Novembr 16-18—COLUMBIA, SOUTH CAROLINA: Annual show; The Columbia, SC Gem and Mineral Society; Fri. 10-6, Sat. 10-6, Sun. 12-5
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 Post subject: Microworld of Gems: New Sunstone from North Carolina
PostPosted: Wed Feb 07, 2018 5:42 pm 
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This is my first foray into to the gemological literature, made possible by the incomparable Nathan Renfro and Ziyin Sun at the GIA. Thanks again to both of you for sharing your incredible resources and letting me come along on the ride!
https://www.gia.edu/gems-gemology/winte ... inclusions
This was a very fun project, and beyond the publication it's still ongoing. A prospector (Ryan Underwood) had come to one of our local gem shows in Raleigh and was showing off material to a good friend of ours who referred him to me. Most people had told him it was just moonstone or plain feldspar, but he knew otherwise and left a couple of specimens. At first glance I thought the same, that they were just three roughly shaped pieces of tan or grey feldspar, but when I turned them in my hand I suddenly saw a nice bright irridescent flash. Closer inspection showed it had nice presumably hematite platelets similar to what you would see in African sunstone with a very attractive appearance.

I thought that was neat and got in touch with Ryan, who had done a lot of footwork on his own to figure out what he had. He'd also found an old reference to sunstone having been found in the area in a rockhounding guide, and some further tracking revealed a reference in Kunz's "Gems and Precious Stones of North America" (1890), which I can reproduce here since it's long out of copyright:
Image

So, this material was sort of known, but then Ryan showed me pictures of something even more intriguing--some of the stones showed a lattice pattern similar to Australian rainbow lattice. I ended up going out to meet him and see the deposit and he showed me several specimens. As with the Australian material you get normal polygonal irridescent flakes of varying size from two or three orientations, but one orientation shows platelets that are significantly elongated and often arrange themselves into a lattice-like pattern. From reading through the very sparse references to this material it's unclear if the stones they found back in the 1800s didn't show this pattern or if they just cut them to show the more obvious specks. The other wrinkle is that the older material was found some distance from the new material, and was consistently reported as oligoclase while this material is obviously a potassium feldspar in the hand (confirmed by LA-ICP-MS). It's hard to tell with gemological/geological publications from that period since the methodology was so different back then.

There's also a nice range of base colors, including typical tans and greys and also a red-pink apparently caused by further fine inclusions of hematite. Perhaps unlike the Australian material this stuff is in a metamorphic biotite gneiss, likely remnants from a source granite that have taken a real beating. They are found either as larger pods or as individual grains smooshed within this host rock. As such there are significant difficulties in finding clean material and cutting large stones, but every now and then they recover some more solid stuff. Clarity is also generally lower than the Australian though some clear stones do come out. I don't know what the future of this material will be but it's fairly cool stuff, and also nice to reintroduce a forgotten NC classic with a new twist.

I sent a few samples to Nathan and he took these amazing pictures, did some analysis with Ziyin Sun and got this note together. This was a tremendously fun process so I'm hoping I'll find some other interesting things to send him!


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 Post subject: Re: Microworld of Gems: New Sunstone from North Carolina
PostPosted: Wed Feb 07, 2018 7:31 pm 
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Bravo Stephen!
That is awesome!


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 Post subject: Re: Microworld of Gems: New Sunstone from North Carolina
PostPosted: Fri Nov 02, 2018 2:33 pm 
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This is fantastic! I read this once before, but I still wanted to stop back in and say .."awesome"!
Check out this recent hand dug specimen from North Carolina, that my good buddy Jimmy found at one of his quartz crystal locations.. It's one of 2 or 3 he found with some blue type mineral.
https://www.facebook.com/ReelMiner/videos/1980065002308439/

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 Post subject: Re: Microworld of Gems: New Sunstone from North Carolina
PostPosted: Fri Nov 02, 2018 3:25 pm 
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Wow! Has he had it looked at yet? I'd love to get it under the scope/raman.


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