Strategic Resources
Strategic Resources (development) in the Stellaris encyclopedia: Strategic Resources are rare and potent substances critical to advanced technologies, infrastructure, and starship systems.
Strategic Resources in the game's words
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Strategic Resources are rare and potent substances critical to advanced technologies, infrastructure, and starship systems.
Examples include 
Volatile Motes, 
Exotic Gases, and 
Rare Crystals.
Rare Resources are even more valuable or and esoteric substances with particularly advanced applications. Among other things, Rare and Strategic Resources are used to construct Utility Ships, Military Ships, Starbases, and Megastructures.
To increase:
- Build 
Mixed Industry or Heavy Industry
- Construct associated Buildings
- Buy on the 
Market
More in Development
Source: common/game_concepts (concept_strategic_resources) and localisation/english, Stellaris Cygnus v4.5.2 (9776).