A few years ago I found this unusual looking rock while walking around the beach of Cape Code, MA, USA. My guess is that it is sandstone, but I didn't see any others like it on my stay. It is has smoothed out edges, and is about 2 inches in height.
Update: Lightness - It seems lighter than rocks of similar size
Hardness: 3 - A dime scratched it a bit, but not my fingernail