January 24 Through February 4—TUCSON, ARIZONA: Annual show
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Thu Mar 28, 2024 12:10 pm

All times are UTC - 4 hours




Post new topic Reply to topic  [ 5 posts ] 
Author Message
 Post subject: Identifying rough gems
PostPosted: Sat Feb 07, 2009 8:23 am 
Offline
New to the Forum or The Quiet Type

Joined: Tue Jan 08, 2008 8:42 am
Posts: 2
Location: South Africa
Hi there everyone

I really battle with identifying rough gems as I can't seem to grasp the idea of crystal systems and habit, no matter how many times I read my FGA notes, various gem books and online articles on the subject. I understand the laws of the crystal systems but I can't seem to "see" the crystal system in a gem. Are there any guidelines to working it out or is it just something that needs lots of practice?

I'd really appreciate any help as this is a pretty big problem for someone studying gem identification!!

Many thanks
Gem (- seriously!)


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Sat Feb 07, 2009 10:11 am 
Offline
Valued Contributor
User avatar

Joined: Wed Oct 22, 2008 1:48 am
Posts: 120
Location: Germany
Well, sometimes you do have to look very carefully at a rough gem to find some of it's original crystal surfaces to identify. And sometimes, there just isn't any of the original crystal surface left to see.

For example, you would not be able to identify this piece of garnet rough based on crystal shape, because none of the original crystal shape remains. (However, the conchoidal fracture is one clue that this is in fact garnet... but glass also has conchoidal fracture, so you have to be careful!)
Image

These garnets are easy to identify based on their characteristic crystal habit:
Image

One caveat though - there are people who will carefully machine gems to look like other types of mineral crystals... a classic recent example is phenakite that was machined to look like diamond crystals! (Click on the image to go to Thomas Hainschwang's full report.)
Image

The lesson - use a preponderance of evidence to help you figure out what minerals you have! :)

You might try looking at some mineralogy books for more help with learning how to ID gems using crystal systems, fracture, hardness, etc. Mineralogy relies heavily on these characteristics for identifying minerals in rocks.


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Sat Feb 07, 2009 1:58 pm 
Offline
Platinum Member

Joined: Tue Jun 03, 2008 4:40 pm
Posts: 2667
Location: South Dakota
I find it rather confusing sometimes too. Let's not forget mineral epimorphs, pseudomorphs, multiple crystal systems and habits for the same mineral.....

_________________
MrAmethystguy ~ Some jokes just fluorite over my head!


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Sat Feb 07, 2009 2:38 pm 
Offline
Platinum Member

Joined: Sun Oct 16, 2005 12:42 pm
Posts: 2591
Hi,

Think of the different forms that make a "habit" as lego tiles (the "forms") with which you can make different shapes (the habit).

Image

With a lot of cubes you can build 2 pyramids (as they did in Egypt), glue them together at the base and you have an octahedron .. one of the shapes (or better "habits") of the cubic system.

Hope that helped a bit.

_________________
Proud to be a DSN and JTV shopper, just love the guys!


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Tue Feb 10, 2009 12:21 pm 
Offline
New to the Forum or The Quiet Type

Joined: Tue Jan 08, 2008 8:42 am
Posts: 2
Location: South Africa
Hi there

Thank you all so very much for your help. I guess not putting so much emphasis on the crystal system is what I can take away from this.

Thanks especially to Doos, I didn't think I'd ever understand habit and form so clearly!! They make so much sense now.


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 17 guests


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