Photoluminescence Spectra of Emeralds from Colombia, Afghanistan, and Zambia by Brian Thompson. See Research Below
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Fri Nov 24, 2017 5:14 am

All times are UTC - 4 hours




Post new topic Reply to topic  [ 8 posts ] 
Author Message
 Post subject: Calling a purplish red tourmalinle, cuprian
PostPosted: Mon Mar 13, 2017 9:24 pm 
Offline
Gemology Online Veteran

Joined: Thu Sep 25, 2008 10:33 am
Posts: 744
Location: Mars PA
I just got finished reading a post on the inter net that is disgusted with people trying to sell purplish red tourmaline as cuprian. The author shows a picture of what looks like a decent rich purplish pink and says that he has seen hundreds of tourmalines with the same color without copper. Therefor copper is not a chromophore in the pictured tourmaline and it should not be called cuprian.

I am sure his observations on purplish pink tourmaline are valid, but is the eye a valid way of differentiating regular tourmaline from cuprian tourmaline when the difference is based on color, NO! (I could have used paraiba type and paraiba like for my comparison, but I kept with the color in the post) With a spectrometer I can distinguish a Rubellite from a cuprian purplish red tourmaline. If the tourmaline shows the copper absorption peaks, then it effects the color of the stone. Copper is therefor a chromophore in that tourmaline, despite having thousands of other tourmaline that are only colored by manganese and iron and have the same color.

I think it is fair to call a tourmaline that shows the copper absorption curves, despite its color, to be called cuprian. This is certainly not universal. I have heard that some labs want a certain amount of copper in the tourmaline to be cuprian, while other sources use cuprian to designate any tourmaline colored by copper that did not ;come from Brazil. I know the GIA uses a spectrometer to test all of the submitted tourmalines if copper is suspected to be present.

So what do you think? I find it unfortunate that some tourmaline meets the letter of the definition of cuprian tourmaline, without having any exceptional qualities. And I certainly wouldn't spent a premium on them, but it is being done.

Bruce


Top
 Profile  
Reply with quote  
 Post subject: Re: Calling a purplish red tourmalinle, cuprian
PostPosted: Tue Mar 14, 2017 12:28 am 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 2603
Location: North Carolina
Personally, I find copper-bearing tourmaline just a bit more interesting even if the appearance is essentially the same. I wouldn't pay a big premium for it, but that's more because I'm a huge chintz on some things. 'Cuprian' isn't a nomenclature hill that I would fight for, much less die on. That said I'm also not particularly invested in the fight over 'paraiba/paraiba-type' so that would track.


Top
 Profile  
Reply with quote  
 Post subject: Re: Calling a purplish red tourmalinle, cuprian
PostPosted: Tue Mar 14, 2017 3:10 am 
Offline
Established Member

Joined: Wed Jan 18, 2017 1:08 pm
Posts: 27
Location: Bergisches Land
Hello,
for my part i can say that i am kind of amused seeing what a tiny amount of Copper can do to some traders phantasies.In my eyes a beautiful Tourmaline is ---a beautiful Tourmaline,whatever its chemistry is.Reminds me a bit on the long lasting debate over Emeralds which have to be Chromium-coloured,or Vanadium as well,or both or...
never mind, just my 2cents :D
best wishes
Gemse


Top
 Profile  
Reply with quote  
 Post subject: Re: Calling a purplish red tourmalinle, cuprian
PostPosted: Sat Mar 18, 2017 11:34 am 
Offline
Gemology Online Veteran

Joined: Thu Sep 25, 2008 10:33 am
Posts: 744
Location: Mars PA
I am still working to get my upgraded spectrometer back on line. What I hope to show with it, is that two tourmalines that have the same color from different chromaphores do not have the visual impact. I will be taking tone values into consideration. In other words even if a different set of chromophores can produce the same color as a copper based tourmaline, the copper based gemstone will have a brighter more vivid glow like quality. I fully appreciate that these improved qualities of copper based tourmaline maybe limited to highter quality gemstones.

Bruce


Top
 Profile  
Reply with quote  
 Post subject: Re: Calling a purplish red tourmalinle, cuprian
PostPosted: Sun Mar 19, 2017 10:29 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 18199
Location: San Francisco
Make sure that your observations are not anecdotal, Bruce.
Unbiased empirical evidence would be difficult to substantiate.


Top
 Profile  
Reply with quote  
 Post subject: Re: Calling a purplish red tourmalinle, cuprian
PostPosted: Sat Sep 02, 2017 11:26 am 
Offline
Active Member

Joined: Thu Aug 20, 2009 10:36 am
Posts: 95
Location: New York
Hello all,

I am a bit late to this discussion, but I will take a moment to comment from the position of AGL. There are many such purplish pink tourmalines that get submitted to our lab in hopes of getting a Paraiba or Paraiba-type designation. For us, since this is a color that is commonly found without the presence of Cu, we just call such stones: Natural Tourmaline, with the appropriate color description and we make the following statement in the comments section of our report:

This tourmaline possesses traces of the element copper however its color falls outside of the range that AGL describes as Paraiba-type tourmaline.

For us, the range of color in Paraiba or Paraiba-type tourmalines can be quite broad however Cu has to be influencing the observed color. Meaning the color of the gem has to be outside of the range one normally finds when just colored by Fe and/or Mn. And of course it has to possess Cu...

Also just to clarify here, while we are on this topic, at AGL we only use the term 'Paraiba' when the origin has been determined to be Brazil. If an origin is not requested or Mozambique, Nigeria is determined as the origin, we utilize the term 'Paraiba-type', with an accompanying comment that explains what we mean by this term.

Best regards,
Christopher P. Smith


Top
 Profile  
Reply with quote  
 Post subject: Re: Calling a purplish red tourmalinle, cuprian
PostPosted: Thu Sep 14, 2017 5:16 pm 
Offline
Valued Contributor

Joined: Sun Mar 08, 2009 2:16 pm
Posts: 327
Am I understanding that the Cu bearing purplish tourmaline's color is not affected by the Cu? In order for the stone to change to the blue/green types, the Cu has to be thermally activated to exchange with the Mn, correct?

It would be an interesting study and I would like to see the visuals as well as spectra from Bruce.


Top
 Profile  
Reply with quote  
 Post subject: Re: Calling a purplish red tourmalinle, cuprian
PostPosted: Thu Sep 14, 2017 7:41 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 2603
Location: North Carolina
Do the purplish-pink (ie, typical manganese colors) stones actually tend to go blue when heated? Obviously the rich violet-purple ones do, but they seem to mostly be showing a combination of the copper cyan blue with manganese pink, with heat at least acting to knock down the pink component (and no doubt having some effect on the blue though exactly what is probably uncertain).


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 8 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