Gangue is generally an unwanted earthy material or impurity that is present in an ore. This can be found in ore deposits where the mineral is present. During the process of extraction, these impurities are mixed up with ore in the form of stone, sand, rock, etc.

The gangue must be separated from the mineral with the help of ore dressing or mineral dressing. Concentration of ore is one such process used to remove the impurities, which may depend on the physical and chemical properties. Example: Gravity separation and electromagnetic separation are some of the common methods which are used for the concentration of ore.