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 Post subject: Color-change Garnets
PostPosted: Sat Nov 07, 2020 11:37 am 
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I used to buy a lot of gems from Zimbabwe, mostly Sandawana emeralds and aquamarine, tourmaline and alexandrite
To keep the supplier/cutter happy, I would usually take everything in the parcel, including "rhodolite", hessonite etc.At some point I examined the "rhodolite" with a penlight and noticed it changed from red garnet to amethyst purple.After some research, I found an article in GIA about color-change garnets from Tanzania.This stuff looks like the stones in the article, supposedly from material mined in the 1980's.I couldn't find out where my garnets had come from, as the cutter had died, but he did source parcels from all over Southern/East Africa.Anyway, sorry for the long-winded story, but am hoping one of you can indicate if there is a market for this as I have thousands of carats of it.In the GIA article, a guy called Todd Wacks was trying to market it, but I don't think anyone here[South Africa] knows it, let alone being prepared to buy it.


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 Post subject: Re: Color-change Garnets
PostPosted: Sat Nov 07, 2020 11:42 am 
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Sounds like the typical color shift in rhodolite garnets. A true color change garnet will be from some shade of green/blue to red/purple.


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 Post subject: Re: Color-change Garnets
PostPosted: Sat Nov 07, 2020 2:47 pm 
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Yeah, pretty much any rhodolite will do this to some ectent. Presumably they have a mix of unshifting red and of red/blue color change, which presents as a red/purple change. That said, most stones in this color range (ie amethyst) will do this to some extent anyway.

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 Post subject: Re: Color-change Garnets
PostPosted: Sun Nov 08, 2020 10:43 am 
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Thanks for the tips.When I saw them, I thought they were colour shift rather than colour change.However, the GIA article refers to them as color-change and, assuming they knew more than I do, I will take their word for it.They were claimed to be a new type of garnet consisting of 80%pyrope,10% spessartine and 10% almandine.They are really quite beautiful
PS-I sent some to Ed at Wildfish gems who had them checked out.The German DSEF classified one as colour-shift while IGI referred to them as colour-change.With Ed's usual good photography, you can see the changes in the 1.37ct specimen on the Wildfish Gems website.


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 Post subject: Re: Color-change Garnets
PostPosted: Sun Nov 08, 2020 11:33 am 
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Is it this same material that Tucson Todd sells? I have seen and spoken to him about these stones. He claims he has the only supply of them. You may want to get in contact with him about value.

A well equipped lab should easily be able to determine the end member garnet component mix to confirm that they are the same.


https://www.tucsontoddsgems.com/color-change-pyrope/


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 Post subject: Re: Color-change Garnets
PostPosted: Sun Nov 08, 2020 3:38 pm 
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The "pastel pyrope" stuff the GIA wrote about seems to be pretty much a light toned rhodolite with a pronounced color shift. I am not even convinced it is really unudually pronounced, as the effect is very strong on plenty of random rhodolites. Presumably the more pyrope-leaning base and different proportions of colorants have some effect, but I don't think there's anything fundamentally different about this material, and I doubt it's even outside the normal range of variations from a number of finds. That being said I love Tucson Todd's goods and enjoy looking at his stuff whenever I'm in Tucson.

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 Post subject: Re: Color-change Garnets
PostPosted: Mon Nov 09, 2020 12:24 pm 
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Hi Ibwana Thanks, it is the same stuff he sells[at least looks like it]He is in a video on the GIA article. I will try and get hold of him-he looks very approachable in the video.This stuff is also from Tanzania, but I don't know the location.


Last edited by raygem on Mon Nov 09, 2020 12:30 pm, edited 1 time in total.

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 Post subject: Re: Color-change Garnets
PostPosted: Mon Nov 09, 2020 12:27 pm 
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Thanks Stephen.The change is very pronounced, as in the photos on Wildfish gems [the 1.37ct and a few others from the same source]


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