Kitebuilder.com

[Stan]

Yes it's a natural fine gray stone for oil. Probably what your father used to put the final edge on a blade. They are called Arkansas, Washita, and (really!) Queer Creek stones. It's probably easier to just buy a semiconical slip, but yard sales usually have stones for cheap since sharpening is a lost art, and they can be ground to shape.
I prefer soft Japanese ceramic waterstones and slips on my edge tools, but they aren't everyone's cup of tea.