Adventures in Thary
Being unable to tolerate the stinging bite of worked metal, they Fey instead grow crystals into the shapes of things they need. The crystal is as hard as steel but lighter, any item typically made of metal will weigh half as much in fey crystal.
In addition, as arcane magic is as part of the fey as blood to mortal creatures, the crystal helps with the flow of magic when it is grown into armor. Fey crystal armor reduces the chances of arcane spell failure chance by 20%.
Crafting of fey crystal items must happen in the fey wild and takes no longer then forging items as on the material plane.
This rare and unique metal was only ever found in the mountain range of the Zheechdra kingdom, now long lost. The deluge seems to have wiped out the ore it was created from or the instructions to how to smith it. As hard as Adamtnium but as light as Mithril, any weapon crafted using this metal is considered magic granting a natural +1 to attack and damage rolls. Any armor is also counted is magical, granting a +1 to AC.
Zheechdra metal is needed for crafting many of the items the civilization was made for, but can only be obtained by melting down preexisting items made of it.