"A geofact (a portmanteau of "geology" and "artifact") is a naturally formed stone formation that is difficult to distinguish from a man-made artifact."
Maybe that is a drilled hole in it or is it a natural hole? The outside doesn't looked like it was pecked and smoothed by humans.
Us redneck rock hunters call stuff like that 'foolers'.
Don't know what word I'm looking for here so I'll just say "pivot point" for a small mill stone maybe? The crack makes me think it was bearing some weight and the radial scoring looks like something may have been spinning around it.
"If you were supposed to watch your mouth all the time, I doubt your eyes would be above it." - DBT
"I am good at what I do, and I take great pride. But I don't make much money, so I sell eggs and chickens on the side." - WSP