Abstract: A particle concentrator and method of operation are disclosed wherein the concentrator includes a concentrator deck, preferably having an inverted frustoconical configuration with substantial portions of the deck being vertically inclined, an eccentric drive for producing rotary oscillating movement of the deck with low density and high density particle outlets respectively formed on an axially central portion of the deck and a peripheral portion of the deck. Riffle elements are angularly formed on the deck to facilitate particle separation with a mechanical stop limiting travel of the deck in a direction selected for propelling the higher density particles along the riffle elements toward the high density outlet. The concentrator may be operated either dry or submerged under standing liquid, with annular inclination of the deck, angular pitch of the riffle elements and height of the riffle elements on the concentrator deck being selected to facilitate classification and separation of the particles.