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This rock was found in Tywyn Wales looks like a worm eaten potato but is hard and smooth with eaten holes in it
Interesting find, how far do the holes go into your specimen?.
The cause of the holes could be an animal that bores into rocks or something like a softer mineral that has worn away.
I think Mike will be able to give you a better answer than me as to the type of mineral the rock is.
Actually v. difficult even to guess the rock type from the photo (they're both the same).
Certainly flints can have these sorts of holes, but there's a granularity to the surface that isn't quite right for flint (even allowing for a weathered rind).
I think, from the distribution of the holes and their similar sizes, it is more likely they arose from recent animal/plant solution/boring (some plants' holdfasts can dissolve depressions into rocks).