Phraxdust is made by grinding Stormphrax down, and has the incredible property of purifying water. A single grain of it turns the most toxic sludge into crystal clear water. InThe Edge Chronicles, The Professor of Light from Sanctaphrax dies after coming out of The Twilight Forest, where death is impossible. He falls into a sinking mud hole and his Phraxdust turns the mud into pure water.
It was discovered when a sanctaphrax academic named Vilnix Pompolnius stole some of the sacred Stormphrax from the treasury of Sanctaphrax. Stormphrax is made of solid lightning, and Vilnix wanted to see if he could tap into its power. He, and the others in the Faculty of Raintasters, tried hundreds of different tests and experiments to harness its power, until eventually Vilnix crushed it with a mortar and pestle in anger. He observed the amazing properties of the new Phraxdust, and decided to make some more, but when he tried to grind a second piece, the Stormphrax released its energy in an explosion that killed all of the assistants. Still pondering over the mystery, Vilnix used his new Phraxdust to make himself "Most High Academe" at the top of the Sanctaphrax hierarchy.
When Vilnix Pompolnius came to his seat of power, there was a problem in Sanctaphrax. The giant floating city was becoming too buoyant and if nothing were done it would snap the great anchor chain and float off into the sky. For centuries Stormphrax had weighed the city down, but because Vilnix stole some, the anchor chain was threatening to break. Vilnix had the factories of Undertown build great chains and weights to attach on to the Sanctaphrax rock. This polluted the Edgewater River, so Phraxdust was used to purify it. It was still unknown how the Phraxdust was made in the first place, and every time Vilnix took more Stormphrax for his experiments, the city got lighter. Another problem was that Vilnix only sold his Phraxdust to the already-powerful Leagues of Undertown, so they controled all clean drinking water.