Fossil Eggs and Pits
Here I was playing with the same basic patterns seen applied in Alien Mandala. I find the texture reminiscent of some layered gemstones I've seen, though I'm not versed in lapidary and can't think of what they're called.
Later note: It seems agate is the name I was looking for. Though it takes many forms, agate is frequently found layered and may look similar to this when polished.