I am new here and I have what I think is a straight razor hone. It is 5" x 2" x 3/8" ,very dark brown, smooth, hard like a piece of ceramic, and marked NEDRO. It belonged to my great grandfather who died in the 1950's. It was given to me along with his straight razor and pocket knife.
I have used a knife on it like a strop, but I can't tell or feel if it is honing any at all.
Google searches haven't turned up anything. Any help would be appreciated.

TIA, Dennis