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 Post subject: Re: Spodumene Investigation
PostPosted: Fri Oct 10, 2014 3:22 pm 
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For the record, I have yet to see any Cr-spodumene from Brazil which I would call hiddenite. It always seems to be a relatively faint or moderate minty green rather than an emerald green (ie, if they were beryl they wouldn't qualify as emerald). Does properly green material exist out of there, or is it all that way? My NC hiddenites and Afghan hiddenites don't seem to fluoresce at all. So maybe there's just not enough in the Brazilian stuff to kill fluorescence entirely. Vanadium also may play a role in the color as seen in the GIA investigation of Afghan hiddenite so maybe there's some of that to it.
Side note: Cr also seems to kill spodumene's response to irradiation (though I've been having trouble finding the paper that said that again). So that's interesting.

Second side note: while I do have a few very intensely saturated Afghan hiddenites they don't have the same pure awesome green of the NC ones I have. It seems to have more yellow and overall doesn't quite match the saturation. I don't know why that would be but there you have it. Still a very beautiful gem.

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 Post subject: Re: Spodumene Investigation
PostPosted: Fri Oct 10, 2014 5:04 pm 
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I agree that the best of the NC hiddenite is superior to the Afghani material but I think part of the problem is that none of the Afghani rough I have seen could be cut on the c axis which is the direction of most intense green. I have also seen a fair amount of NC material that was only so-so in color.


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 Post subject: Re: Spodumene Investigation
PostPosted: Sun Oct 12, 2014 5:14 am 
Attachment:
kunzite UV 01.JPG
kunzite UV 01.JPG [ 48.37 KiB | Viewed 2067 times ]
Attachment:
kunzite UV.JPG
kunzite UV.JPG [ 55.27 KiB | Viewed 2075 times ]
Was working with the kunzite & the UVLW light & this is what I came up with, good responce with this stone-steve... =D> 8)


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 Post subject: Re: Spodumene Investigation
PostPosted: Sun Oct 12, 2014 11:24 am 
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The color of the fluorescence I have been seeing with unstable color is orange.

Anyone else with UV results?


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 Post subject: Re: Spodumene Investigation
PostPosted: Sun Oct 12, 2014 1:31 pm 
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Tried to take a couple quick pics with my ipad....first is my pale spodumene in daylight. Next is with a LWUV laser penlight in the dark, and finally with both UV and daylight.

I cut it thinking it was a tourmaline (ha!)

My husband has an Afghani pale green crystal...it also fluoresces orange.


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 Post subject: Re: Spodumene Investigation
PostPosted: Sun Oct 12, 2014 3:15 pm 
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I'm interested simply in the relationship of fluorescence and color stability.


I'm afraid such correlation does not exist. The fluorescence (essentially a strong broad luminescence band having maxima between 590 and 610 nm) is assigned to hole center captured by Al3+ atoms. Mn intensifies this luminescence band, while Fe quenches it.

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 Post subject: Re: Spodumene Investigation
PostPosted: Sun Oct 12, 2014 4:07 pm 
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Oh, hell.

Then, it is simply coincidence that every fluorescent spodumene I have has faded and every non-fluorescent sample has not?

Nevermind.


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 Post subject: Re: Spodumene Investigation
PostPosted: Sun Oct 12, 2014 10:28 pm 
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Barbra Voltaire wrote:
The color of the fluorescence I have been seeing with unstable color is orange.

Anyone else with UV results?


The kunzite from the Oceanview Mine in California fluoresces pink to pinkish-orange in SW UV and pinkish-orange to orange in LW UV. It is very fade-resistant. The yellow spodumene from the Pala Chief Mine, which is about 500 yards away in a pegmatite that's one layer higher fluoresces orange in LW UV and has no response to SW UV. It's completely stable. The kunzite from Pala Chief shows the same pattern of fluorescence as the Oceanview. However, in general it is a paler pink color. It does not seem to fade very much over time. I've found pieces lying in the sun for potentially ages that are still a pale pink. I suspect that if treated they would turn much darker and likely fade very slowly. I have colorless pieces from the Oceanview and some fluoresce exactly like the kunzite and some are barely fluorescent at all.

I have some purple Afghan kunzite that is relatively stable and it shows the same pattern as the Oceanview material.

I bought a parcel of Afghan kunzite in 2012 and sent it off to Brazil to get faceted and treated. I wish I had saved one photo they sent me after the Cobalt-60 treatment but before the heat annealing process. It was all varying shade of deep green. Quite beautiful in fact. Once it was heated to anneal the color a lot of it became a much paler pink-purple. Some stayed darker purple and very similar to the California untreated material I had faceted at the same time. Within less than a year, a large proportion of the Afghan material completely faded to very pale pink/purple or colorless. A small percentage still has good color 20 months later. I had checked fluorescence before I sent it off, and the most intensely fluorescent pieces were also already a light kunzite color, and they are the ones that have remained a good color.

This is my theory on the fluorescence of kunzite specifically: Spodumene containing manganese (Mn) will fluoresce an orange color. The greater the total concentration of Mn, the more intense the fluorescence. From what I can find in the literature online, Mn(II) (Manganese in the +2 oxidation state) fluoresces orange. Given that I've only seen the more pink tones in the purple kunzites, I suspect that Mn(III) is what's responsible for that color of fluorescence.

The reality is that ALL spodumene colored by Mn will fluoresce and ALL will eventually fade. It's just the time frame for that fading to occur that varies. As studies have shown, the relative concentration of Mn and most importantly the Mn/Fe ratios are key to both the depth of color and the the speed at which material fades. Because Mn(III) and Mn(II) are strong oxidizing agents, they scavenge electrons away from anything else that is available to give them up. Most often, this is Iron, but it can be other trace elements.

Jeff

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 Post subject: Re: Spodumene Investigation
PostPosted: Sun Oct 12, 2014 11:30 pm 
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Jeff: thank you by the way for your fantastic and information-rich posts here. It's awesome to be able to tap in to your depth of experience with this gem.
A while back I made a thread asking about the stability of yellow spodumene. This was one of the responses I got:
stairman wrote:
I have some that was dug personally out of the oceanview mine in pala ,ca (i know the blasting crew) and in a year it went from a pale lemony yellow to almost clear while sitting in a draw of my facetting station.But that's anecdotal...my only experience with the stuff

Maybe he was simply looking at it under incandescent light which killed the color? I've certainly had that feeling between looking at yellow spodumene under fluorescent and incandescent light.


It's also interesting to note that pink/purple jadeite is colored by exactly the same manganese substitution (and the same chromium substitution for emerald green material), in exactly the same crystal structure, with the only difference being Na substituted for Li, and yet! it is not known to fade. What the heck.

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 Post subject: Re: Spodumene Investigation
PostPosted: Mon Oct 13, 2014 11:17 am 
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Scarodactyl wrote:
Jeff: thank you by the way for your fantastic and information-rich posts here. It's awesome to be able to tap in to your depth of experience with this gem.
A while back I made a thread asking about the stability of yellow spodumene. This was one of the responses I got:
stairman wrote:
I have some that was dug personally out of the oceanview mine in pala ,ca (i know the blasting crew) and in a year it went from a pale lemony yellow to almost clear while sitting in a draw of my facetting station.But that's anecdotal...my only experience with the stuff

Maybe he was simply looking at it under incandescent light which killed the color? I've certainly had that feeling between looking at yellow spodumene under fluorescent and incandescent light.


It's also interesting to note that pink/purple jadeite is colored by exactly the same manganese substitution (and the same chromium substitution for emerald green material), in exactly the same crystal structure, with the only difference being Na substituted for Li, and yet! it is not known to fade. What the heck.


Thanks for your kind words. I'm a scientist by training and my tendency is to just dig in to any topic I'm interested in. When I was a boy I thought I would study to become a mineralogist. Alas, the seduction of the biological sciences led me astray!

I believe you are correct with the observation by stairman. I also suspect that what he has is a Pala Chief piece--the two mines are owned by the sam individual and crew works in both. Virtually no yellow spodumene has been found in the Oceanview, but a huge pocket of it was found in the Pala Chief in late 2011. I have some spectacular crystals from that pocket and hundreds of carats of faceted gems. If you'd like a smaller crystal I can send one, just PM me--I have a few kilos of small crystals and shards. It does look very pale straw yellow in daylight or incandescent light, but is a brilliant yellow in fluorescent light, and even looks greenish down the c-axis in fluorescent light. I actually had a friend and master gem cutter, Stephen Kotlowski, facet what is to the best of our knowledge the largest faceted US triphane (personally I like the short name to distinguish yellow gem spodumene from the pink/purple kunzite and green hiddenite). It came in at 150.35 carats and was remarkable; its now in a public teaching collection.

With regards to jadeite, it is in the same family of clinopyroxenes, but the crystal structure at the molecular level is different enough to matter. If you've read the 2012 article in Gems & Gemology, you'll recall that there is a small difference in the relative distance between the M1 octahedral sites in crystals of the two minerals. Given that this is the critical site for substitution in the crystal lattice by chromophores like Fe, Cr and Mn, that is important, as paired interactions between adjacent M1 sites can now come in to play. I would hypothesize that the structure of spodumene crystals is such that when the ratios of Mn and Fe are right, the pairing structure is such that you get a form of Mn+3(+4)/Fe+2 IVCT (intervalence charge transfer) which leads to the reduction of the Mn and therefore the loss of the pink/purple color. In jadeite my theory would be that the structure is such that this transfer is not easily facilitated. In addition, most jadeite is either cryptocrystalline or polycrystalline form, which would significantly alter the ability for charge transfer to be possible.

BTW, in relation to the topic in this thread, you'll note that the G&G article suggests the use of UV fluorescence as a method of ascertaining the presence of Mn in jadeite.

The sources of color in minerals is fascinating...I have toyed with the idea of going back to grad school to study the topic, but I'm bit too old for that I think. Well, not old, but life and family responsibilities make it less than feasible at this point.

Jeff

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 Post subject: Re: Spodumene Investigation
PostPosted: Mon Oct 13, 2014 12:27 pm 
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Your post is magnificent Jeff! It was really informative.

Quote:
The reality is that ALL spodumene colored by Mn will fluoresce and ALL will eventually fade.


It is theoretically possible that fluorescent spodumene colored with Mn, may appear to be color stable if it had already faded to a light tone before purchase, right?


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 Post subject: Re: Spodumene Investigation
PostPosted: Mon Oct 13, 2014 12:57 pm 
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Alnitak wrote:
Thanks for your kind words. I'm a scientist by training and my tendency is to just dig in to any topic I'm interested in. When I was a boy I thought I would study to become a mineralogist. Alas, the seduction of the biological sciences led me astray!

I followed the exact opposite path--biology to geology. On the plus side I got a chem minor along the way so it's all for the best!
Alnitak wrote:
If you'd like a smaller crystal I can send one, just PM me--I have a few kilos of small crystals and shards.

Wow, thanks! I have a fair number of Afghan specimens but none from California. I'll send a PM.
Alnitak wrote:
(personally I like the short name to distinguish yellow gem spodumene from the pink/purple kunzite and green hiddenite).

Absolutely. It's a good-sounding name too!
Alnitak wrote:
With regards to jadeite, it is in the same family of clinopyroxenes, but the crystal structure at the molecular level is different enough to matter. If you've read the 2012 article in Gems & Gemology, you'll recall that there is a small difference in the relative distance between the M1 octahedral sites in crystals of the two minerals.

Oh yes, absolutely. The fact we don't see a whole lot of solid solution in nature between the two shows that there are important differences--though apparently natural spodumenes can be up to 9% Na and synthetics can get up to 54% (at which point I guess you're really dealing with an Li-rich jadeite). I wonder if that or any other substitution could play some role in stability by shifting the structure around a bit.
Alnitak wrote:
The reality is that ALL spodumene colored by Mn will fluoresce and ALL will eventually fade.

I assume this means in the absence of sufficient iron (or whatever it is) to quench the fluorescence. I do have a few samples with nice pink color which neither fluoresce nor phosphoresce, even with the power of my UV laser.

Alnitak wrote:
The sources of color in minerals is fascinating...I have toyed with the idea of going back to grad school to study the topic, but I'm bit too old for that I think.

I'd love to work on that as well. Alas, you'd have to be really lucky to find a place and an advisor that would actually allow for studying it. Trace element analyses aren't free, after all. Probably the sort of pursuit what would be best accomplished by the independently wealthy.

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Last edited by Stephen Challener on Mon Oct 13, 2014 2:48 pm, edited 1 time in total.

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 Post subject: Re: Spodumene Investigation
PostPosted: Mon Oct 13, 2014 1:27 pm 
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Scarodactyl wrote:
Alnitak wrote:
The sources of color in minerals is fascinating...I have toyed with the idea of going back to grad school to study the topic, but I'm bit too old for that I think.

I'd love to work on that as well. Alas, you'd have to be really lucky to find a place and an advisor that would actually allow for studying it. Trace element analyses aren't free, after all. Probably the sort of pursuit what would be best accomplished by the independently wealthy.


I have to raise my hand here and say "yes, me too! I want to study the causes of color in gemstones."


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 Post subject: Re: Spodumene Investigation
PostPosted: Mon Oct 13, 2014 1:46 pm 
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Just a thought (cough cough).....Alberto, Mikko how does GemmoLIBS sound to you? I think it has a nice ring to it myself. 8)


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 Post subject: Re: Spodumene Investigation
PostPosted: Mon Oct 13, 2014 3:47 pm 
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Barbra Voltaire wrote:
Just a thought (cough cough).....Alberto, Mikko how does GemmoLIBS sound to you? I think it has a nice ring to it myself. 8)


are you able to read in our minds??? kidding aside, GemmoLIBS is already a project but it temporarily taken a back seat, we realized there's no such thing as a decent gemmological UV-Vis-NIR spectrometer on the market so, after the GemmoFTIR, the GemmoUV-Vis-NIR has already taken shape in our lab.......... GemmoLIBS must wait for a while.......... 8) 8) 8)

ciao
albé

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