Soul Scavenger, Heart of Stone, is a Unique Primordial Scavenger found in the Pandemonium Fortress Level 1 in Act V of Diablo III. It spawns for the Demon Souls event, and killing it is required to free the trapped souls.
In combat, it has Reflects Damage and Orbiter affixes.
Visually, Soul Scavenger has a different and unique coloring. It is also the only Primordial Scavenger that can be found outside the Battlefields of Eternity.