Slime fossils are an uncommon resource obtained with a drill.
Prized for the ancient minerals they contain, slime fossils are like nature capturing a moment in time. Specifically, that moment seems to be when a great avalanche or mudslide occured and a slime was totally cool with it.
On the Ranch:
Deposit slime fossils into the Lab's refinery where it can be used for crafting Slime Science gadgets.
Treasure Pods that contain Slime Fossils
Crates that contain Slime Fossils
Only crates dropped by Gordo Slimes caught on a Gordo Snare, or from those dropped by the Crystal, Hunter, Dervish, Tangle and Mosaic Gordos found in the wild, can contain Slime Fossils. The chance you get a Slime Fossil from these crates is the same as its rarity.
Recipes that use Slime Fossils