The Opal Bed in Malheur County, Oregon, is a well-regarded thunderegg site known for producing nodules with vibrant common opal and agate interiors. Eggs from this bed often feature bright, glassy opal in shades of white, cream, yellow, or even pale green, sometimes mixed with chalcedony or quartz. Some specimens display subtle banding or mossy inclusions, while others are nearly solid opal—offering excellent material for cabbing and display. The rhyolite matrix is typically light and porous, making extraction easier compared to harder beds. Collectors and lapidaries value Opal Bed thundereggs for their color variety, smooth cutting properties, and eye-catching polish.
Rocks of the Cascades – Thundereggs, Tools & Tradition