something like 4/m 3 2/m (IMHO, looks ugly). I would prefer to leave tall formula fractions. Bor75 (talk) 05:09, 12 December 2011 (UTC)

The problem (maybe on my browser), is there's line breaks between symbols. This is vertical: (3 vertically stacked symbols)

${\tfrac {4}{m}}$3${\tfrac {2}{m}}$

I see a mathbf tag used that seems to help. Tom Ruen (talk) 06:21, 12 December 2011 (UTC) $\mathbf {\tfrac {4}{m}}$3$\mathbf {\tfrac {2}{m}}$ AND $\mathbf {{\tfrac {4}{m}}{\tfrac {2}{m}}{\tfrac {2}{m}}}$

In section Point Groups, 3rd paragraph, about which notation to use.

Hello, first time messing around with Wikipedia, please excuse any involuntary noncompliance with standard procedure here.

As I understood, 3/m generates a pattern with 6 points. 3 for the 3-fold rotation and 3 more for reflecting them. 6 also generates a pattern with 6 points. Both apply for a triangular prism e.g. with which I imagine the operations. So shouldn't it be right to use 3/m instead of 6 in this case? Since both generate 6 points and rotation axis is to be preferred if number of generated points is equal.

The article says n=3 generates 3 points. I'd say that's correct. Then it states, that 6 should be written instead of 3/m. With my understanding this is wrong.

I'd appreciate it very much if someone could clear things up, maybe I just misinterpreted something. Thank you.

WhosAGoodBoy (talk) 08:23, 28 April 2021 (UTC)

I think i understand now. Here the indicated reflection plane in 3/m does not add to the generated points (6/m is also only generating 6, not 12 points as indicated in the article). Therefore writing 6 instead of 3/m makes sense after all.

So it comes down to convention! In the german Wiki 3/m generates a pattern with 6 points (symmetry equivalent objects), 3 only generates a pattern with 3.

I conclude that the referenced paragraph is hard do understand without explaining the background of the used convention!

WhosAGoodBoy (talk) 08:49, 28 April 2021 (UTC)

Source [1]

In case anyone wants to check the source, I found a PDF of the book here:

https://www.geokniga.org/bookfiles/geokniga-introduction-crystallography.pdf

The quoted section is under section 3.5 page 54 Hence I will update the citation. from "p.165" to the above. ISBN of the linked book is the same to the the one under [1] in the article.

141.20.217.201 (talk) 19:36, 27 September 2021 (UTC)