Cursed Sourcestone is a currency for level 25 armor and planar items.
It it used to purchase Gloves, Greater Planar Essence, or Chest of Planarite.
The loot table is the following:
(1) Chest : [Chest of Planarite]
(2) Greater Planar Essence: [Cauterizing Crystal] [Smoldering Planar Condensate] [Magnatite Focusing Crystal]
(1) Gloves: [Planar Chain Gauntlets] [Planar Gloves] [Planar Leather Gloves] [Reinforced Planar Gauntlets] [Planar Gauntlets]
The easiest way of purchasing these from first entering the zone is at the vendor at Scarwood Lift Base. This is in the center of the south of the zone.