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Dwarves' Earth Treasures Museum:
Bruneau Jasper Thundereggs
Bruneau Canyon, Idaho
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    Bruneau Jasper Thundereggs are one of several most popular type of jaspers and they're widely used in lapiary arts. They're best known for their "orbs/eggs" features that are sometimes revealed when cutting the jasper-filled thundereggs. It is my experience with the jaspers of Little Florida Mountains in Deming that the best jaspers seem to be found in the thundereggs embedded in the hard rhyolite beds. There had been reports of difficult mining to extract the jaspers out of the rhyolite lava beds (often misidentified as "welded ash beds") and the claims are still maintained even today in spite of the word about the area being turned into a national wilderness.
    It started with the mud filling in the cavities within the thundereggs and water would start to act on the mud, coloring it or producing the "orbs/eggs" within them. It is not certain whether the mud had been silicified before or after the colors and features are formed, but I suspect the latter. The colors are typically brown to orange with some yellow features, and some specimens come with red, and green. Some jaspers did suffer some cracking as a result of drying before the cracks were filled and welded by silica solutions, giving them "morrsonite" look. The sizes are generally small and I have personally seen one the size of basketball witth "orbs-eggs" showing on a chipped area at Quartzite, Arizona.

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Faint "mud" zoning.
Those without  any features are typical.		 This shows the fact that they are thundergg-types
which occur only in lava flows, NOT ash beds.

Classic "Orbs/Eggs" feature wtih brighter colord edges. SLAB