The Gem of Storm's Rage is an essence gem which provides players with a shield which damages enemies who come close to them. It is only usable by Closed Fist characters, but other characters can obtain much the same effect from the Cyclone Gem (no alignment requirement) or the Heaven's Blessing Gem (Open Palm). It is obtained at the Lotus Assassin Fortress from third piece of the Dragon Amulet after defeating Grand Inquisitor Jia.
In-game description: "This gem wraps you in whirling winds that tear at any who attack you. Its effect is constant while the gem is equipped."