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 Post subject: Harts Range zircon fading in sunlight
PostPosted: Fri Apr 12, 2013 5:57 pm 
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Location: Rubyvale
I have some beautiful Harts Range zircon of varying colours. Strong pink, plums, oranges etc. However, these stones will often change colour slightly when hot dopping, so I now cold dop them. Unfortunately, after a couple hours out in the sun (in central Qld, quite strong!) they fade significantly. Pinks become almost white, plums, red/orange will become a pale orange/pink colour. Most colours end up pale champagne/orange/pink, or near white.

When I first noticed this, the possibility of these stones being tenebrescent was suggested (another reason that I cold dop, as heat can destroy tenebrescent effect). A dark port coloured (kind of burgundy) stone faded to a pale pink/orange. I have had in in a dark place for 6 months. In the first few weeks it seemed to start to 'come back' to it's original colour. It has not changed since then, and is now a pale pinky/orange/mauve colour. Very pretty, but no where near it's original colour.

Is this still tenebresence? Or some other phenomenon? It is possible that these stones have
never been exposed to uv light. Does the long wave uv light permanently affect the crystal lattice? Applying short wave uv light does not help. My problem is now that I have some more beautiful coloured HR zircon, and want to be able to have them retain their 'original' colour, and not fade. Is there any way of doing this? (Apart from keeping them in the dark). This is also an issue when getting these stones valued and trying to sell them, as the colour will change from the original valuation. Any advise would be appreciated. Thank you.


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 Post subject: Re: Harts Range zircon fading in sunlight
PostPosted: Sun Apr 14, 2013 5:52 pm 
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Quote:
Is this still tenebresence?
My problem is now that I have some more beautiful coloured HR zircon, and want to be able to have them retain their 'original' colour, and not fade. Is there any way of doing this?

sorry but no to both questions, the Hearts Range Zircons change their colors once exposed to UV and are not stable , speaking color wise. Even once heated they can still change.
This is just the nature of Zircon, depending of region and metamization state of the Zircon.
By the way I think Hearts Range has the best pinks in the world.

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 Post subject: Re: Harts Range zircon fading in sunlight
PostPosted: Mon Apr 15, 2013 5:16 pm 
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Thank you for that reply, much appreciated. A bit disappointing though to know that to keep theses stones at their original colour, I will have to put them in a box or only wear at night. :( Yes the pinks and mauve's are beautiful. Have to keep them out of the sun though I guess. I believe that the Hart's Range zircon are non-metamict (as they do not contain any uranium or thorium). One of the reasons they are so brilliant. :)

So then the colour fading, and then changing again after being in the dark is a result of the instability of the crystal lattice, crystal structure (is that the same thing?) It would be interesting to understand exactly what is happening in these stones, on a scientific level. Can anyone explain this please?


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 Post subject: Re: Harts Range zircon fading in sunlight
PostPosted: Tue Apr 16, 2013 5:18 am 
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Hi Cindy,

Cool to see you on GemologyOnline, how's it going?

cindyjkelly wrote:
So then the colour fading, and then changing again after being in the dark is a result of the instability of the crystal lattice, crystal structure (is that the same thing?) It would be interesting to understand exactly what is happening in these stones, on a scientific level. Can anyone explain this please?


More info on the effect can be found here. This page builds on top of this information which should be read as well in order to be able to put things in perspective.

All the best,

Tim


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 Post subject: Re: Harts Range zircon fading in sunlight
PostPosted: Tue Apr 16, 2013 5:27 pm 
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Thank you very much for your response Tim. That information is helpful and exactly what I was after. May need to do a bit more research to completely understand it, but am off to a good start. :)


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 Post subject: Re: Harts Range zircon fading in sunlight
PostPosted: Tue Apr 16, 2013 5:44 pm 
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Hi Cindy

Zircons are allochromatic their color is due to defects in the lattice and or trace element. Further the Hearts Range Zircons contain Uranium but just not enough ppm to be classified as metamic.
The whole color change happening in zircons is not yet fully understood mainly due to the complexety of the whole rare earth trace elements.
By the way Welcome Cindy, we know each other from the fields. Its Swiss Oliver here.

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