Gems & Gemology, Summer 2010, Volume 46, No. 2

Play-of-Color Opal from Wegel Tena, Wollo Province, Ethiopia

Peer Reviewed Article
Benjamin Rondeau, Emmanuel Fritsch, Francesco Mazzero, Jean-Pierre Gauthier, Bénédicte Cenki-Tok, Eyassu Bekele, and Eloïse Gaillou
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Play-of-Color Opal from Wegel Tena, Wollo Province, Ethiopia

A new opal deposit was discovered in 2008 near the village of Wegel Tena, in volcanic rocks of Ethiopia’s Wollo Province. Unlike previous Ethiopian opals, the new material is mostly white, with some brown opal, fire opal, and colorless “crystal” opal. Some of it resembles Australian and Brazilian sedimentary opals, with play-of-color that is often very vivid. However, its properties are consistent with those of opal-CT and most volcanic opals. Inclusions consist of pyrite, bariummanganese oxides, and native carbon. Some samples show “digit patterns”: interpenetrating playof-color and common opal, resembling fingers. The opaque-to-translucent Wegel Tena opals become transparent when soaked in water, showing a remarkable hydrophane character. White opals from this deposit contain an elevated Ba content, which has not been reported so far in opal-CT. The fire and crystal opals are prone to breakage, while the white, opaque-to-translucent opals are remarkably durable. The proportion of gem-quality material in the Wegel Tena deposit seems unusually high, and 1,500 kg have already been extracted using rudimentary mining techniques. The deposit may extend over several kilometers and could become a major source of gem-quality opal.


Details of the LA-ICP-MS Analytical Conditions 
Chemical Composition of Opals from Wegel Tena, Ethiopia, Measured by LA-ICP-MS
July 31, 2010

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