Mined from certain rocks, usually found high on mountains, in caves, rivers, or deep water sources. Can be refined in a forge or used on machines like the Fabricator.
— In-game Description

Metal is a natural resource gathered mostly from golden, metal rocks that are abundant in mountains and caves, and rarely from normal rocks. It can be mined via a pick, hatchet, or creature. The most effective way being the Metal Pick or Ankylosaurus.

Metal is scarce in the beginning, and becomes more essential as one progresses. The golden, metal rocks were added to the mountains in patch 174.0.