Quartz

specimen number:
2072034

location:
Richardson Ranch, Madras, Oregon, USA

description:
A cut and polished half of what is known as a thunderegg, basically quartz.

Thunderegg agates are rounded, nodule like formations found in rhyolitic volcanic rocks, especially in regions such as Oregon in the United States. Despite their external resemblance to geodes, thundereggs are typically solid rather than hollow and contain internal structures of agate, chalcedony, or opal. They form when gas bubbles or cavities in volcanic ash and lava become filled with silica rich fluids that later solidify. Over time, these fluids deposit layers of microcrystalline quartz in complex patterns, often creating star like, mossy, or banded designs inside the nodule. The outer shell is usually composed of the host rhyolite, while the interior displays the more colorful agate or chalcedony. The name thunderegg comes from Native American legends that described them as stones thrown during thunderstorms, reflecting their distinctive appearance and occurrence in volcanic terrains.

Questions about this specimen?
Send an email or call us: 314-341-1811.