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).
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21602 Location: San Francisco
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:
Joined: Sat Jul 11, 2009 10:29 am Posts: 928 Location: USA
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.
Joined: Thu Dec 13, 2007 3:42 pm Posts: 4091 Location: the Netherlands
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.
Joined: Thu Dec 13, 2007 3:42 pm Posts: 4091 Location: the Netherlands
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.
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.
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.
Joined: Thu Dec 13, 2007 3:42 pm Posts: 4091 Location: the Netherlands
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)
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.
Joined: Tue Nov 04, 2008 11:59 pm Posts: 160 Location: Hong Kong
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 !
Joined: Tue Oct 17, 2006 11:33 am Posts: 403 Location: New Zealand
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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