A rather unusual wand core, which according to legend was used in Sir Cadogan’s blackthorn wand (Pm).
This and the troll leg umbrella stand in number twelve, Grimmauld Place, are the only references in canon to any part of a troll being used for anything other than, well, being part of a troll. Okay, that's not quite true. In the Ravenclaw welcome letter on Pottermore, Prefect Robert Hilliard suggests that some Ravenclaws might be exploring the possible magical uses of troll bogies, but he may not be entirely serious (Pm).
Tags: wand cores