August 31-September3—RALEIGH, NORTH CAROLINA: Annual show; Treasures of the Earth, Inc.; NC State Fairgrounds; Fri. 12-6, Sat. 10-5, Sun. 10-5, Mon. 10-4;
Welcome to the Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Mon Aug 20, 2018 12:38 am

All times are UTC - 4 hours

Post new topic Reply to topic  [ 2 posts ] 
Author Message
 Post subject: Microworld of Gems: New Sunstone from North Carolina
PostPosted: Wed Feb 07, 2018 5:42 pm 
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 2895
Location: North Carolina
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! ... 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:

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!

Reply with quote  
 Post subject: Re: Microworld of Gems: New Sunstone from North Carolina
PostPosted: Wed Feb 07, 2018 7:31 pm 
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 18885
Location: San Francisco
Bravo Stephen!
That is awesome!

Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 2 posts ] 

All times are UTC - 4 hours

Who is online

Users browsing this forum: No registered users and 1 guest

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock