CIBJO releases Gemmological Special Report: considers process of separating measurable facts from opinion; See Gemological Articles below.
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Mon Nov 11, 2019 11:21 pm

All times are UTC - 4 hours




Post new topic Reply to topic  [ 5 posts ] 
Author Message
 Post subject: rhombohedral and trigonal
PostPosted: Sun Nov 13, 2005 10:42 am 
Offline
Platinum Member

Joined: Sun Oct 16, 2005 12:42 pm
Posts: 2591
Yesterday in chat we were asked to clear an issue concerning the trigonal crystal system.
There was some confusion about books interchanging rhombohedral and trigonal.

As it was 2AM I wasn't very keen on grabbing my own books to provide an answer, so here it is.

The rhombohedral and trigonal crystal systems are the same, so the names are interchangable.
There is a huge difference in habit though (or I should say in unit cell).
What they have in common is the symmetry and that is why they fall in the same trigonal group (or rhombohedral group if you wish).

Some unit cells are rhombohedrons while other unit cells are what we traditonaly see as trigonal.
Have a look at http://www.uwgb.edu/dutchs/symmetry/trigrhuc.htm

In the first 3 images you see that the prisms are made up of tiny trigonals. The 2 images below are made up of tiny rhombohedrons.

Scroll down a bit more to see the scalenohedron and it will be more obvious (below that is a blown up rhombohedron).

Also take a look at http://jcrystal.com/steffenweber/POLYHEDRA/p_24.html
There you will see an interactive rhombohedron (use your mouse). It will be very hard to see the trigonal and digonal axes of symmetry, but they are there.

Nice to learn new things.


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Sun Nov 13, 2005 11:50 am 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 3:36 pm
Posts: 195
Location: San Francisco
As usual doos, excellent information.
Would it be possible for me to make a reference page of ALL your previous chats? I think the information you and Annie have provided would be tremendously valuable to others.
I recall you had a list posted at some time, but I lost it when I had to reinstall my operating system :cry: .

_________________
"Do well and you will have no need for ancestors" Voltaire


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Sun Nov 13, 2005 6:16 pm 
WOW Anatase! Great job on the new link: http://gemologyonline.com/chat_index.html


Top
  
Reply with quote  
 Post subject:
PostPosted: Sat Nov 19, 2005 8:44 pm 
Offline
Established Member

Joined: Sun Oct 16, 2005 1:45 pm
Posts: 11
Thanks Doos,

You keep coming up with the answers to the hard questions. I've bookmarked both of these sites they look outstanding but they'll have to be explored later as it's almost 2am....THANKS

Yours aye

Frank

PS yes your right I should have paid more attention to the chat instead of searching out this post...I'm suitably chagrined :( chats finished now...can I post?

:P


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Mon Nov 21, 2005 5:21 pm 
Offline
Platinum Member

Joined: Sun Oct 16, 2005 12:42 pm
Posts: 2591
I was just bitching, nothing personal. Just one of my hobbies.


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 posts ] 

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock