-Oxford Dictionary of Earth Sciences pp 238-9

Some call any round rock a geode, while others insist it must be hollow, which I find weird because the filling of cavities is a process that normally continues to completion. So just before that last tad of void is filled it is still a geode, then suddenly it no longer is?


- Webster's Ninth New Collegiate Dictionary p 513

Three separate occurrences have been confabulated. 1. Amygdules, 2. Lithophysae, and 3. Mineral filled voids in sedimentary strata. Part of the confusion is because the three separate kinds of voids are all basically filled the same way. Ground fluids enter the voids and depending upon the temperature and content leave deposits on all surfaces or the floors if gravity is able to overcome temperature induced kinetic energy.





1. Amygdules form in what were originally gas filled bubbles in basalt.

2. Lithophysae are developed from spheroids or spherules that grew in molten rhyolite or obsidian.
I prefer the term "Thunderegg" from the tribes of the U.S Northwest.
They saw a war between two mountains hurling Thundereggs at each other.
Thundereggs

3. Sedimentary voids are what they are. I believe they should be called nodules rather than geodes.
Usually body oils bind clay to protect fossils. Here somehow apparently silica was attracted instead.
http://www.mindat.org/mesg-17-253403.html MIDWEST USA SEDIMENTARY TYPE GEODES

Not surprising that even the "experts" are confused. "Geodes" are usually tougher than their surrounding materials and may survive multiple weathering processes to appear in divergent strata vastly different than their original home, sometimes all three types found in the same sedimentary strata.

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