thunder eggs

A specific type of geode (NOT synonymous with geode!) containing chalcedony.

Thunder Eggs
Three round geodes in small, medium, and large. The smallest one is a flat slab with a blue inside and brown outside. The medium one is a hemisphere that's black on the inside and gray on the outside. The largest one is a hemisphere that is purple amethyst crystals on the inside and brown on the outside.

Photo by Stephanie Reed

Some thunder eggs from the personal collection of David Reed. The largest one has purple amethyst crystals on the inside. It was originally from the collection of the late David White, who lovingly polished it by hand to a reflective shine. The medium one is from Oregon. The smallest one is a slab cut from a thunder egg and was from the Show-Me Rockhounds gift exchange.

Thunder Eggs

The thunder egg was declared the official state rock of Oregon in 1965, because there are quite a lot of them there. A thunder egg is a rounded nodule or geode with agate in the center.  Thunder eggs can also contain quartz, chalcedony, crystals, or opal.  The inside parts can be opaque or transparent – there are almost as many possible designs as there are agates.  This unusual thunder egg shown above is from Oregon and has plume inclusions. Some thunder eggs are also geodes but this one is not a geode because it does not have crystal points. A more typical thunder egg would look similar, but with bands or a single color on the inner part.