What is a thunderegg? On the outside, thundereggs look like ordinary rocks. Their rough exteriors are unremarkable. However, their internal surprise makes them quite remarkable. On the inside, this state rock of Oregon holds a beautiful array of colors and patterns from swirling lines to geometric patterns and more.
How are Thundereggs Formed?
Thundereggs are formed when the voids in rhyolitic lava flows and tuffs are filled with mineral-rich hydrothermal fluids. Over time these fluids solidify and crystallize filling the interior with minerals such as agate, chalcedony, opal and jasper. The different colors inside are formed because of the minerals in the intruding solution. The solutions can vary from location to location because of the differences in the local soil and rock where they percolate.
Most thundereggs are baseball to softball size but can be as tiny as a few centimeters or as large as a few feet in diameter. While thundereggs most often have a solid interior, sometimes they can have a central cavity that does not solidify and visible crystals can form. These are sometimes called “geode thundereggs.”
Where to Find Thundereggs
Richard Gross
Thundereggs can be found around the world. Oregon is famous for its thundereggs, especially in Crook, Jefferson, Malheur, Wasco and Wheeler counties. They are also found in Australia, Brazil, Canada, Germany, Mexico, Poland, Romania and Turkey.
What is a Thunderegg? Lore & Legend
The name “thunderegg” is believed to have originated from Native American folklore. Thundereggs were associated with thunderstorms or the rumbling sound of thunder which is said to be from angry “gods” throwing rocks at each other.
Some believe that thundereggs are grounding and soothing stones that have healing properties for the body, mind and spirit, especially in the area of addiction. Thundereggs are also thought to enhance one’s immune system and help resolve emotional problems.
This story about what is a thunderegg previously appeared in Rock & Gem magazine. Click here to subscribe! Story by Richard Gross and Pam Freeman.
