Residuum

Residuum is the residue of arcane energy, manifesting as a green dust obtained from whitestone that is useful in several magical applications.

Properties
Although not inherently magical, it is particularly receptive to arcane energies and therefore may be used to create objects that retain more powerful enchantments, perhaps for longer periods of time. It can also be utilized to replace and act as other expensive materials and components for spells and other uses. Finally, it is one of two substances that can be refined into the drug suude, which can enhance spellcasting.

Raw residuum can be purified by heating into a dark green glass-like state; in this form it is referred to refined residuum and displays stronger magical properties.

When Caduceus placed shards of refined residuum in the forge of the Cinderrest Sanctum, the crystals developed root-like tendrils and their color shifted to purple. They further transformed when dropped into The Menagerie's pool, developing long, thin, crooked, pseudopod-like extensions like a partially germinated seed.. Caduceus then gave them to Calliope to return to the Blooming Grove, per his vision from the Wildmother at the Arbor Exemplar, and she later reported she had planted them and they were taking root. Whether these transformations happen generically to residuum glass or were specific to the quest to heal the Blooming Grove is unknown.