My random thingy is a Petoskey stone. It's the official state stone of Michigan. I found it -- unpolished and half-covered in concrete -- in a gravel parking lot outside Traverse City when I was ten-years old. It's size is one inch by two, but it was considerably larger before the tumbler polised it to near perfection. I won't bore you with the details of this cool fossilized coral, but here's the
link if you want Wikipedia to bore you with details.
That's the 'top.' Oh, ah!
In my opinion, the 'bottom' is not as impressive.