... This area is currently being worked by another friend of mine and has never been a big producer of thundereggs. I have never been to this location and have only seen a few specimens from here. These are very rare and desirable eggs if you can find them. I have only seen them available on E-bay a few times. The specimens are usually hen’s egg size with a greenish-grey matrix. The cores are almost always agate of a light blue color, can contain moss and sometimes will be fluorescent...”

extract of the article from Mark Ketsdever, Hillsboro, Oregon, 2007 :”Thunderegg Agates of the Ochoco Mountains, Oregon, USA”