Iridium

Category:Resources
Hard, dense, silver-white metal.
Used in: Armor modules, Fighter Bay
(spoilers!)
 
Common sources: Bonuses from surveying Anomalies, destroying enemy ships, salvage from Imperial technology derelicts (Talonians, etc.), purchases from Trade factions on the cheap (e.g. selling the more-rare resources to the Trade Guild).
Remarks: Depending on how much & how effective your armor scheme is, you may need more Iridium from one playthrough to the next. As the Trade Guild sells not only unique artifacts but also information, and also may purchase unneeded artifacts from you, your need for Iridium may fluctuate. However, when advancing from the tutorial phase to the early game, a reserve of 10 Iridium should be kept to unlock trade & safe passage in Guild space.