Beautiful Polished Thunder Egg Half Geode Nodule Specimen Great Star Pattern Quartz Pocket

Collector notes

A thunderegg is a nodule-like rock formed in volcanic ash that looks like an ordinary stone on the outside but reveals intricate, colorful patterns of agate, chalcedony, or quartz crystals when sliced in half. Often roughly the size of a baseball, they are the official state rock of Oregon. Millions of years ago, silica-rich lava (rhyolite) and volcanic ash cooled. As gas pockets or voids formed in the cooling ash, mineral-rich water seeped through the porous material. Over eons, dissolved quartz and silica deposited inside these voids in alternating layers, creating the banding, colorful orbs, and sometimes star-shaped cavities that characterize a thunderegg.