Silvery, magical dust
Raw residuum is generated by planar conjunctions and the disenchantment of magical sources. It can be used to create magic items, fuel rituals, or enhance spells. However, raw residuum is known to be unstable – although exactly what this means, most people are unsure – and most cities (including Gis Galen) ban it, requiring that all raw residuum be immediately worked into half-forged residuum via the Enchant Magic Item ritual. Now and then a merchant will attempt to trade in residuum, but more often than not such people quickly end up mysteriously disappearing.