Thunder eggs vs Geodes

[PinkDiamond]

I never really gave this a thought before, until the Gem Society's newsletter had a link to this. What's your opinion? With or without a space inside?

Thunder eggs vs Geodes

http://rockhoundingkw.blogspot.com/2011 ... eodes.html

[rocks2dust]

That's a very pretty egg.

Thundereggs are technically called lithospathae and always form within perlite flows with the agate cores within rhyolite shells. When there is no agate center, we call them "mud bombs" (aka, spherulites). A hollow thunderegg can also be called a geode, but all geodes are not thundereggs. Geode is a broader term for a hollow rock or hollow agate that can form in vesicular or amygdaloidal basalts, limestone, andesite and hollows in other rocks. So its best to go by the shell (which also has important clues to narrow down the origin) rather than whether or not it is hollow.