gems, opal, Ethiopia

A new source of high-quality play-of-color opal was discovered in early 2008 in Welo Province, Ethiopia, approximately 500 km north of Addis Ababa, and is geographically distinct from the earlier Mezezo deposit in Shewa Province. A parcel of five rough and 30 cut Welo opals examined by contributors from Opalinda and Eyaopal revealed cabochons with good play-of-color, mostly white and transparent, though some exhibited light yellow to dark brown bodycolor. Compared to Mezezo opals, Welo specimens appeared whiter and showed all spectral colors in their play-of-color, with most resembling opals from Australia or Brazil. Many samples also displayed a columnar structure of play-of-color opal within common opal—rare outside Ethiopia. Specific gravity ranged from 1.80 to 2.10, influenced by high porosity, as seen in up to 8% weight increase after water immersion. Fluorescence ranged from inert to moderate yellowish white under UV; some inert samples phosphoresced greenish, while yellow-to-brown opals showed no luminescence, likely due to iron. Yellow-to-green luminescence may be due to uranium. Fourier-transform Raman spectra confirmed opal-CT with characteristic bands at ~1070, 780, 670, and 345 cm⁻¹, and water bands near 3200 and 2950 cm⁻¹. Welo opal occurs in volcanic rock—likely rhyolite—cementing fragments of the host, unlike Mezezo opals which fill cavities as nodules; the shared columnar textures, however, suggest similar formation conditions.