David Weaver
It's a barber hone.

Not easily usable for tools. Barber hones were usually coarser abrasive (like #1200F) with a surface treatment intended to tone them down so that they could be used to keep the bevels of a razor flat.

most of them advised against using the hone all the way to the edge (the linen and leather would manage the very edge of the razor, all you had to do with a stone was keep the geometry behind the edge in check so that the edge itself didn't get thick and blunt).

It seems like there are about a million different razor hones, yours is probably a pike. Franz Swaty is one that's popular now because people like to get these hones and then try to use them as a finish stone. The instructions that come with them usually say "when a razor first starts to pull, make four passes over this stone dry or with lather and then shave again.". they have a diagram showing the shape of the stroke to hone a razor and sometimes a comment along the lines of "avoid overhoning".

Overhoning is the subject of great debate, but in the context of those hones, it just means don't overhone all the way to the edge or you'll have deep scratches and a toothy shave.

the shaving forums are full of supposition and guessing without experience, combined with moderators who are involved in it and ban people who question them (I haven't been banned but I don't frequent them - they're like sawmill creek. "what stone should I buy". "My razor isn't sharp, can someone give me instructions to sharpen it?").

maybe more than you were looking for!!