Hi all. A new member here but this topic caught my attention as I have a crystal fragment of this feldspar, bought about 7 years ago from a mainstream crystals shop in Salisbury. It's about 39 mm by 25 mm and about 17 mm thick, and weighs about 25 grams. Photos below:
It shows clear pleochroism from a yellowish-green to a more bluish-green as the crystal is turned, and is dramatic using the polarising effect of an LCD monitor. From what I have gathered it is from southern Tanzania, or just over the border in Kenya. I have not seen anything like it for sale since, either in the 'rock shops' or the Kempton Park gem shows. Certainly a beautiful specimen!
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21602 Location: San Francisco
Nick. I approved your message BUT your pictures are far too large for our format. They distort our pages. The recommended picture width is 600px. Your are 4,288px × 3,216px!
If you want to see what it does to our pages, try replying to this message. I will resize your pictures eventually, but, in the future, PLEASE do not post anything larger than 600px. Thanks.
Nick. I approved your message BUT your pictures are far too large for our format. They distort our pages. The recommended picture width is 600px. Your are 4,288px × 3,216px!
If you want to see what it does to our pages, try replying to this message. I will resize your pictures eventually, but, in the future, PLEASE do not post anything larger than 600px. Thanks.
Sorry Barbra. I can change the links to smaller versions if you like.
Yup, that's the classic 'green sunstone' from Tanzania (or the area). I got some smaller pieces on eBay, mostly cab grade but some for faceting (along with some of the super nice golden star sunstones that were produced around the same area, maybe the same time too). I think it's awesome material, though mostly not that valuable. A few of the golden ones have 8-ray stars though which are pretty cool.
Corona makes it possible for me to deal with my hobby more intensively again after a long time. After there have been intensive discussions here, I hope I can contribute to the clarification. I had the stone examined by the German Foundation for Gemstone Research (DSEF). Enclosed the certificate. I have translated the second page.
"We have carried out both chemical and various spectroscopic (UV/VIS, FTIR, RAman) investigations on the feldspar material described in the above-mentioned findings report of 21.04.2020. This is an orthoclase (potash feldspar) with the general chemical formula KAlSi3O8. Furthermore, traces of lead (Pb) and structurally bound water (H2O) could be detected. It is known that Pb and H2O in potash feldspars form precursors of colour centres which are activated by electromagnetic radiation and lead to the green to green-blue shades typical of the Amazonite variety."
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