Oregon Opal — Common and Precious Material from American High-Desert Volcanic Country
Oregon Opal — Common and Precious Material from American High-Desert Volcanic Country
A minor opal source most often encountered as a by-product of sunstone mining or as Owyhee blue and pink material
Oregon opal is the umbrella trade term for opal produced in the volcanic terrains of central, eastern, and southeastern Oregon, including the Owyhee district that straddles the Oregon-Idaho border. The state's opal output is small by international standards and is best understood as several distinct deposits with different characteristics, ranging from common opal of various colours to occasional precious opal with play-of-colour and to the contra-luz fire opal occasionally found as inclusion within Plush sunstone. Oregon opal has not displaced Australian or Ethiopian material in volume, but specific deposits have produced gem-quality stones that trade at recognisable prices in specialist channels.
Sources and varieties
The most commercially important Oregon opal source is the Owyhee district, where blue and pink common opal is produced in rhyolitic volcanic flows. Owyhee blue opal, the best-known of these materials, is a translucent to semitransparent stone with body colour ranging from pale to deep blue-grey, sometimes marketed as Oregon blue opal or under variants of that name. Pink Owyhee opal of similar character is produced from the same district, and small amounts of multicoloured common opal also appear. The colour in these stones is body colour rather than play-of-colour; the material does not show the spectral diffraction effect of precious opal.
Opal Butte, in the Blue Mountains of Morrow County in eastern Oregon, has produced precious opal with play-of-colour from rhyolitic host rock. Production has been intermittent and limited since the deposit's working in the 1990s, but Opal Butte material with strong play-of-colour against pale blue or grey body has reached the cutting market and traded at prices comparable to second-tier Australian boulder material.
The third significant Oregon opal occurrence is as inclusions and intergrowths in Plush sunstone, where small amounts of fire opal and contra-luz fire opal are found in the host basalt and within the sunstone phenocrysts themselves. This material is rarely cut as a primary gem and is typically encountered only in cutters' working stocks.
Stability and care
Oregon volcanic-host opal varies in stability. The Owyhee blue and pink material is generally more stable than some Australian potch and Ethiopian Welo opal but is still hydrated silica and benefits from conservative handling. Avoid prolonged dry-environment storage, sudden temperature change, and ultrasonic cleaning. Care recommendations are conservative across the board for opal regardless of locality.
In the trade
Oregon opal trades primarily with American lapidaries and specialist dealers rather than at international scale. Owyhee blue opal has built a niche market for its colour, and Opal Butte material when available is collected by precious-opal specialists for its locality and its competent play-of-colour. The material is rarely encountered in commercial fine-jewellery channels and is most often set in artist or studio jewellery. See also Owyhee opal, Opal Butte, Oregon sunstone.