Abstract: An apparatus is provided for classifying and separating larger or more dense particles from fine particulate material entrained in a stream of air. The apparatus has a helically-shaped air chamber with a truncated frusto-conically shaped circumferential periphery. A series of extraction ports are disposed at spaced intervals along the truncated apex of the periphery. An adjustable blade means disposed at each extraction port segregates the outer fraction of particles from the air stream and diverts it into an extraction chamber surrounding the extraction port. The extraction chamber is pressurized to prevent the outflow of air from the helically-shaped air chamber through the extraction port and to remove the extracted particles to a collection point for further processing.