What have I got here?

[Soconmtneer]

My mom gave me this with some of my Granddads old stuff.
She told me she used to watch my Great Granddad sharpen his pocket knife with
it when she was a kid. I don't know much about shapening stones. Looks like some sort
of black guey stuff is rubbed on it. Is it some sort of very old sharpening stone?
What kind of stone is it?

 

[jimnolimit]

that looks like a natural stone and the black stuff is the particles of steel taken off the edge during sharpening. i would have to hold and inspect the stone to see if i can identify it. from the pic you posted above, that might have just been a stone he found and not an actual quarried stone.