Posted by Señor Albonio

It's because it's a reference to a quest that used to be in Graal years ago.

Wish I had known that.. Now I'm starting to think it was just in fact a randomly added loot item with no special purpose.  

Moon rock is a reference from old graal... they just like putting stuff like that in game...hopefully it will have q bigger reason for being there but for now I think its just for nostalgia