Adamantine

Adamantine is an ultrahard metal found in meteorites and extraordinary mineral veins.
Melee weapons and ammunition made of or coated with adamantine are unusually effective when used to break objects. Whenever an adamantine weapon or piece of ammunition hits an object, the hit is a critical hit.
The adamantine version of a melee weapon or of ten pieces of ammunition costs 500 gp more than the normal version, whether the weapon or ammunition is made of the metal or coated with it.
Adamantine can also be used to create armor. While wearing metal armor made from adamantine, any critical hit against you becomes a normal hit.