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I'd try giving it a brisk rubbing with a heavy carbon steel knife (no stainless) then wash it off with cool clean water to flush it.next give a coat of oil and see what the scratch pattern looks like.

In the first pic you can see the little grooves in its surface.these tell you it likely is a soft and lacks a good high specific gravity number that denotes a fine edge imparting characteristic .

195440 this stone is a true surgical black and is a very fine finisher.

195438 it sounds as though you either got a soft black Arkansas stone in B grade which is a very course soft ark suitable only for course grinding or a soft ark like the one in this picture that...