"Thunder Egg"

Item Description

A cool specimen of the famous Thunder Eggs in north-central Oregon. There is a bit of confusion and controversy as to how Thunder Eggs form, but they are very popular in certain collector communities. The specimens from near Madras have beautiful internal blue coloration of Agate / Chalcedony (or some other form of cryptocrystalline Quartz) with a firm outer Rhyolite "shell" or coating. A listing on mindat.org surrounding these nodules that "An origin for thunder eggs that has been proposed is that they are the interior of cavities/vesicles/gas bubbles in rhyolitic lava flows. As the silica-filled cavities are harder than the surrounding rock they are often weathered out, or partly weathered out, of their source rock". The interesting aspect of Thunder Eggs is that they found as rounded concretions and typically have similar internal and external features. This piece was sliced and polished, to better show the beautiful pattern and colors inside.