Iceburst Stone

Iceburst stone exists only on Paradis Island, concentrated in the caverns beneath the factory city. Those caverns were once volcanic calderas; as the volcanism died and underground temperatures fell, the trapped natural gases compressed and froze into solid, ice-like stones. Warm one above the frigid temperature of its cavern and it vaporizes almost instantly, producing the small explosive burst that gives the mineral its name.

Zeke Yeager offers a stranger origin. He tells Kiyomi Azumabito of old whispers that the King of the Titans carved enormous holes on Paradis and filled them with treasures forged through the power of the Titans, stones that burn and stones that glow. By his account the mineral is impossibly rare, and the islanders have no idea what their resource would be worth abroad; in his words, it could turn a struggling nation like Hizuru prosperous.

The stone's value lies in packing huge volumes of gas into a compact solid. Chunks are loaded into canisters fashioned from iron bamboo, and applying heat releases the pressurized gas that drives vertical maneuvering equipment. The process is unforgiving: handled or heated incorrectly, the gas can kill its user.

Hizuru later pushes the mineral far beyond maneuvering gear, adopting it as the fuel that powers the flying boat, the aircraft that ultimately carries the alliance to the final battle.

The military forces of Eldia depend on iceburst stone for every launch of their maneuvering gear, making it the quiet foundation of humanity's entire anti-Titan combat doctrine. Hizuru becomes the second great beneficiary after Zeke's gift of a sample convinces the Azumabito family to back an Eldian alliance, leading directly to the flying boat's development.

Its real-world echo is methane clathrate, the frozen methane ice whose formation and explosive vaporization the fictional mineral closely mirrors.