Hone ID - Water. Stone., Natural Gemany

[atercz]

Can anyone identify this hone please? I have two specimen. Both purchased in Japan. I tested only smaller stone. Stones description:

• It's very consistent finisher producing mirror surface (approx. 8 to 12k). Sharpening with slurry (released by Atoma #400) did not affect much resulting surface.
• Stone is not fast nor with slurry. Sharpening is slow like CF.
• Stone is harder. Harder than coti, but not super hard as CF.
• Slurry is white milk, same as coti slurry. Sharpening on slurry is slow and results is much better than on coti slurry.
• Stone is not slate. It has not layers and chipping is very specific similar to obsidian. Feel during sharpening is like on coti but this is not coticule. Also it is not novaculite.
• Color is very light brown, darker stains on bigger stone are dirt, they disappear after lapping and then dry surface is almost monolithic. Wet surface contains darker stains. I saw similar stains on synt. King 6k S-3. Maybe this stone is reconsolidated natural stone.
• Bigger stone dimensions: 201x25x76 mm, weight 975g, Smaller stone: 183x77x19,5 mm, weight 712g

Photos of large stone:


Smaller stone: