In this question we came up with a weapon that would be quite powerful if it could have variable weight and inertia. In the comments of the accepted answer a user pointed out that we basically invented Mjolnir, Thor's hammer. And I agreed, it basically can do anything Mjolnir can except conjure lightning, you could even fly with it if you were
brave stupid enough to actually throw the hammer while it is attached to you.
So in a Melee weapon that you can control the inertia and weight of, what type of material should it be made out of so it resists the potential huge impacts with other objects so it breaks the thing it is impacting without breaking itself? I feel like most common metals e.g. Iron, steal, aluminium, etc would be too weak.
The main concern would be a Hammer that is solid all the way through, though bonus points if you can have something fragile inside like electronics.