The weapon took the form of a probe which could be fired at a planet. Upon entering the atmosphere, it broke into three separate probes that buried themselves into the planet's surface 600 motras apart. The probes cause harsh magentic shifts, destroying most of the complex life on a planet and rendering even Class M planets largely uninhabitable. The weapon was not well understood and had only been used successfully once -- on Arnessk.
On Arnessk, for reasons remaining unclear but likely due to the potent psionic abilities of the Eidelons, the triangle had actually frozen the entire Eidelon civilization in temporal-magnetic stasis. This stasis was reversed when the crew of Moya recombined the three probes.
The Darnaz Triangle was featured in episodes of Farscape.