Medonas "Snowball" Agates

Like the Las Choyas "Coconut" agates, these Snowballs from the Medonas Dune Field, Chihuahua State are sometimes considered to be a type of fully expanded thunderegg. The ones I've seen in the flesh really don't offer much or any sign - but I have seen photos of specimens with traces of rhyolite shells. See the Dwarves Earth Treasures, for instance. Whether this means that all Snowballs are secret thundereggs, or a few lithophysae have been found there among them, or something else entirely, I'm really not sure, but it's enough for me to include some examples here.