Shewa Opal — Ethiopian Volcanic Opal from the 2008 Discovery
Shewa Opal — Ethiopian Volcanic Opal from the 2008 Discovery
White and crystal opal from rhyolitic deposits in central Ethiopia
Shewa opal, also rendered Shoa opal in some sources, is precious opal from the Shewa (Shoa) Province of central Ethiopia, discovered in 2008 and produced commercially since around 2010. The material is predominantly white to crystal body type, displaying vivid play-of-colour that often manifests as broad flash patterns rather than the more pinpoint patterns common in Australian sedimentary opal. Shewa opal occurs in volcanic rhyolite host rock, in a deposit type that is geologically distinct from the older Welo opal deposits in northern Ethiopia and from the dominant Australian sedimentary deposits in mainland Australia.
Discovery and production
Opal had been known from various Ethiopian localities since the 1990s, with the major Welo (Wollo, Wolo) field in the Tsehay Mewcha area of northern Ethiopia attracting international attention from around 2008. The Shewa deposits were identified during the same period of expanded prospecting activity in the country and have been worked commercially since approximately 2010. Production has been variable, with periods of active mining alternating with quieter periods, but the deposits have established Shewa as one of several distinct Ethiopian opal sources contributing to the international market.
Mining at Shewa is typically small-scale and artisanal rather than large-scale commercial. The opal occurs in nodules and seams within rhyolitic volcanic rock, and miners work the deposits by hand and small mechanised equipment. Production volumes are not well documented in the public trade press, but the material reaches international markets primarily through Ethiopian and Hong Kong dealer networks.
Body type and play-of-colour
Shewa opal is predominantly white to crystal in body type — meaning the body of the stone ranges from translucent white to fully transparent — with the play-of-colour displayed against this light ground. The pattern is often a broad flash of strong colour across the stone, sometimes with multiple colour zones visible from different viewing angles. Red and orange flash on a white ground is the most highly valued pattern; green, blue, and yellow flashes are more common.
Crystal-bodied Shewa material — fully transparent in the body — shows the play-of-colour with particular clarity, since the colour is not muted by background opacity. Such stones approach the optical character of fine Australian crystal opal and command relatively high prices for the better examples.
Stability and the question of crazing
Ethiopian volcanic opals from various deposits, including Shewa and Welo, have a documented hydrophane character: the stone absorbs water when soaked and releases it when dried, with associated changes in transparency and colour. This hydrophane behaviour distinguishes volcanic Ethiopian opal from Australian sedimentary opal, which is generally not hydrophane.
The hydrophane behaviour is a stability concern in two respects. First, water absorption can temporarily mask the play-of-colour, making the stone appear duller until it dries. Second, repeated wet-dry cycling has been associated in some Ethiopian opals with development of crazing — fine network cracks that compromise transparency and beauty. Trade reports through the 2010s on Welo opal flagged crazing as a recurring concern with that source. Shewa material has been described in some trade reports as more stable than Welo with respect to crazing risk, though comparative data are not consistent across sources, and individual stones from any volcanic Ethiopian deposit should be assessed for stability rather than assumed to behave uniformly. Reputable dealers will hold Shewa stones through controlled humidity cycles before sale to verify stability.
Treatment
Some Ethiopian opal, including material from various deposits, has been observed in laboratory and trade testing to have been treated with smoke (smoke treatment), with sugar-and-acid darkening, with polymer impregnation, or with other procedures intended to modify body colour or improve apparent play-of-colour. Disclosure of treatment is required under FTC and CIBJO trade rules. Buyers should request laboratory characterisation for any significant Ethiopian opal purchase to verify untreated status.
Cutting and use
Shewa opal is cut almost exclusively as cabochons, with shape and dome contour optimised to display the play-of-colour pattern. Faceted opal is rare and is generally reserved for transparent material with strong dispersion, where the gem behaves more like a faceted-stone than a play-of-colour stone. Hardness is approximately 5.5 to 6.5 on the Mohs scale, modest by jewellery-stone standards, and the stone is sensitive to impact, thermal shock, and chemical attack.
Setting recommendations follow the general guidance for opal: bezel or protective prong settings rather than exposed prong settings, particularly for ring applications; pendants and earrings are easier choices for daily wear. Cleansing should be by mild soap and warm water; ultrasonic and steam cleaning should not be used. Storage in a soft pouch or compartmented box, away from harder gems and from direct heat, supports long-term stability.
In the trade
Shewa opal occupies a mid-market tier in the international opal trade, competing on a price-and-quality basis with Australian white and crystal opal. The Ethiopian deposits as a whole have substantially altered the global opal supply over the 2010s, with significant volumes of fine-quality material reaching markets at prices well below comparable Australian production. Shewa material specifically is less well known in the trade than Welo, but has carved a recognisable niche through its body-type characteristics and reported relative stability advantages over the better-known northern Ethiopian source.