Oregon Opal

Oregon opal refers to several distinct opals mined in the state of Oregon, USA. The best known are Owyhee blue opal, a soft translucent blue common opal, and the precious opal from Opal Butte in the Blue Mountains, which can show vivid contra-luz play-of-color in a clear or pink body.

Oregon also produces fire opal in warm orange tones. The variety and quality of these opals have made Oregon one of the more notable opal-producing regions in North America.

Many Oregon opals are faceted because of their transparency, and the state's precious opal is prized by collectors.

Oregon opals form in the region's extensive Tertiary volcanic rocks. Owyhee blue opal occurs as seams and nodules in volcanic ash and rhyolite in the Owyhee area near the Oregon-Idaho border, deposited from silica-rich groundwater.

The famous Opal Butte precious opal forms inside hollow rhyolite "thunderegg" nodules, where opal lined or filled gas cavities in the lava. Slow, low-temperature silica deposition produced both common and precious varieties.

The blue color is generally attributed to fine silica/light scattering and trace elements, while orange fire opal owes its color to iron oxides.

Look for translucent blue (Owyhee), clear, pink, or orange opal with a vitreous luster, white streak, and Mohs hardness near 5.5-6.5. Precious Opal Butte material shows play-of-color, often best seen with light passing through (contra-luz).

Look-alikes: Chalcedony and quartz are harder (7) and crystalline. Larimar and Peruvian blue opal are similar in color to Owyhee but come from elsewhere; Owyhee is often more uniformly pale blue. Some Oregon opal is hydrophane and may absorb water.

Lower hardness than quartz and possible crazing help confirm opal identity.

Oregon opal is cut into cabochons (Owyhee blue) and faceted gems (clear and precious Opal Butte material) for jewelry, and is sought by collectors of American gemstones. Owyhee blue opal is popular in artisan silver jewelry.

Some Oregon opal, being hydrophane or water-sensitive, should be kept dry and away from oils and chemicals, and protected from impact and dehydration.

Oregon opal is significant as a domestic U.S. gem source and is associated with the state's rich rockhounding tradition (Oregon's official gemstone is the sunstone, a separate material).