Someone sent me these photos and this is on the eastern plains. I asked if I can see if in person to figure out other things about it. But maybe it is a dead give away on what it is based on what it looks like.
I haven't seen a small nubbin of rock with this kind of pattern.
Such banding, representing variations in mineralogy and hence potentially hardness, may come to stand out as a result of weathering. ...Or not, eg. http://paleo.cc/paluxy/nevada.htm
Because the surfaces in yours are at least partly closed, I can rule out the former.
A third possibility is that the iron-rich layers represent a fossil, the original mineral having been replaced with an iron-rich one. But what sort of fossil? None comes to mind that is a good fit. And I can't see any organic details.
I don't get much insight from the location, but thanks anyway.
So I think it is probably a concretionary banded ironstone, but there are some aspects that leave me unconvinced. That's the best I can do from the photos.
Somebody else here might have an idea. So stay tuned a while.