Adamantine has not gone up against the forces that Mjolnir has. Also, Hercules was recently denting Adamantine in his series so it's not as if it can't be damaged.
Fun fact: Hercules' mace was breaking when he and the others attacked Superman after he beat Thor in JLA/Avengers #2.
uru is like ore or stone, so it doesn't have the flexible qualities as metal would have anyway.
i kinda agree with rage about the lack of similar punishment for both substances, though thor did whack that cylinder with mjolnir and left some sort of mark on it. the hammer was seemingly undamaged though.
Which means what? A spray of water at low power will disperse across a metal wall...
At the right force it'll cut through steel.
Other metals to consider when applying the rules of stones vs metals
bronze gold platinum titanium you can also consider the power behin the force
a jackhammer slamming through a concrete slab
try it with just a "hammer" and you well bend or snap the head to your Stanley hammer
And just because a hammer bs mace in all their confrontations appear tied doesn't mean that they are... The right force or angle of attack could destroy either by aiming for weak points in the structures
__________________ Quotes from Hia8:
"I claimed that the science is sometimes faulty."
"You don't understand. This is fiction. That means none of this stuff really happened."
"There is no writer to purposely ignore a character's natural ability just because it suits the story."
"in some cases because the writer knows that Character A will dominate Character B easily and refuses to allow this to happen for the sake of the story."