Amakusa

Very coarse Natural stone that works best with Cladded knives but can also be used on mono steel as it get bur very quickly 
aprox. 400-600 grit 
Coarse natural Stones scratch patterns is much easier to take out with finer stones then synthetics or diamond 
That is a main advantage of having very coarse natural stone 
It can be used on all Sides 

Size. 215mm 70mm 60mm

Image is just a sample