new/old hone ID

I found this old hone today in a junk shop today, paid 2 pounds so big deal if its no good. It had what looked like a crack in the middle and when I took it out the box it was in two bits, cleaned most of the old oil off it tried to lap it but it is real hard, use a small coarse dmt to see the slurry colour and it is white
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Any help appricated, it was also very dished but the back side is quite flat

Bit more info took this stone to a belt sander with a 80 grit belt to try and flatten the surface and slow proggress man this thing is hard, but got the colour a bit more regular brown with yeloow bits this is all the way through the 80 grit did not even leave any scratches still real smooth, someone must have really liked this stone as bevel was more than 5mm so a hell of a lot on a stone this hard

Washita soaked with oil. Originaly it would be yellow with small brown spots. If you are lucky it could be a good bevel setter.