Owyhee Opal
Owyhee Opal
Common and rare precious opal from the high Oregon desert
Owyhee opal is the trade name for opal from the Owyhee region of the Oregon-Idaho-Nevada borderlands, the same volcanic terrane that produces the Owyhee jaspers and Oregon's better-known Mexican-style fire opal. The Owyhee material includes both common opal — opaque to translucent, blue, pink, brown, or multicoloured, traded principally as Oregon blue opal in the case of the most distinctive variety — and occasional precious opal with play-of-colour. The deposits were brought into commercial production in the early 2000s and have established a presence in the cabochon and beadwork market.
Geological setting
The Owyhee opal deposits formed in the silicic volcanic flows and tuffaceous sediments of the Miocene Owyhee volcanic episode, with opal precipitated from silica-saturated meteoric and hydrothermal fluids in vughs, fractures, and along bedding planes. The geological setting is broadly comparable to the volcanic-hosted opal deposits of central Mexico and Honduras and is distinct from the sedimentary opal deposits of central Australia. The most active workings are in southwestern Idaho and adjacent eastern Oregon.
The blue Owyhee material
The most distinctive Owyhee opal is a translucent to semi-translucent material with a soft blue to blue-green body colour, traded under the name Owyhee blue opal or Oregon blue opal. The colour is structural rather than pigmentary, arising from light scattering at the boundaries of the silica-sphere assembly that forms the opal matrix, and the body shows a characteristic milky to slightly glassy quality in directly transmitted light. Cabochons of the material can be very attractive, particularly with the soft pearlescent quality the material develops on a high polish.
The blue Owyhee opal generally lacks the play-of-colour of fine precious opal but is valued for its body colour and translucency. It is most often cut as cabochon and as faceted material; the latter is unusual among common opals because the Owyhee blue is sufficiently transparent in the better-grade rough to reward a faceted cut.
Pink and multicoloured Owyhee material
Pink common opal from the Owyhee deposits, sometimes traded as Owyhee pink opal, is generally less translucent than the blue variety and shows a soft mauve-pink to peach body colour. Multicoloured material with brown, white, and pink banding is also produced, often resembling a cross between common opal and chalcedony. A small fraction of the Owyhee output shows play-of-colour and is sold as precious Owyhee opal, with green and orange flashes typical; the play-of-colour material is generally smaller and less stable than the precious opal of central Mexico or Australia.
Stability and care
Common opal in general is more stable than precious opal, but the volcanic-hosted Owyhee material can be sensitive to dehydration and to thermal shock, particularly the play-of-colour material. The blue Owyhee opal is the most stable of the Owyhee varieties and is generally considered safe for routine wear in protected settings. Buyers should expect dealer disclosure of any stabilisation or impregnation treatment; the latter is occasionally applied to the more porous Owyhee material to improve durability and is detectable by laboratory analysis.
Cleansing should be by mild soap and warm water with a soft cloth; ultrasonic and steam cleaning are not recommended. Storage in a humidity-stable environment helps preserve the long-term stability of the material.
In the trade
Owyhee opal is a niche material in the international trade but has built a steady commercial presence through the western United States gem-show circuit and through specialist dealers in cabochon and bead production. The material is most often encountered in the Tucson, Quartzsite, and Denver shows and through online specialty dealers. Pricing is moderate, with the better-grade Owyhee blue cabochons priced in the low to mid double-digit dollar-per-carat range and the play-of-colour material commanding higher prices for the small fraction of the output that achieves it.