Bone Fragments

Bone Fragments are the remains of slain skeletal undead.

Source
Bone Fragments drop off any skeletal undead in Western Plaguelands, Eastern Plaguelands, Scholomance, and Stratholme.

Bone Fragments as a quest objective

 * Turn in 30 fragments to Rohan the Assassin for 1 Insignia of the Crusade
 * Repeatable version of the quest Bonescythe Digs