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)