Mined from rocks or picked up loosely around the island. Can be farmed with an Ankylosaurus. Used as ammo in the Slingshot.
— In-game Description

Stone is a natural resource that can be gathered by picking up small stones, using apick, hatchet, or a creature. The most effective gathering method is via Metal Hatchet, Doedicurus, Dunkleosteus,or Ankylosaurus.

Stone can be used in a variety of applications: construction, ammunition for the Slingshot, and weapon and tool creation.