The Cyclone Gem is an essence gem which provides players with a shield which damages enemies who come close to them. It is usable by characters of any alignment, unlike the similar Gem of Storm's Rage (Closed Fist) or the Heaven's Blessing Gem (Open Palm). It can be purchased from Zin Bu from the start of Chapter 5.
In-game description: "Among the first monks who developed the Tempest style, there was one who began to question the Closed Fist tenets of his order. Ostracized from his ruthless order, the monk sought new ways to harness the wind without relying upon Closed-Fist chaos. By focusing his hatred for his old order into a handful of small stones, he managed to replicate the power of Tempest in those stones. A stone of this type surrounds the wearer in swirling winds that whip and tear at any who harm the stone's wielder."