If you buy them second hand they don't always. Boxed Thruingians and Eschers don't always have a space for a slurry stone.
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One tip off of a thuringer is that it will be deeply scratched/nicked and the honing surface is usually slicked/glossy. If you take a piece of 220 grit sandpaper with you and sand the side it should sand very easily and come off as a bluish powder.It will remind you of chalk. The size is usually less than 2" in width and from 4-7" in length by 3/4 thick.
Hope this helps,:)
Bluish chalky powder.... gotcha. After tink tink tinking a few different hones I think I may be able to tell the difference by sound as well, at least as far as Arkansas stones goes.
The harder stuff I have has a harder/denser ring to it, and the softer stuff has a chalky kinda sound.