Inside the sack, you find a set of oversized knuckle bones, carved with runes, an ancient tool for divination. The bones hum quietly and glow when you touch them. - Bogroot Demon (RPA-ADV6) 

White knuckle bones from another plane, and one of the six artifacts for unlocking Brizoor Waal.

Native to Hoshek: Plane of Life.

The Rune Bones, found in the Ancient Observatory, are revealed to be one of six keys for opening Brizoor Waal;

You hear a click, and then a grinding of gears. A door opens in the wall before you and leads you into an ancient durgolium chamber. The earth shakes, the air crackles with green energy, and you catch a whiff of summer breezes blowing through tall prairie grass. - Bogroot Demon (RPA-ADV6)

When traveling to Hoshek: Plane of Life, the Rune Bones are called to a Bone Golem;

In the midst of all this life, you spot a dead zone. A ring of wilt and rot, encircling a humanoid skeleton resting on a large stone plinth. Its bones are carved with runes that glow cobalt blue. Something about the skeleton transfixes you. - Gate of Brizoor Waal (RPA-ADVF)