Many thundereggs have recorded geologic events, as has this one from the "Potato Patch."
We now know a lot about them, such as:
They form in rhyolites, obsidians, perlites, and hot ash flow tuffs (Thanks Nate!). We can calculate when the flows occurred.
They begin as spherulites. Expanding gas presses them open. Ground fluids slowly fill the voids from the outside to the center and/or bottom to top.

What we don't know is where they start crystallizing. Inside the volcano? As they flow? After coming to rest?
There seems to be evidence for all three.

This pair is fairly straight forward to read. After the conjoined cavity was forced open a small amount of fluid entered and coated the entire chamber with white opal/agate. Later more fluid entered and settled into the bottom corner as small layers of opal, then a red layer of agate, another small amount of opal. In both halves the blue agate that later filled most of the cavity is clear enough to see the flat layer covering the floor of that deposit.

Note that later fractures have allowed moisture to enter and transform some layers of blue agate to opal for short distances. The top of the blue agate became a layer of white opal. Two more sequences of agate/opal followed with a red top finish. The left half shows a stalactite (remember a person with ants in their pants. When the mites go up, the tights go down) that was clearly there before the last fill sequences.
The host rock shifted slightly (tilt) before the final agate/opal fill solidified. The thunderegg cap on the right half broke off (just above) allowing a clear view of the top of the layer.

So what was going on geologically in the Blue Bed area to generate these fill episodes?

This example from the Baker Egg Mine reveals the host rock was shifted at least four times during the early fill sequences. Perhaps it was on a side hill and slowly tipping down? Note that the first thing to happen in the cavity was a dark layer of fortification agate that filled the chamber. Then came the layers of dark agate, a few layers of lighter material. The composition of the fill material is constantly changing. Why?

This example is a little harder. Which came first, the flat layers or the surrounding fortification agate? Either the outer layers came first, then the center layers filled in; or the flat layers filled the area, then somehow the outer areas "reorganized."
I can talk myself into either answer. What do you think?



Obviously there was a lot of minerals in the area when the Priday Plume thundereggs were filled. Notice how there seemed to be pressure pushing the top part to the right?
Multiples always catch my eye anymore, especially if the pairs have filled differently from each other. Were they formed in different parts of the flow and somehow got moved next to each other before solidification? Did collisions jar the jell?
Your comments, observations and suggestions would be appreciated!