Adamantium is actualy extreamly brittle and easy to melt when raw, but once it cools after being melted it becomes indestructable.
Adn for those mentioning Vibranium, it is capable of nulifying physical force and is almost indesructable, but is rather vulnerable to energy weapons, as its power coems from negating force applied to it. As such, if an adimantium and vibranium weapon hit each other, niether coudl ever damage the other, but a Cyclops optic-blast could destroy the Vibranium, but not the Adamantium.