The Black Moon Stone is a discovery found in the Dark Rift.
This rare, Black Moon Stone holds tremendous power. It can turn positive energy to negative, and vice versa, but a practical application for this ability has not been found. There are rumors of a lost Black Moon, but the truth remains unknown.
To find it, go to the center of the rift. You will see several black moon stones glowing everywhere, but the one you want is in the middle of the room, where a large black glow is.