Sun Z, Renfro ND, Palke AC, Breitzmann H, Muyal J,,Hand D, Hain M, McClure SF1, Katsurada Y. Miura M2,
George R. Rossman3,
1Gemological Institute of America, Carlsbad, CA, USA
2Gemological Institute of America, Tokyo, Japan
3Division
of Geological and Planetary Sciences, California Institute of
Technology,
Pasadena, California 91125, USA
ABSTRACT
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.