Raritanium as the name sugggests, was a rare and elusive substance that made a number of appearances in the Ratchet & Clank games. In Ratchet & Clank, Ratchet and Clank could obtain Raritanium from a driller on planet Hoven and trade it with Fred for the Persuader in the sewers of planet Pokitaru. It was said to be an excellent source of the substance until the Blarg began dumping their toxic waste into its oceans. In Going Commando, Raritanium could be drilled up in deserts and arctic plains using a special driller machine, or could be acquired throughout the course of space battles. It was used to purchase ship upgrades at Slim Cognito's Ship Shack.
In Tools of Destruction, you could use Raritanium to upgrade your weapons. Curiously, you could upgrade some weapons so that any enemies that were killed would give Raritanium, as well as bolts. In addition, if you collect 2,000,000 Raritanium in challenge mode, you can purchase the Golden Groovitron at the Device Vendor at the Cobalia Spaceport. In Ratchet & Clank: Up Your Arsenal, Clank's Director mentioned Raritanium after the Secret Agent Clank Holo-Vid was made.