Abstract: A separation vessel (10) for separating materials of different densities comprising a chamber (14) having an external periphery (20A) at least part thereof which progressively increases from one section to another section. A mixture of materials of different densities enters the chamber (14) through an inlet (13) and travels in a spiralling vortex progressively outwardly to the widest section of the chamber (14). A primary exit (17) for material of greater density is provided closely adjacent to the widest section. A secondary exit (16) for material of lesser density is also provided.