Jagged Scourgestone Piece

Just found 3 of these pieces, anyone know what they are for?

Bumping this up as I also would love to know!

Go speak to The Archivist for in-game clues.

I could only find jagged and broken, the one along the coast eludes me.

Go to the highest point of Captain’s Quarters in the northeast of the swamp. You’ll find the shattered scourgestone on the fighter there - the one I killed was called Hekkr Waverunner