A cold sphere of obsidian
Though mostly dormant, the party discovered that the Orb became highly endothermic when in the presence of the white zombie dragon Szartharaax. The reasoning is unclear, as is the reason why Szartharaax grew in size and power toward the end of the fight.
Raven attempted to gain concordance with the Orb, and though he can’t tell if his attempts worked or not he has developed an intense fascination with the object and closely guards it, even from his own companions.
The Black Orb was pillaged from an ancient statue of the Demon Lord Orcus. The statue was found overlooking a shallow pit in the “Mines of Harken”http://www.obsidianportal.com/campaign/the-demon-prince/wikis/harkenwold-caverns, though the party was unable to detect any religious or arcane significance of the statue, location, or Orb itself. The statue was very out of place in the cavern, but whether it was transported there by the marauding goblins and hobgoblins or dug up from the room is as yet undetermined. The orb was discovered when the party toppled the statue into the adjacent pit, shattering it. Raven the vampire carefully extracted it with spare cloth, being careful not to touch it. He is the current custodian of the item.
The Orb is cold to touch but does not have any detectable aura or necrotic energy. A more careful analysis will be needed to determine its function.