Coal

Coal is a Zone 2 material gathered primarily from the Rotten Island biome, a decayed and hazardous region found in the mid-altitude range of 400 to 900 meters. It appears as black, sooty mineral seams within rock formations and can also be found among the ruins and debris scattered across Rotten Island. Coal has no smelting value on its own, but it is indispensable as a component in one of the game's most important alloy recipes.

Coal's primary crafting role is as one of the two ingredients needed to produce Steel Ingot at the Furnace, combined with Iron Ingot. Steel Ingot is a late-game advanced material used in high-tier crafting projects, making Coal an essential resource for players pushing into the upper tiers of the crafting tree. Without a steady coal supply, steel production stalls entirely, which can bottleneck progress on advanced weapons, armor, and construction items.

The Rotten Island biome where Coal is found is dangerous and filled with environmental hazards, so players should prepare well before venturing there. Bring sufficient food, armor, and weapons, and mine coal in large batches to minimize the number of trips required. Because Coal is consumed in a 1:1 ratio with Iron Ingot for Steel Ingot production, players who want to craft steel in volume should stockpile both materials in equal quantities. Consider designating a dedicated storage chest near your Furnace specifically for Coal.