Northwest quarries
Formed about 60 million years ago, Thunderegg or Thunder egg, is a round nodule-like rock formation, filled with agate, jasper, opal, and/or quartz crystals. Thunderegg is also called agate-filled or jasper-filled nodules. Typically, the size is from two to six inches in diameter. Rarely eggs can be one to three feet long and weigh over a ton. Some specimens contain two or three eggs connected together. The oval shaped thundereggs have been formed in the rhyolite lava flows and tuffs within the gas or steam pockets that served as molds. The pocket cavity was filled with silica-rich fluids and later solidified and crystallized. Mineral impurities are collected along the bands creating concentric colorful rings.
Hollow thunder eggs are known as geodes but not all geodes are thunder eggs.
The exterior surface is white-gray to reddish-brown, looks rough and unattractive but the inner content may surprise you with its impressive crystal formation and colorful mineral patterns. To reveal the natural beauty of eggs, they should be cut in half and polished.
