thunder egg

noun

Geology.

1. a globular concretion of opal, agate, or chalcedony weathered out of tuff or basalt.

Word History and Origins

Origin of thunder egg¹

First recorded in 1940–45

Example Sentences

Steve Manford, who works at clothes shop Thunder Egg, said the arcade had had "a renaissance" in recent times.

Read more on BBC

“It was like a thunder egg,” he says.

Read more on Seattle Times