150 They are magic items with all their attendant properties. Its description is “A fighter can wear mithral chain shirt or breastplate under normal clothes.” Adamantine 5e and Mithral armors appear under the “Magic Items” heading of the DMG and are present in magic item tables. Mithral Armor is classified as Uncommon, so the DMG values it at 101-500gp. It applies to every condition, whether the weapon or ammunition is made of metal or coated with it.
XGtE says, ” In 5e dnd, The adamantine version of a melee weapon or ten pieces of ammunition costs 500 gp more than the normal version.
