Never Again mine

Never Again thundereggs were mined by Paul – the Geode Kid –┬áColburn. Paul Colburn was looking for and cutting thundereggs a life long. He used his experiences to write a book about the forming of thundereggs. It is recommended to every thunderegg-lover. It contains ao a model on thundereggformation based on cristobalite crystalization.

The Formation of Thundereggs (Lithophysae), Robert Paul Colburn.
http://www.zianet.com/geodekid/