@mikemearls @JeremyECrawford Adamantine Armor says “any critical hit against you becomes a normal hit.”, but why does it effect spell crits? Book says it’s reinforced armor from the hardest substance on earth. Why would a super hard ore prevent, dmg from a psychic spell crit?
— Kantrism (@Kantrism) November 8, 2017
Adamantine armor is a magic item. It’s not a chunk of ore. #DnD https://t.co/qUdnQrmpi7
— Jeremy Crawford (@JeremyECrawford) November 8, 2017
Proper answer – it’s a badly named and conceptualized item, which leads to a lot of confusion, and which really should just be changed already with errata.
The fact that it is both made out of, and named after, adamantine quite naturally leads people to assume that its special powers should come from, and reflect, the special powers of adamantine itself.
But it doesn’t. It has an entirely separate power that has nothing to do with the adamantine construction, and which instead comes from the magical enchantments on it.
It really ought to…
1) Not make any mention of including any Adamantine in the construction…
2) Have a totally different name like “Merciful Armor” or “Armor of Glancing Blows” which establishes the source of its power as a magic effect…
…or…
3) Do both.
The inclusion of noting “adamantine” or “mithral” in the naming of “x” magic items is to indicate that while the material used in constructing “x” isn’t itself magical, the material itself is part of what allows the final enchantment to have “x” qualities, similar to how certain materials are required to cast certain spells or in the making of other magical items. (That is, it’s because the enchantment is used with armor made of adamantine that the resulting magic (game mechanic effects) exist the way they do, vs say conventional steel plate mail armor which might have “x” qualities (+X bonus, what have you) but doesn’t possess the qualities that the adamantine version does.)