User blog comment:AgentG231/What specifically is the metal that Altair used when he built the Armor of Altair?/@comment-4705174-20130503224852

Maybe he made the armor with the same material as the Piece Of Eden, maybe the Apple showed him a place where he can find this rare metal. Also Mario mentions in AC2 that the armor whas very light but very strong, just like the Pieces of Eden.