Orichalcum (オリハルコン Oriharukon) is a metal present in Final Fantasy XII, Final Fantasy Tactics, Final Fantasy Tactics Advance, Final Fantasy Tactics A2: Grimoire of the Rift and Final Fantasy Tactics S.
Orichalcum is both a legendary metal and a rare alloy with the strange property of becoming solid only at certain times of day, which lead to smiths nicknaming it "the phantom metal". Orichalcum seems to waver and shine like a flame, but burns cold, and is always used in statues of protection, such as the constructs of Pharos at Ridorana (which was built by the occuria), meaning it has been in use since the Age of Gods. Orichalcum is used in the making of Orichalcum Dirk, and is treated by smiths with the utmost care, known for being exceedingly hard and light at the same time.
Due to its strange state, some believe that orichalcum is not a real substance, and that it's the mere idea of the metal that lends protection, but its energetic reaction to incandescent flames seems to disprove the claim.