Fossil Block化石のブロック

Layers upon layers of living matter have been crushed into a dense, twisted mass.
In-game description

How to get Fossil Block

Can be dug out of the ground or walls (The Passage)

Scene containers, dungeon placements, guaranteed drops and natural spawns are based on the Obtaining data of the Core Keeper Wiki (Fandom) (CC BY-SA 3.0), because these are not in the game files this site reads. Scene names are the wiki's English names.