Yharnam Stone is a Key Item in Bloodborne.
|A sacred heirloom left by Yharnam, Pthumerian Queen.
"The Queen lies dead, but her horrific consciousness is only asleep, and it stirs in unsettling motions."
- No further use than proving your accomplishment.
- Drops from Yharnam, Blood Queen of the Old Labyrinth
- Stays in your inventory when moving to NG+
One could reasonably assume that this is a so called Lithopedion, a calcified, unborn, dead fetus.