The device has a belt conveyor (10) with several spaced-out belts (11). There is a separating drum (13) located at the delivery end of the conveyor and faced with piercing elements (14). An axially parallel yielding counter-pressure drum (15) with an elastic casing is positioned so that the hard stone elements can pass through the gap formed by the separating drum and counter-pressure roller and foreign objects are pierced by the elements on the separating drum.
