FFO Name: Adamantite
"Legendary metal renowned for its strength."
The Adamant is found in the Sky Castle. Take it to the Dwarven Blacksmith so he can make you the Xcalber.
Adamant is Adamantite in the Japanese version. I assume that means adamant ore. Adamant is a mythical metal that's supposed to be extremely strong. It comes from the Latin word Adamas, which means "the strongest steel" or "durable". The Latin word Adamanteus means "as strong as steel". The modern English word Adamant (stubborn, unyielding) comes from this as well. Adamantium is a super-strong metal found in the Marvel Comics universe, most notably it lines the skeleton of Wolverine from X-Men. Adamantite can also be found in FF4, where you also take it to a blacksmith to make Excalibur. Adamantite can also be found blocking your path in a certain dungeon in FF3j. Finally, there is a monster called an Adamantaimai in most later FFs, sometimes translated as Adamantoise, or something like that. (A taimai is a Japanese hawksbill turtle.)