Aluminum - GuillermoNigote/Radiant GitHub Wiki

Aluminum is a metal with Investiture-inert properties. It is only naturally produced in volcanoes, and therefore cannot be found in the Overworld. To obtain it, you must travel to the Nether, specifically to the Basalt Deltas biome, where its ore can be found embedded within basalt blocks. When mined with a stone pickaxe or higher, it will drop aluminum nuggets, which can be crafted into ingots like any other metal.

Thanks to its Investiture-inert properties, aluminum cannot be affected by the Surges or weapons of the Knights Radiant:

Aluminum blocks cannot be influenced by the Surges of Division, Transformation, or Adhesion If an entity is wearing an aluminum chestplate it will not die instantly when struck by a Shardblade If an entity has an aluminum shield or sword in their off or main hand it will also not die instantly when struck by a Shardblade without the need of blocking