Thunder egg displaying faulted exterior, rock shop, Tucson, Arizona

Thunder eggs are products of circulating hot fluids rich in silica...circulating in hot volcanic ash. What amazed me about this thunder egg was the fact that a fault offset was quite evident. The ellipsoid had a conspicuous offset, which can be seen in the exterior views of this rock. I was ecstatic. How often do you find a faulted thunder egg? ;I could imagine the beautiful agate that would be inside, and I could “see” a situation where the delicate laminations would be offset along the fault. I could imagine that the agate would be crushed along the fault. I worked out a price with the owner (he sold it to me on per-pound basis), and I had it sawed and polished. The interior of the thunder egg lacked all signs of faulting. I cannot figure out how to explain the combination of faulting on the outside, and no faulting on the inside. Perhaps the original egg was an empty egg with a chalcedony outer wall. Perhaps the hollow interior began filling with gel-like silica. While the stiff outer rind of the wall of the thunder egg was being faulted, the interior of the shell was still filling with a gel-like goo, which was impervious to faulting and displacement. Perhaps the gel-like silica simply slowly filled the chamber. I still have not focused on the curves and bends of the agate laminae, and whether any relate in twists and turns to the faulting evident on the outside. ;I like this rock a lot, but I wish I could work out its history. ;Hope someone listening out there can help me.

In ~2002 I went to a rock shop on Dodge Avenue in Tucson, Arizona.  After looking around a while inside, I learned that there were a lot of specimens lying around in the backyard.  There I spotted this thunder egg in its native uncut form.

Age & Formation