thunder egg
noun Geology.
a globular concretion of opal, agate, or chalcedony weathered out of tuff or basalt.
Compare
geode.
Origin of thunder egg
First recorded in 1940–45
Words nearby thunder egg
thumping,
thun,
thunbergia,
thunder,
thunder bay,
thunder egg,
thunder mug,
thunder sheet,
thunderation,
thunderbird,
thunderbolt