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 Ocotloths per each planet in the game.

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. After the Alimbic send out a telepathic message promising the "Ultimate Power", however, Bounty Hunters from all over the universe begin heading to the Alimbic Cluster in hopes of finding it.

Samus Aran collects all eight of these ancient keys and defeats Gorea once and for all.