Raritanium (Sargasso) are blue crystals that you will find during the game. To collect them you should smash them with your hammer. If you've been near some raritanium, it'll appear on your map. Raritanium can be used to upgrade your weapons (stat boosts and new abilities). To upgrade a weapon you must talk to Ms. Zurkon and navigate to the upgrades tab.
Index
All known locations on the map Sargasso
After defeating the Seekerpede.
To be able to get here you need to collect 30 Zurpstones and then you will be able to fly here on Trudi.
You will be able to get here during your second story visit to this planet.
