In Reply to: What the????? posted by Elmore on Sunday, 9. March 2008 at 16:29 Bali Time:
A thunderegg (or thunder egg) is a geological structure, similar to a geode, that is formed within a rhyolitic lava flow. Thundereggs are not actually rocks, but rather geologic nodules which occur within other igneous rocks.
As there are volcanoes in Indonesia there is a possibility of obtaining a Thunder egg in Bali.
Pedas