Bloodstone Choker

Bloodstone Choker is a quest item. It was a possesion of Gakin the Darkbinder before Surena Caledon stole it and joined the Defias Brotherhood. The choker is used to summon a Voildwalker in the quest  at the Summoning Circle, in one of the crypts underneath the Slaughtered Lamb.

Source
This item is provided for the Alliance warlock quest.