Cobalt is a quest item in Fallout 4.
Gameplay
A sample of cobalt can be discovered within the Cambridge Polymer Labs, initially found as unidentified sample 49. Once the sample has been loaded into the polymer coating applicator, the option 'scan loaded reagents' needs to be selected from the applicator terminal in order to identify the sample by its chemical name.
While the cobalt sample can be placed into and removed from the applicator, it will remain a quest item even after the quest is completed, and otherwise cannot be removed from the inventory.
Location
The only sample of pure cobalt can be found within the Cambridge Polymer Labs, and is located in the office directly above the clean room, on a desk where Tom Franklin's skeleton is found.
Notes
Cobalt exists on the Periodic Table of Elements in the Children of Atom Shrine on the Island.
- Pure Cobalt flux is listed as an ingredient of Fusion Cores in Fallout 76.[1]