Dense media separation (DMS) is a process where a feed consisting of valuable and waste particles can be separated in a bath of "heavy liquid." The basic principle is that the liquid has a specific gravity that is between that of the valuable and waste particles. Thus, the lighter component floats in the liquid, while the heavier component sinks. To make the heavy liquid, a suspension of dense powder (e.g., magnetite) in water is typically used; adding more or less powder increases or decreases the specific gravity of the liquid. The ideal specific gravity of the liquid is called the "cut point" and this is where the separation efficiency is greatest (i.e., recovery of the valuable mineral and rejection of the waste minerals is optimum.)

DMS is used in many processing circuits including for coal, diamonds and some metal ores. In many cases, the separation is actually done in a hydrocyclone. For example, in some diamond operations, the crushed ore is mixed with a liquid that has a specific gravity similar to that of the diamonds (which are relatively heavy compared to the gangue minerals.) While the diamonds sink to the bottom of the hydrocyclone and leave as "underflow," the less dense waste is pushed to the top of the equipment and leaves as "overflow."