Fossils are cubic natural blocks that can be found on the Fossil layer underground accessible through Caves, and sometimes even on the surface at recesses close to rivers.
Mining these blocks does not require any Power Cell to be equippped since R39 in February 2017 anymore.
Since February 2017 Bones can now be put in the Forge to be changed into blocks of Fossils. The balance is still a work in progress, as the developers claimed, but for now (June 2017), 1 Bone can be forged into 4 blocks of Fossils.
Obtaining Fossils is one of the unlocking requirements for the crafting recipe for Asphalt.
Fossil blocks are also an ingredient in crafting Gas Lamps.
One Fossil block can be processed into 1 Bone each in a Processor. No crafting recipe is required for this.
Occasionally, blocks of Fossils can be obtained from Warmworms, Dustevils, either when killing them or harvesting from them when they are Pets.