Invincibilium
A lightweight material renowned for being completely indestructible. Because it is completely unbreakable, mined Invincibilium cannot be processed into other shapes, meaning that any objects made from Invincibilium must have initially formed in that exact arrangement of atoms. Because of this, objects made of Invincibilium are incredibly prohibitively expensive.
A: You can't break that!
B: Just watch me!
A: No, you literally can't, it's made of Invincibilium.
B: Oh...
B: Just watch me!
A: No, you literally can't, it's made of Invincibilium.
B: Oh...