Fossil ore is a type of block that generates naturally in the Overworld. It is generated in layers of stone and has varying looks to it depending on the type. In order to obtain fossils, you must use Plaster and Bandages on it, and then it can be mined by an Iron Pickaxe or higher.
Fossils currently come in these types: Cretaceous, Jurassic, Triassic, and Devonian, and their respective Encased versions.
Plaster and Bandage[]
Plaster and Bandage are a critical component to making dinosaurs. The recipe is one block of white wool (Must be white) surrounded by 4 pieces of paper (Top Right Corner, Top left Corner, Bottom Right Corner, and Bottom Left Corner) and 4 pieces of Gypsum Powder (Top, Bottom, Left, and Right). To use, simply right-click on a fossil ore, and it will become an Encased Fossil. Then it can be mined safely with a pickaxe without shattering the fossil.