Geode
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A geode is a geological secondary formation within sedimentary and volcanic rocks. Geodes are hollow, vaguely spherical rocks, in which masses of mineral matter are secluded.
Quartz-filled geode, shown from inside (top) and outside (bottom)
Reddish chalcedony geodes
Very large amethyst and regular quartz geodes
Thunderegg
Videos
A thunderegg is a nodule-like rock, similar to a filled geode, that is formed within rhyolitic volcanic ash layers. Thundereggs are rough spheres, most about the size of a baseball—though they can ran
Geode
…potato stones". The term geode generally describes hollow formations. If the rock is completely solid inside, this would be classified as a nodule or thunderegg. 'Crystal cave' is both an informal term for any large crystal-lined geode and also used for specific geoheritage locations such as the Crystal Cave…
A thunderegg from the Black Rock Desert in Nevada that has been cut in half
A thunderegg from Succor Creek on display at the Oregon State Capitol
A thunderegg agate from Falen Tree, Oregon, US
A jasper thunderegg from White Fir Springs, Oregon