A vial of real human skull dust, leftover from carving pieces to make into rings, etc. Electroformed in copper with your choice of stone. 
This particular skull came from a closed Belgian monastery ossuary, and is estimated between 3-400 years old. 
*Human skulls and remains are perfectly legal to own! (At least in most states - sorry, no sales to GA, LA, or TN.)
Comes on a 24-inch antiqued copper chain.