#723 Atago XXXL Type 24 Hard Sub Mirror 4.5 hardness 4.5+ fineness 3418grams

Dense, hard and very slightly self slurrying, not the easiest stone to use but also for a stone of it's hardness it is not overly strict. A massive homogenous 'potato stone' good for polishing razors and for fine finishing knives that work with this fine a finish. 

These might not agree with high alloy steels or large carbide alloys. With the use of a nagura, a stone of this hardness and fineness is useful on knives like yanagi or usuba that benefit from a very fine finish on the ura (inside hollow ground side).

This stone might be scratchy at first and will need to be flattened and the face polished with hard tomonagura or hard nagura. 

Atagoyama:

A central mine on Mt. Atago that produces homogeneous stones of various types like Suita and Tomae. Known for their polishing power and not being too hard, unless stated.

222x84x73mm 3418 grams