Spirit dust is a product of defeated Elemental Spirits. Because the energy left behind of defeated spirits are physical particles, dragons have taken to harvesting these spirits to manipulate magic in ways that weren't possible.

Spirit dust is often used to embue certain items with magical abilities. In most cases, this is one by mixing in the dust at some point in the item's creation process (such as mixing the dust into ink, or into molten metal to make enchanted tools).