Help identifying stone

[thisusernamealreadytaken]

Could somebody please tell me about this stone I got in a group of mostly Arkansas and India stones? I believe it says "Tashiro Co Made in Japan". I usually sharpen carbon steel knives and tools with Arkansas stones and diamond plates. Thanks for any info.

 

[cotedupy]

Looks like a small bit of Aoto to me.

(Though I'm not a huge jnat expert mind.)

 

[ethompson]

A chunk of rather hard mizu asagi seems like a possibility to me as well

 

[thisusernamealreadytaken]

Warning: stupid question ahead. What would this be used for?

 

[ethompson]

Most likely being used as a tomo nagura to raise slurry on a bench stone