When discovered, a Fossil comes in the form of a covered Fossil, and can be put into a Fossil cleaner to be identified as one of nine different Fossils. These cleaned Fossils can then be placed into a Fossil machine to be revived into Pokémon. When placed, a Fossil cleaner takes up one block of space. It can be retrieved by mining it with a pickaxe.
A Fossil cleaner does not have to be placed next to a Fossil machine in order for it to clean Fossils. However, a Fossil machine is still needed to extract the DNA of ancient Pokémon from the cleaned Fossils.