Phraxdust was a substance created when Stormphrax crystals were ground into dust during twilight. A fine sepia-coloured powder that seemed to flow like liquid, Phraxdust was both extremely explosive and capable of purifying the foulest of liquids. Because of these properties, it was one of the most prized substances in the Edgeworld.
Phraxdust was discovered by Vilnix Pompolnius during his experiments on Stormphrax crystals that he stole from the Treasury Chamber. He created the substance entirely by accident, and secretly had no idea how it was made. Each time he tried to recreate the original discovery, it ended in a violent explosion. Despite this, he was able to use his discovery to boost his status to Most High Academe of Sanctaphrax, and struck a deal with the League of Free Merchants. In return for Phraxdust, the Leagues created extra chains to anchor the Sanctaphrax rock in place, which was becoming dangerously buoyant because of a lack of Stormphrax. As more chains were manufactured, the chain factories pumped more pollutants into the Edgewater River, requiring more Phraxdust to purify the water, more stolen Stormphrax to make Phraxdust, and thus greater destabilisation of Sanctaphrax. This vicious cycle was ended when Twig brought back a chest full of Stormphrax collected by Screedius Tollinix. Twig also discovered why Vilnix had been unsuccessful in creating more Phraxdust: the conversion of Stormphrax to Phraxdust could only successfully take place when illuminated by twilight. The first time Vilnix had been lucky in that he began the process the exact moment twilight fell.
In the Third Age of Flight, phraxdust found numerous practical applications in the daily life of Edgeworld inhabitants. For example, its water purifying properties could be used in sinks, and its explosive properties could be used in Phraxships and firearms.