+1 what Matin said. Not a Norton 4k/8k. But it does look like a very good stone which may be natural instead of man made! Can you give more info? How did you acquire it and when? What does it feel like when you run your finger tips across it (smooth, coarse)? Have you ever used it and if so for what purpose? What were the results of your use? Is the hone hard like stone or softer like a man made material?

Randy