The centrifugation increases the speed gravity separation of finely ground samples with heavy liquids. But contamination of the sink fraction by particles of the float fraction might occur when emptying the centrifugation tubes. A very simple, efficient and cheap device, preventing this disadvantage, is described here. In addition, it reduces appreciably the handling of the highly toxic heavy liquids. This device consists of a tube-funnel which is placed into the centrifugation tube. During the centrifugation the sink fraction falls to the bottom of the centrifugation tube through the funnel; this latter, containing the float fraction, is then closed with a PVC rod and is taken out of the centrifugation tube. This device has been used successfully for samples with a strong interlocking of opaque minerals and matrix or with thin coatings of opaque minerals on quartz grains, which made very fine grinding necessary.