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 5:59 pm

All times are UTC - 4 hours




Post new topic Reply to topic  [ 11 posts ] 
Author Message
 Post subject: Chrome tourmaline, Usambara effect
PostPosted: Sat Jul 09, 2016 9:09 am 
Offline
Active Member

Joined: Fri Jun 08, 2012 11:33 am
Posts: 75
Chrome-tourmaline displaying the Usambara effect. The parent photo is the reference without the Usambara effect, therefore, to see the color change you should navigate through the children photos.
From Merelani Hills, Tanzania.
Enjoy! :D

Image
http://www.mindat.org/photo-728952.html


Top
 Profile  
Reply with quote  
 Post subject: Re: Chrome tourmaline, Usambara effect
PostPosted: Sat Jul 09, 2016 10:13 am 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 21602
Location: San Francisco
I'm not finding the Children's Photos, Daniel. Do you have a link?

Also one of my favorite Usambara articles is this one by Elise Skalwold:
http://www.nordskip.com/usambara.html


Top
 Profile  
Reply with quote  
 Post subject: Re: Chrome tourmaline, Usambara effect
PostPosted: Sat Jul 09, 2016 10:40 am 
Offline
Active Member

Joined: Fri Jun 08, 2012 11:33 am
Posts: 75
Barbra Voltaire wrote:
I'm not finding the Children's Photos, Daniel. Do you have a link?

Also one of my favorite Usambara articles is this one by Elise Skalwold:
http://www.nordskip.com/usambara.html


Hi Barbra,

That's why I am posting a link and not a picture so that everybody can find children photos there navigating with the arrows at the right (or left) of the photo in the link.

Here is the link for the child photo:
http://www.mindat.org/photo-728953.html

And I add more photos below
Image


Top
 Profile  
Reply with quote  
 Post subject: Re: Chrome tourmaline, Usambara effect
PostPosted: Sat Jul 09, 2016 12:24 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 21602
Location: San Francisco
Thanks!
Those photos are awesome!

I'm leaving your direct links now, as well as copying the picture to our site.


Top
 Profile  
Reply with quote  
 Post subject: Re: Chrome tourmaline, Usambara effect
PostPosted: Sat Jul 09, 2016 12:49 pm 
Offline
Active Member

Joined: Fri Jun 08, 2012 11:33 am
Posts: 75
Thank you, Barbra. I am very glad.


Top
 Profile  
Reply with quote  
 Post subject: Re: Chrome tourmaline, Usambara effect
PostPosted: Sat Jul 09, 2016 1:47 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 21602
Location: San Francisco
Thank YOU Dan. I am very glad you are participating more. :D


Top
 Profile  
Reply with quote  
 Post subject: Re: Chrome tourmaline, Usambara effect
PostPosted: Sat Jul 09, 2016 3:22 pm 
Offline
Gemology Online Veteran
User avatar

Joined: Mon Jun 16, 2014 1:10 pm
Posts: 850
Great pics!

I would love to hear what Bruce Fry knows about the Usambara effect in tourmaline.

_________________
http://www.gemstore-24.com/
gemstones, precision cuts and more...


Top
 Profile  
Reply with quote  
 Post subject: Re: Chrome tourmaline, Usambara effect
PostPosted: Sat Jul 09, 2016 3:34 pm 
Offline
Active Member

Joined: Fri Jun 08, 2012 11:33 am
Posts: 75
Thank you, Marlow.
I noticed that my link to the child photo doesn't work, therefore, for those who failed to open it I add here its picture (which is the most astounding of all).
Image


Top
 Profile  
Reply with quote  
 Post subject: Re: Chrome tourmaline, Usambara effect
PostPosted: Thu Aug 11, 2016 9:27 pm 
Offline
Gemology Online Veteran

Joined: Thu Sep 25, 2008 10:33 am
Posts: 840
Location: Mars PA
Unsambara effect is very interesting and I am not surprised that it is displayed by the most interesting of gemstones, Tourmaline. It is displayed by substances that absorb different wavelengths of visible light at different rates. Therefore if you had equal levels of say red and green in your light source at the start, they would not be equal after passing threw a substance demonstrating the unsambara effect. The tourmaline is demonstrating the effect all the time. but only in pieces that are thick enough, can the eye pick up the spectral change that results in the gemstone transmitting green to red light. You can see in the picture that there are areas of yellowish color that comes from having the right thickness to mix both red and green together to make yellow.

My first moment with the effect was when I put my spectrometer's light to the table of a small emerald cut with a spinach green color. I had not bought the gem as a unsambara tourmaline, but the red flashes that came out of the green tourmaline told me something was different. I love differences. Later I was able to find a collector with a similar tourmaline. Both were too small to let the eye see the color change (This is not a color change in the way it is generally accepted in the trade.), but when we placed them table to table and transmitted light threw them, they became red in their thicker parts and remained green at their edges.

A classic experiment with the effect is done with chlorophyll in water. You demonstrate the effect by pouring the liquid into a glass and when it gets to be deep enough, the color of transmitted light changes. I don't know of any other gemstone that demonstrates the effect nor do I expect a great demand for tourmaline that displays the effect, since most examples I have seen are dark and not that attractive in everyday light. You have to set out to appreciate the effect in my opinion, just like real color change takes some effort to see.

Bruce


Top
 Profile  
Reply with quote  
 Post subject: Re: Chrome tourmaline, Usambara effect
PostPosted: Thu Aug 11, 2016 9:44 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 4015
Location: North Carolina
Time for my favorite picture whenever this comes up: pumpkinseed oil.
Image
Of course, the most common example (so common it's boring and mundane) is orange or orange-red materials appearing yellow or amber in thin slivers.

_________________
Rough and cut classic and exotic synthetic gems:https://store.turtleshoard.com


Top
 Profile  
Reply with quote  
 Post subject: Re: Chrome tourmaline, Usambara effect
PostPosted: Fri Aug 12, 2016 12:39 am 
Offline
Gemology Online Veteran
User avatar

Joined: Mon Jun 16, 2014 1:10 pm
Posts: 850
Thank you, Stephen for the picture and Bruce for ( as usual ) very interesting informations.

A german gem and mineral desler in Germany ( Mawingu ) offers thin slices of extremely dark green tourmaline - with backlight and two slices you see it too.

But Danco item is much lighter and better.

I have another gem with an usambara effect - a chrysoberyl with a very high chrome content - so purplish red in daylight.

On a cloudy day if you look through the pavillion the thinner edges and half of the stone ( a twin ) are bluishgreen. If you turn it the stone is dark purplish red.

This is about synthetic alexandrite...

http://www.gia.edu/gems-gemology/spring ... e-sundberg



What about CC Garnets??

_________________
http://www.gemstore-24.com/
gemstones, precision cuts and more...


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 11 posts ] 

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 13 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:  
cron
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock