Titanium

Category:Resources
Strong, light-weight element used in mid-durability modules.
Used in: Practically all tier-II weapons, armor, propulsion, etc. modules
(spoilers!)
 
Common sources: Harvesting of resource drops from broken-up asteroids in select regions, bonuses from surveying Anomalies, purchases from Trade factions on the cheap (e.g. CXTA, Trade Guild, Aquarian Traders)
Remarks: If you build up a reserve of 1000-2000 Titanium, you should have enough to outfit the largest ship with medium-durability modules, or resell your excess to Wiskamug or the Ermyr Defenders.