This stave might be the Stave of Equinex! The Stave of Equinex is actually a key, used to unlock the Equinex Monolith in the Ruins of Ravenwind, on the mainland west of the Dream Bough.
Find the four flames that still burn in those ruins: Samha, Imbel, Byltan, and Lahassa. Retrieve their essence and then while standing by the Equinex Monolith, use the essences to energize the stave. If this is truly is the Stave of Equinex, you will be able to unlock the Monolith and gather a sacred artifact from it.
Holding the energized stave is almost impossible. Its power rumbles through your body.
You reach out to the cold surface of the Equinex Monolith...
A small door opens, allowing you to reach in and take the artifact inside.
Beams of light fill the area around the Equinex Monolith.