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Geological Structures Known as Thundereggs

geological structure known as a thunderegg

What is a Thunderegg?

A thunderegg is a sphere-like geological structure that forms in lava flows.

The centre eventually splits to form a cavity which over time, fills with either chalcedony, agate, opal, jasper or quartz.

When the ordinary looking outer rock is broken open it reveals minerals within a self-contained centre.

Article Picture

Our thunderegg picture is courtesy of Captain Tenneal.  The photo is clickable and redirects to the original image.

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