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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Wed Apr 16, 2014 3:03 pm 
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@Barbra: thanks, and nice to meet you as well! Nice site you have here :D
@Bill: Thanks, that means a lot coming from you!

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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Sun Apr 05, 2015 2:07 pm 
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A couple of interesting things I came across in the GIA's gemology project:
Chrome diopside with Cr peak but no V peak in EDXRF (0.91 ct Pyroxene (Diopside) - Chrome Diopside from Kenya (PDF)
All four peridots examined showed significant nickel peaks as well, which isn't much help since one is a nice Burmese green, one is an Arizona yellow-green and two are Egyptian stones somewhere in between.

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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Sun Apr 05, 2015 5:08 pm 
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Scarodactyl wrote:
Chrome diopside with Cr peak but no V peak in EDXRF

What were the reported relative sensitivities of Cr and V in that analysis?


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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Mon Apr 06, 2015 6:44 pm 
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Hi Bill -
Reading in the paper I see this: https://s3.amazonaws.com/gubelin/pyroxe ... -35385.pdf says "Our EDXRT method can detect most elements with higher atomic numbers than sodium (Z=11) in the Periodic Table; depending on the element, the lower limit of detection is between 1 and 100 parts per million (0.0001 to 0.01%)."

I note that there were two peaks in the graph for Chromium and none for Vanadium. and I also note the atomic number of vanadium is 23. (Chromium is 24).

I am not sure if this is what you were asking for, but it seems like it might be?

another paper here:http://www.icdd.com/resources/axa/vol42/v42_17.pdf has information about EDXRF in general whit detection limits for both Chromium and Vanadium:
has this:
Table 1. EDXRF
Element EDXRF Detection Limit (ppm)

Antimony 3
Arsenic 4
Barium 10
Cadmium 2
Chromium 8
Lead 5
Mercury 9
Nickel 5
Selenium 2
Silver 2
Thallium 6
Vanadium 20
Zinc 2


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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Mon Apr 06, 2015 9:43 pm 
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I'm not an expert in edxrf, unfortunately. It's not really quantitative without further info, and the above post seems to indicate its a bit less sensitive to V for some reason. So clearly I can't guarantee from this that there's no V present, but that's not really the point. This stone is most likely Cr colored at least in part.

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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Tue Apr 14, 2015 6:59 pm 
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a quick search on google came up with this quote:
Chrome-diopside is one of the main minerals contributing to this anomaly, having an average Cr content of 1505 ppm.

from this paper:
http://www.researchgate.net/publication ... ate_Brazil

If that is typical, then a sensitive to vandaium of 20ppm would surely have showed up if it were a major contributor to color.


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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Thu Oct 29, 2015 3:46 pm 
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I realize I'm on the late side here. The issue is that of chrome titanite (sphene) specifically from Pino Solo in Baja, Mx. Many years ago I personally collected and cut a decent sized chrome sphene from this site. I was sure I had done an absorption spec on this stone in the past. Moments ago, I confirmed. My stone definitely shows broad band far UV and far IR extinctions common to chromium. Although some locales for sphene may not have chromium as the chromophore, I submit that the Pino Solo material definitely does.


Last edited by ClassyCarat on Thu Oct 29, 2015 10:46 pm, edited 1 time in total.

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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Thu Oct 29, 2015 6:30 pm 
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I suspect that it is almost or entirely always true that any mineral that accepts vanadium as a chromophore will also accept chromium, though the color produced obviously isn't always the same. The two elements so similar in size and charge it's hard to imagine a crystal lattice being willing to accept one but not the other. The only example I can think of off the top of my head where there isn't much acknowledgement of V as a chromophore where Cr is implicated is topaz, though there are mentions of it here and there.

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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Fri Oct 30, 2015 5:27 pm 
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Is there vanadium in rubies ?


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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Fri Oct 30, 2015 6:35 pm 
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Vanadium does act as a chromophore in sapphire, as seen in the ever-popular purple-pink color change synthetics. Not identical but broadly similar in color.

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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Fri Oct 30, 2015 8:40 pm 
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Isi wrote:
Is there vanadium in rubies ?


Sometimes

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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Fri Jan 08, 2016 7:53 pm 
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There is a little bit of everything in everything. One must consider the limit of the detection of the method being used.


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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Sat Jan 09, 2016 12:38 am 
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Sidebar: I have been told there is a trace amount of gallium in every natural ruby*.

*University of Heidelberg


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 Post subject: Re: Confusing Chromophores Can Confuse Gemmos
PostPosted: Mon Jan 18, 2016 1:02 am 
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AWSOME timing! Just read this chapter in the colored stones curriculum. We have to do something about this language barrier though. Does Rosetta Stone teach chemistry as a second language?

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