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Sunstone Plagioclase Feldspar from Ethiopia

Sun, Ziyin and Renfro, Nathan D. and Palke, Aaron C. and Breitzmann, Heidi and Muyal, Jonathan and Hand, Dylan and Hain, Maxwell and McClure, Shane F. and Katsurada, Yusuke and Miura, Makoto and Rossman, George R. (2020) Sunstone Plagioclase Feldspar from Ethiopia. Gems and Gemology, 56 (1). pp. 184-188. ISSN 0016-626X.

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Ethiopia, traditionally known for opal, has become an important source for emerald and sapphire. After these significant discoveries, a new type of Cu-bearing sunstone feldspar, first shown in 2015 to Tewodros Sintayehu (Orbit Ethiopia Plc.), was discovered in the Afar region (L. Kiefert et al., “Sunstone labradorite-bytownite from Ethiopia,” Journal of Gemmology, Vol. 36, No. 8, 2019, pp. 694–695). This material made its way to the jewelry market last year in Tucson. To fully characterize this new production, GIA obtained 48 Ethiopian sunstones for scientific examination. Among them, 44 rough stones (figure 1, left) were borrowed from Stephen Challener (Angry Turtle Jewelry), who acquired them from an Ethiopian gem dealer in Tucson in February 2019. Another four rough stones (figure 1, right) were purchased by author YK from Amde Zewdalem (Ethiopian Opal and Minerals) and Benyam Mengistu, who facilitates mining and exporting samples from Ethiopia, at the Tokyo International Mineral Association show in June 2019. Prior to this discovery, the only verified occurrences of Cu-bearing feldspar were from Lake and Harney Counties in Oregon (e.g., the Dust Devil and Ponderosa mines). However, more than a decade ago there was a controversy about Cu-bearing feldspar on the market purportedly from Asia or Africa with an undetermined color origin, presumably Cu-diffused (G.R. Rossman, “The Chinese red feldspar controversy: Chronology of research through July 2009,” Spring 2011 G&G, pp. 16–30; A. Abduriyim et al., “Research on gem feldspar from the Shigatse region of Tibet,” Summer 2011 G&G, pp. 167–180). Gemological testing and advanced analytical methods helped distinguish this new Ethiopian material from the Oregon material and the controversial feldspar of questionable color origin mentioned above in order to ensure GIA’s accurate reporting of the natural origin of Cu-bearing feldspar.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 2020 Gemological Institute of America.
Issue or Number:1
Record Number:CaltechAUTHORS:20201130-072850026
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106837
Deposited By: Tony Diaz
Deposited On:02 Dec 2020 20:24
Last Modified:02 Dec 2020 20:24

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