Calling all spinel (and chemistry) experts!

[Autumn in New England]

Hello all,

I'm really wishing I had paid closer attention to Br. Lou in chemistry class now. I purchased 1.5mm, eye clean, vivid blue cobalt spinels from Vietnam to halo another spinel. I had been looking for 2mm, but these were the largest (only!) ones I could find, and cost $8k/ct. Anyway, I happened to be speaking to another vendor friend of mine who says he has gahnite (a member of the spinel group) from Nigeria for only $50/2.2mm, eye clean. Obviously that's a huge price difference (and I like the larger size). He says they're a deeper royal blue, no gray or green. My question is whether one variety is superior to another or rarer/more valuable? Would it account for the huge disparity in price points? He swears the gahnite contains cobalt... the formula I found is ZnAl2O4. The formula for true spinel is MgAl2O4. Neither mentions cobalt, so I assume that comes into play via mineral traces in the crystal structure of different colors/varieties? I'm lost. And I don't want to seriously over-pay for the same thing.

Thank you!
Autumn

P.S. Here's an article I found from the GIA. It doesn't help much... it refers to gahnite as a zinc spinel. But then it also mentions cobalt absorption spectra.

Blue Gahnite from Nigeria | Gems & Gemology

LA-ICP-MS analysis helps researchers better understand the composition of this type of spinel from Nigeria.

www.gia.edu

 

[voce]

I will try to answer as clearly and simply as possible. Yes, the gahnite contains cobalt--in trace amounts, just as the Vietnamese cobalt spinel contains cobalt in trace amounts. The chemical difference between the two varieties is in the crystal structure, in which gahnite is ZnAl2O4, and Vietnamese cobalt spinel is MgAl2O4. They are not chemically identical, but are chemically similar. Their chemical similarity makes for a similar color if the specimen has the same concentrations of cobalt and iron.

Yes, the Vietnamese cobalt spinel will be much, much more expensive. I believe this is because the source of the material has been mined out, for the most part. Gahnite in Nigeria is a newer find, and there is more material available.

 

[fredflintstone]

Hello all,

I'm really wishing I had paid closer attention to Br. Lou in chemistry class now. I purchased 1.5mm, eye clean, vivid blue cobalt spinels from Vietnam to halo another spinel. I had been looking for 2mm, but these were the largest (only!) ones I could find, and cost $8k/ct. Anyway, I happened to be speaking to another vendor friend of mine who says he has gahnite (a member of the spinel group) from Nigeria for only $50/2.2mm, eye clean. Obviously that's a huge price difference (and I like the larger size). He says they're a deeper royal blue, no gray or green. My question is whether one variety is superior to another or rarer/more valuable? Would it account for the huge disparity in price points? He swears the gahnite contains cobalt... the formula I found is ZnAl2O4. The formula for true spinel is MgAl2O4. Neither mentions cobalt, so I assume that comes into play via mineral traces in the crystal structure of different colors/varieties? I'm lost. And I don't want to seriously over-pay for the same thing.

Thank you!
Autumn

P.S. Here's an article I found from the GIA. It doesn't help much... it refers to gahnite as a zinc spinel. But then it also mentions cobalt absorption spectra.

Blue Gahnite from Nigeria | Gems & Gemology

LA-ICP-MS analysis helps researchers better understand the composition of this type of spinel from Nigeria.

www.gia.edu

Did I understand you right, 8K a carat as in $8000.00 dollars? If so, hold on! Don't do it! They are expensive but that is ridiculous. RUN!!!

Yes, the top colored Jedi blue cobalt Spinels are the best, better than any other blue Spinel in the world unless a new find has occurred I don't know about.

I could see $1000K to 2000k, but there are so few on the market it is hard to compare, but not $8000 for 2 mm melee...

PASS! PLEASE!

 

[fredflintstone]

Oh, I see you already bought them and are 1.5 mm. Send them back if you can.

 

[cloud_less]

I was looking at cobalt spinel as well! Here's what I gathered from sources like GIA research report (and some distant chem classes..)

MgAl2O4 and ZnAl2O4 (gahnite, aka zinc spinel) are the basic 'building blocks' of spinel crystal lattice.
Presence of elements such as iron, cobalt and chromium in trace amount is what gives spinel their color as they occationally replace Mg/Zn/Al's place in the crystal. However the question is How Much?

Cobalt gives a neon blue color whereas iron can make the crystal gray-blackish blue. Usually both are present but the amount and ratio vary. Vietnamese cobalt spinels contain cobalt in much higher amount compared to spinels elsewhere, making it the main chromophore element. And thus their prized vivid blue color.

The vendor is right to say that gahnite contains cobalt, but since it is overpowered by iron it tends not to have the neon color but a deeper blue.
(" The visible spectrum showed significant cobalt absorption bands (figure 3) between 500 and 620 nm, with additional contribution from iron absorption bands modifying the cobalt absorption spectrum", source
"The gahnite from Nigeria is mainly colored by cobalt but because of iron, its color does not qualify for cobalt-spinel color even if attractive.", source)

 

[cloud_less]

Yes, the top colored Jedi blue cobalt Spinels are the best, better than any other blue Spinel in the world unless a new find has occurred I don't know about.

Sorry for threadjacking!
Fred, I read an article a while ago that 'cobalt-blue' spinel has been found in Tanzania's Mahenge region just this May (source, source). They claim some of them have that bright blue color like the ones found in Luc Yen, but of larger size and better clarity. From pictures I saw I thought the color was a bit more inky than neon, but I'm not sure as I didn't have the chance to see a lot of them. I was talking to a vendor and he said he saw some at JCK and the price was crazy high wondering how that might change the market

 

[fredflintstone]

Sorry for threadjacking!
Fred, I read an article a while ago that 'cobalt-blue' spinel has been found in Tanzania's Mahenge region just this May (source, source). They claim some of them have that bright blue color like the ones found in Luc Yen, but of larger size and better clarity. From pictures I saw I thought the color was a bit more inky than neon, but I'm not sure as I didn't have the chance to see a lot of them. I was talking to a vendor and he said he saw some at JCK and the price was crazy high wondering how that might change the market

Just looked up the Mahange cobalt blue Spinels.

Here is an article on the find from National Jeweler (a trade publication) with several stones pictured. From what I see of these Spinel's, they are not as vivid as the Luc Yen, Vietnam stones. But they are nice.

Beware though, a few years back they discovered cobalt diffused Spinels in Sri Lanka. These stones cost way to much to be bought without a legitimate re[port.

A New Source in Tanzania Is Producing Cobalt-Blue Spinel

The stones come from a deposit close to Mahenge and have been on the market for several months.

www.nationaljeweler.com

 

[Autumn in New England]

I will try to answer as clearly and simply as possible. Yes, the gahnite contains cobalt--in trace amounts, just as the Vietnamese cobalt spinel contains cobalt in trace amounts. The chemical difference between the two varieties is in the crystal structure, in which gahnite is ZnAl2O4, and Vietnamese cobalt spinel is MgAl2O4. They are not chemically identical, but are chemically similar. Their chemical similarity makes for a similar color if the specimen has the same concentrations of cobalt and iron.

Yes, the Vietnamese cobalt spinel will be much, much more expensive. I believe this is because the source of the material has been mined out, for the most part. Gahnite in Nigeria is a newer find, and there is more material available.

This is very helpful, thank you!

 

[Autumn in New England]

I was looking at cobalt spinel as well! Here's what I gathered from sources like GIA research report (and some distant chem classes..)

MgAl2O4 and ZnAl2O4 (gahnite, aka zinc spinel) are the basic 'building blocks' of spinel crystal lattice.
Presence of elements such as iron, cobalt and chromium in trace amount is what gives spinel their color as they occationally replace Mg/Zn/Al's place in the crystal. However the question is How Much?

Cobalt gives a neon blue color whereas iron can make the crystal gray-blackish blue. Usually both are present but the amount and ratio vary. Vietnamese cobalt spinels contain cobalt in much higher amount compared to spinels elsewhere, making it the main chromophore element. And thus their prized vivid blue color.

The vendor is right to say that gahnite contains cobalt, but since it is overpowered by iron it tends not to have the neon color but a deeper blue.
(" The visible spectrum showed significant cobalt absorption bands (figure 3) between 500 and 620 nm, with additional contribution from iron absorption bands modifying the cobalt absorption spectrum", source
"The gahnite from Nigeria is mainly colored by cobalt but because of iron, its color does not qualify for cobalt-spinel color even if attractive.", source)

Thank you for this!! That was my understanding, too, that the iron content is the difference. I suppose it's much like ruby... a higher iron content negatively impacts the effect of the chromium, darkens the stone, and quenches fluorescence.

 

[Autumn in New England]

Did I understand you right, 8K a carat as in $8000.00 dollars? If so, hold on! Don't do it! They are expensive but that is ridiculous. RUN!!!

Yes, the top colored Jedi blue cobalt Spinels are the best, better than any other blue Spinel in the world unless a new find has occurred I don't know about.

I could see $1000K to 2000k, but there are so few on the market it is hard to compare, but not $8000 for 2 mm melee...

PASS! PLEASE!

Yep, $8k/ct. I needed 20 (1.5mm) stones, which was $2,400. Do you know of anyone who carries these guys in matched melee sizes though? Because, other than the gahnite, which I'm now convinced is not what I'm looking for, I could not find any other vendors who had top color/eye clean Vietnamese cobalt spinel melee. And I think that's why this particular vendor priced them so high. She believes they are irreplaceable... and I pretty much bought the last of them.

 

[fredflintstone]

I can check with some of my old Vietnam sources. Cannot promise anything.

I suppose if the were cut very good & eye clean with top color like you wrote, they would not be cheap, as these stones are famous for wonky cutting, as bad as Kyanite, LOL! And I suppose that if all the above is true and they are very hard to find like that, yes the price would be high. Not really sure if it should be that high though but I have been wrong before.

Though in all sincerity if that is what you must have, well, that is what you must have. There is Sapphire that color and much cheaper. I would send them to a lab. for that amount of money and small size. At least one, because to send them all would cost a fortune.

I'm sorry, but I'm just very suspicious of cobalt blue Spinel's, maybe more so than I need. But the rarity, the price, the color, makes them very susceptible to synthetic or diffusion.

I'll let you know if I find anything.

 

[Rfisher]

If they truly are irreplaceable….

Did you buy extras to stash away in case of loss or damage?

 

[Autumn in New England]

I can check with some of my old Vietnam sources. Cannot promise anything.

I suppose if the were cut very good & eye clean with top color like you wrote, they would not be cheap, as these stones are famous for wonky cutting, as bad as Kyanite, LOL! And I suppose that if all the above is true and they are very hard to find like that, yes the price would be high. Not really sure if it should be that high though but I have been wrong before.

Though in all sincerity if that is what you must have, well, that is what you must have. There is Sapphire that color and much cheaper. I would send them to a lab. for that amount of money and small size. At least one, because to send them all would cost a fortune.

I'm sorry, but I'm just very suspicious of cobalt blue Spinel's, maybe more so than I need. But the rarity, the price, the color, makes them very susceptible to synthetic or diffusion.

I'll let you know if I find anything.

Thank you! Yeah, they do need to be spinel (though I agree about the sapphire), as the center stone is a jedi red, and I just think the pairing would be super cool. I purchased them from a trusted PS vendor who has them batch tested.

 

[Autumn in New England]

If they truly are irreplaceable….

Did you buy extras to stash away in case of loss or damage?

No, but I should!!

 

[Rfisher]

I can’t wait to see them and the spinel they are to surround.

Hope you show some of your - but even just vendor shots are lovely

 

[cloud_less]

Thank you! Yeah, they do need to be spinel (though I agree about the sapphire), as the center stone is a jedi red, and I just think the pairing would be super cool. I purchased them from a trusted PS vendor who has them batch tested.

This sounds absolutely AMAZING!!! Can't wait to see pics
I was thinking about a two-stone project with a Jedi red and a cobalt spinel but found it so hard to get a reasonably priced true Jedi

 

[Autumn in New England]

I can’t wait to see them and the spinel they are to surround.

Hope you show some of your - but even just vendor shots are lovely

Thank you! Here's the vendor pic of the red spinel. I'm a terrible photographer, but I will try to take my own shot too.

And here's my (yep, perennially fuzzy) shot of the blue spinel. They're well-matched in person... the glare is sort of washing some out.



And here's what I have in mind for the design...

 

[Rfisher]

That will be a-ma-ZING!!!!

 

[cloud_less]

Can't imagine how insanely gorgeous your finished ring would be!!

 

[Autumn in New England]

This sounds absolutely AMAZING!!! Can't wait to see pics
I was thinking about a two-stone project with a Jedi red and a cobalt spinel but found it so hard to get a reasonably priced true Jedi

Thank you!! Welp, everyone has a different idea of what a true jedi entails. For me, it means the stone never goes dark, so a medium tone, and has vivid saturation. IMO, it should also fluoresce strongly. Some prefer a more pink stone... I like the purer reds. I found the cobalt spinel to be the harder of the two to source by far! The jedis are out there if you want to pay. Good luck in your hunt!!

 

[Autumn in New England]

That will be a-ma-ZING!!!!

Can't imagine how insanely gorgeous your finished ring would be!!

Aww thanks, friends! Now you're getting me excited!! You see everyone's rare beauties here, and sometimes you start to think your stuff isn't so remarkable after all, you know? So I appreciate the encouragement!!

 

[Autumn in New England]

P.S. I also think it would be a better contrast if the inner halo were diamond and the outer halo were the cobalt spinels. But that was impossible to find, even if I wanted to spend a fortune (I don't)!!

 

[qubitasaurus]

I dont think Im an exoert at either but I'm pretty sure that we label gemstone varieties like tourmaline or spinel by their chemical composition (like one chemical formula and lattice per variety). Whenever you've got something that is flourescent you're dealing with a dopant in the material which has replaced certain (usually a minite number of) positions in the lattice, but typically this alters the bond structure arround these lattice locations, leading to an electron in some orbital of the cobalt that typically can be excited, this produces an abrorbtion spectrum, but you can also get fluorescence from decay of this electron. Which is why you can have such different properties for copper doped and cobalt doped or vanadium doped material. I could swear this has come up before and maybe I even took some photos at the Oxford museum of it (but actually if these photos are unrelated haha then I apologise as I can't read them before posting).

 

[Autumn in New England]

I dont think Im an exoert at either but I'm pretty sure that we label gemstone varieties like tourmaline or spinel by their chemical composition (like one chemical formula and lattice per variety). Whenever you've got something that is flourescent you're dealing with a dopant in the material which has replaced certain (usually a minite number of) positions in the lattice, but typically this alters the bond structure arround these lattice locations, leading to an electron in some orbital of the cobalt that typically can be excited, this produces an abrorbtion spectrum, but you can also get fluorescence from decay of this electron. Which is why you can have such different properties for copper doped and cobalt doped or vanadium doped material. I could swear this has come up before and maybe I even took some photos at the Oxford museum of it (but actually if these photos are unrelated haha then I apologise as I can't read them before posting).

My chemistry teacher would be very proud of you! Thank you for the insight!!

 

[Double E]

It’s a very luxurious idea of such ring! I mean, you know, Jedi + Cobalt~

Is the Jedi from Antony btw?

 

[Daisys and Diamonds]

Thank you! Here's the vendor pic of the red spinel. I'm a terrible photographer, but I will try to take my own shot too.

And here's my (yep, perennially fuzzy) shot of the blue spinel. They're well-matched in person... the glare is sort of washing some out.



And here's what I have in mind for the design...

oh wow
that's going to be amazing

i am watching closely as a learning experience

 

[qubitasaurus]

My chemistry teacher would be very proud of you! Thank you for the insight!!

Lol thanks, I think mine might shudder as I slept my way through chemistry, and broke most of the glass ware in the labs. I proceeded to sleep (in the second row) of solid state physics for a semester which was god awfully boring (sensing a pattern), so I think maybe I'm not the most informed about this topic and anything I say should be taken with a grain (probably a packet) of salt. But it made me smile to think at least one of the lectures somewhere there may not roll their eyes at me.

 

[Autumn in New England]

Lol thanks, I think mine might shudder as I slept my way through chemistry, and broke most of the glass ware in the labs. I proceeded to sleep (in the second row) of solid state physics for a semester which was god awfully boring (sensing a pattern), so I think maybe I'm not the most informed about this topic and anything I say should be taken with a grain (probably a packet) of salt. But it made me smile to think at least one of the lectures somewhere there may not roll their eyes at me.

I remember Br. Lou (HS chemistry) gave us an entire lecture one day, and I, confused, asked a question. After a long pause, his response was, "wait, this is all wrong," and he proceeded to erase the board. lol Everyone collectively eye rolled and flung their papers in the air.

 

[Autumn in New England]

It’s a very luxurious idea of such ring! I mean, you know, Jedi + Cobalt~

Is the Jedi from Antony btw?

Thank you! Actually, I purchased that guy from Instagram. The shop name escapes me at the moment. I had it certified by Lotus.

I do feel I should mention though that I did return a red spinel to Antony. I always sing RGC's praises, so it seems only fair I should also detail a disappointment. This was a couple of years back. It was a red spinel heart, which really excited me, because how often do you see that shape in fine material?! I fully expected to love it, since everything else had exceeded my expectations. It was listed as top color, and indeed it was a bright red with a perfect medium tone. However, the saturation fell short of ideal by just a hair, IMO. That was my first and only failed purchase with RGC. I am uber fussy with spinel though, so do consider that! The return process was very smooth.

 

[LilAlex]

My question is whether one variety is superior to another or rarer/more valuable?

Reading all this with interest. It looks like they are at least the same hardness which is a big win for the cheaper material. I had not heard of gahnite/zinc spinel.