Deepiron
Adamantine is one of the hardest substances in existence. In the eyes of architects, engineers, and warlords across the land, nothing can take its place as the most resilient of all building materials. Many a warrior owes their life to the plates of adamantine across their chest.
Description: Possessing a dark, non-reflective surface and surprising density, adamantine can weather blows that would crush any lesser metal. In contests of force, adamantine surpasses almost every other substance and emerges unblemished.
Natural Properties: Items made of adamantine are much harder to break. Increase the AC of the item or the DC required to break it by 5. (This does not increase the AC of a creature wearing adamantine armour).
Weapons: May reroll damage on Fey and Celestials, keep new result.
Armour: Advantage on saves from Fey and Celestials. +shield AC to saves from Fey and Celestials.
Example Item: Adamantine Lock: Adamantine's stalwart resistance to harm makes it ideally suited for protective measures such as locks.