Not to be confused with the Black Crystal, which are mere fragments of its great evil powers.The Malefic Black Crystal, or Jakokusuishou (邪黒水晶), was a large black crystal from Sailor Moon R which grew stronger with more negative energy. It was a crystal from the planet Nemesis that Death Phantom used to try and destroy the Earth. The Black Moon Clan intends to let it grow enough to open the Black Gate and allow the world to be destroyed.The leaders of the Black Moon Clan, with the exception of Saphir, wore earrings made of this crystal.
In the English dub, this crystalline substance was called "the Dark Crystal," in the Tokyo Pop manga translations it was called "the Black Poison Crystal."
In the second season, the Malefic Black Crystal was in the very heart of planet Nemesis powered by a reactor that greatly strengthened its evil. Wiseman had a large orbicular fragment of it which he used against Sailor Moon (as Neo Queen Serenity) and Chibiusa's Silver Crystals. The Crystal also acted as a key to open the Dark Gate. Black Lady attempted to fully harness and channel its vast amounts of dark energy into herself to obliterate the Earth.
The Malefic Black Crystal plays a similar role it had in the original anime. Wiseman said that the Black Crystal rivaled even the supremely powerful abilities of the Silver Crystal itself and it possessed the power to dominate everything.
As a crystallized stone of pure evil, it has complete power over the element of Darkness (Shadow) and is capable of projecting supremely strong and destructive bursts of evil energy, leaving destruction and decay in its wake. It also has the ability render anything or anyone directly linked with the Silver Crystal itself utterly defenseless and powerless.