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 Post subject: Green Zircon
PostPosted: Tue Jul 14, 2009 10:39 am 
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Can someone explain green zircon to me-are these stones radioactive? I have a rather large, somewhat hazy with small bubble inclusions. From a reputable dealer-multicolour.com.

I have heard the phrase metamict thrown around with green zircon. Are all green zircon in the metamict state?

thanks

I like to collect the rarer/odd ones so I was intrigued by the green zircon (which one doesn't often find).


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PostPosted: Tue Jul 14, 2009 11:12 am 
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The mineral zircon contains trace amounts of radioactive elements.
Over time, these elements (specifically hafnium and thorium) break down the crystal lattice of the zircon:

http://www.gemologyproject.com/wiki/ind ... tle=Zircon

I doubt the inclusions within your green zircon are bubbles. Use the term cautiously. :D


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PostPosted: Tue Jul 14, 2009 12:03 pm 
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Quote:
I have heard the phrase metamict thrown around with green zircon. Are all green zircon in the metamict state?


Frank and I discussed this recently in one of the chats.
this was the outcome:
All green zircons are metamict
not all metamict zircons are green.


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PostPosted: Tue Jul 14, 2009 8:12 pm 
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Not exactly on topic, but, I have found that zircon coming from Nigeria seems to be much more of the higher type and carries far better dispersion then zircon coming from other localities. Some of the African material, specifically around the Umba and Songea regions, can also be amazingly full of dispersion! I find a lot of zircon, regardless of cut, from other locals tends to be hit or miss for it.

Anyways, back on topic, thanks for the info on the green Tim, this was always an area that stumped me as well.


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PostPosted: Wed Jul 15, 2009 3:15 am 
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Quote:
Anyways, back on topic, thanks for the info on the green Tim, this was always an area that stumped me as well


I might have to add that this wasn't the outcome of a few years research on our behalf. Frank was taught by a very knowledgable Australian gemologist that all greens are metamict. I've encountered many colourless zircs in Australia that show no uranium line any more but I can't state with certainty that they are as far gone as the greens...

Jason laid hands on two greens the other week that were so metamict that their double refraction had diminished to non-existent. I'm pretty sure those Aussie clear ones still show some doubling.

Does somebody know a way to speed up the radioactive decay in zircs? It would be interesting to see if they all end up green after all.


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PostPosted: Wed Jul 15, 2009 4:46 am 
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I would like to know too... Because then the storing of radioactive waste from nuclear plants will be handled through my new company :D

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PostPosted: Wed Jul 15, 2009 4:51 am 
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geek ;)

radioactivity in zircs is much less than the levels in the stuff nuclear plants are putting out. Making it possible for zircs doesn't neccesarily mean we have solved the worlds radioactive waste problem. 8)

but you do have a point there :oops:


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PostPosted: Wed Jul 15, 2009 5:15 am 
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8)
I know about the low levels of radioactivity in Zirkons..
Actually I'm pretty happy they are, as cutting the stuff would otherwise be very unhealthy and I have cut a few during the years. The Zirkons I have tested with geiger counter have not stressed up the levels enough to differentiate from the background radiation.

A bit OT but speaking of hazards when cutting, Beryl dust is not to be inhaled. Be sure to wash off equipment before drying as the dust is slightly poisonous. At least this is what I have been thought and I act accordingly when cutting Beryl.

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PostPosted: Wed Jul 15, 2009 11:14 am 
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Keep in mind that a percentage of potassium is radioactive, enabling potassium/argon dating....but we still eat bananas.


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PostPosted: Wed Jul 15, 2009 12:36 pm 
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i understand what tim mentions--
"All green zircons are metamict
not all metamict zircons are green."

*probably a stupid question*
but what does it mean if the green zircon is termed as being "low metamict" or "high metamict??"
:oops:


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PostPosted: Wed Jul 15, 2009 3:40 pm 
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Hi Gingerkid,

I think Low metamict would be zircon which has shot it's radioactive bolt and has more or less lost it's crystalline nature. I'm not sure if the phrases low and high metamict are used often. Mostly I hear low zircons and high zircons...even medium. The low zircons are metamict. As the crystalline structure is broken down by the radioactive assault the RI of the stone is reduced as well as it's SG. The interesting thing about the change of SG is that this means the stone actually grows in size.

Low (metamict) zircon can be returned to a higher state by heating. This allows the amorphous atoms to realign into a crystalline lattice and raises the RI and SG. The stone will still weigh the same but it will shrink to a certain extent

another sign of low zircon as compared to high zircon can be seen with the spectroscope. with high zircon the lines seen tend to be sharp and narrow. As the zircon becomes metamict the lines get a little broader and fuzzier.

Be well

Frank


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PostPosted: Wed Jul 15, 2009 3:54 pm 
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Quote:
but what does it mean if the green zircon is termed as being "low metamict" or "high metamict??"


It means that the person who wrote it down is confusing the two terms. It's either low zircons (metamict) or high (unaffected by radioactive decay of their crystallinity)

(what Frank said)


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PostPosted: Wed Jul 15, 2009 5:56 pm 
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:) thanks for your explanations, frank and tim!

i found the gemology online chat on zircon. :wink:

green zircons are considered metamict and most are called "low" (lower refractive index) zircons. they are usually found in rivers as pebbles in sri lanka.

"low" and "intermediate/middle" zircon have undergone more extensive damage to the crystal lattice.

"high" (normal/high ri) zircons have their crystal lattice intact and is usually found in crystal form.


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 Post subject: Re: Green Zircon
PostPosted: Wed Sep 26, 2012 7:08 pm 
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Hi,

Quick question, the low metamict green zircons, is it usually singly refractive?? I got an OTL stone with SG 4 and I dont see any doubling at all... Specs shows moderately broad band around the 650-670 covering region. Polariscope ADR and looks SR

inclusions are spiral twinning like inclusions and whitish cloud

I have to eleminate Demontoid garnet due to lack of dispersion... so I am left with low metamict Zircon !

any views?

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 Post subject: Re: Green Zircon
PostPosted: Thu Sep 27, 2012 3:11 am 
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Hi
I would like to clear up a missconception about green Zircon-

Green zicons are all low Zircons- NO!
there are green Zircons with a high content of radioactive elements that are just not old enough, so the radioactive decay has just not begun to affect the stone-not enough time!
These stones are high Zircons but are already in an metamic state and show no (gemological) signs for the classifcation for the low Zircons. These green Zircons normaly have a higher radioactive content than low type green Zircon.
So there are high and low green Zircons
hope that helps

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