The weapon fired from an Eidelon fighter.
The Eidelon crystallization weapon was the device used to strike down Aeryn Sun and John Crichton while they sat in a boat on a seemingly uninhabited water-covered planet following the destruction of the wormhole that led to Earth. It was fired from a vehicle and transformed John and Aeryn into a mass a crystals which then fell into a pile. ("Bad Timing")
Fortunately, the process was reversible. Targets were "neutralized" for later analysis. After collecting all the pieces from the boat and the ocean floor, a Diagnosan was able to structure the crystals properly and a machine provided by the Eidelons restored Crichton and Aeryn to their pre-crystallized states. (Farscape: The Peacekeeper Wars: "Part 1")