Octolith

An Octolith is a crystal of unknown material that contains the essence of Alimbic elders. There are eight of them in total, and all are required to gain access to the Oubliette. There are two Octoliths per each planet in the game. The eight Octoliths power the Alimbic Cannon, located on Alinos, which summons the Oubliette that contains Gorea.

Metroid Prime Hunters
They are left dormant for some time, it is unknown if anyone had attempted to acquire the crystals in the years before the events of Metroid Prime Hunters. Shortly after the events of Metroid Prime a telepathic message originating in the Alimbic Cluster is sent out to many powerful beings and governments promising the "Ultimate Power", soon Bounty Hunters from all over the universe begin heading to the Alimbic Cluster in hopes of finding it. The Galactic Federation sent out Samus Aran, their most prized warrior, to either secure the power, or failing that, destroy it.

Samus soon learns after arriving at the Celestial Archives that the Octoliths are vital to reaching the "Ultimate Power" and collects all eight of these ancient keys and returns to Alinos, activating the Alimbic Cannon. The Oubliette appeared in the center of the Cluster and Samus headed off to defeats Gorea once and for all. She gained the Omega Cannon in her second battle with the creature, and with this weapon, rid the universe of Gorea's threat.

Whether the "Ultimate Power" spoke of was the Omega Cannon she used to defeat Gorea or Gorea itself is unknown, as both were significant and powerful to the Alimbic, as well as conveniently in the same place.