Oregon’s unique geological history, shaped by immense volcanic activity and ancient lava flows, has created one of the most rewarding environments for gemstone discovery in the United States. The varied landscape, from coastal beaches to high desert plateaus, is rich with diverse mineral deposits. This abundance results from millions of years of geothermal processes, where mineral-rich water infiltrated voids in volcanic rock. The gems found here, including the state’s official gemstone and rock, attract enthusiasts from around the world.
Oregon Sunstone and Other Feldspar Gems
The state gemstone, the Oregon Sunstone, is a variety of plagioclase feldspar. This gem formed approximately 15 million years ago in basaltic lava flows, primarily in the high desert regions of Harney and Lake counties. The sunstone’s most celebrated feature is an internal sparkle called aventurescence, or schiller, caused by microscopic platelets of pure copper suspended within the crystal structure. These copper inclusions reflect light, producing a glittering effect and a range of natural colors, including pale yellow, salmon pink, red, and rare blue-green hues. The concentration of copper determines the depth of color. The primary collecting area is the remote Rabbit Basin near Plush, Oregon, where the gem is often found loose in weathered basalt.
Thundereggs and Geode Formations
The Thunderegg, designated as Oregon’s state rock, is a nodule-like formation created within rhyolitic volcanic ash layers or silica-rich lava flows. These spherical structures begin as gas pockets within the lava that cool and harden. Over time, mineral-laden groundwater seeps into the voids and deposits layers of silica. A Thunderegg is a specific volcanic structure that is usually completely or mostly filled with material, though it may contain a hollow center and thus also qualify as a geode. The interiors of these nodules reveal centers of material, often displaying intricate patterns and vibrant colors:
- Chalcedony.
- Agate.
- Jasper.
- Common opal.
Thundereggs are abundant across Central and Eastern Oregon, with significant deposits found in areas like Crook, Jefferson, and Wasco counties.
Common Agates, Jaspers, and Petrified Wood
Oregon is a world-class source for quartz-based materials found throughout the state, from the coast to the high desert. Agates are particularly plentiful along the Pacific coastline, polished smooth by wave action. Coastal finds often include banded agate, carnelian, and rare enhydros (nodules containing trapped water).
Inland, Eastern Oregon is known for specialized types of agates, such as the highly sought-after plume agate, which features inclusions resembling feathers or flowers. Notable varieties include Graveyard Point Plume and Priday Plume, the latter often found encased within Thundereggs. Jaspers, an opaque form of chalcedony, occur in a wide color spectrum. Picture Jasper from areas like Biggs Junction displays scenic landscape patterns in brown, tan, and cream.
Petrified wood is also a common find, resulting from ancient forests being mineralized by silica-rich water. This process replaces the organic wood structure with quartz, preserving the tree’s grain and ring structure. Excellent examples are found near Sweet Home and the Hampton Butte area, known for its rare green petrified wood. Common opal is frequently discovered alongside these agates and jaspers, often appearing as a translucent filling or coating.
Public Collecting Sites and Regulations
Rockhounding is permitted across vast tracts of Oregon’s public lands, but collectors must adhere to regulations set by the managing agencies. The Bureau of Land Management (BLM) oversees most high-desert collecting areas, including the Oregon Sunstone Public Collection Area near Plush. Visitors may collect sunstones here for personal, non-commercial use at no charge, though private mines near Plush offer “fee-dig” opportunities for higher-quality stones.
On general BLM land, the collection limit for personal use is 25 pounds plus one piece per day, with a yearly maximum of 250 pounds. Collection is restricted to non-motorized tools, such as shovels, picks, and screens. Regulations on the Oregon Coast are stricter, limiting the collection of non-living items like agates to one gallon per person per day and three gallons per year.
Ethical collecting practices are important to preserve the environment. Collectors must always fill in any holes they dig and should avoid disturbing active mining claims or private property without explicit permission. The collection of vertebrate fossils and cultural artifacts like arrowheads is strictly prohibited on all public lands.