Glowstone

In the Mistborn series, Glowstone first emerges in 'The Hero of Ages' as a vital natural light source in the cavernous refuge of the Terris people, consisting of large porous rock columns at the base of which bluish luminous fungus grows to provide dim but essential illumination. This humble environmental feature underscores the harsh underground survival conditions amid the world's apocalyptic ashfalls and mists. Though not evolving dramatically across subsequent books, Glowstone symbolizes the adaptive resilience of natural phenomena in a dying world, offering faint hope in the encroaching darkness.