Glowstone

Glowstone first appears in The Hero of Ages as a naturally occurring luminescent fungus that clings to porous rock columns, bathing the subterranean caverns of the Final Empire in an eerie blue light. Over the course of the Mistborn series, this bioluminescent growth evolves from a mere environmental curiosity into a vital resource for underground civilizations, its spores later harnessed for alchemical illumination and even rudimentary Allomantic experiments. By the later books, glowstone becomes a symbol of adaptation and survival, representing how life persists and innovates in the wake of cataclysmic change.