Gangue
The commercially worthless rock and mineral matter surrounding a valuable ore mineral.
Unit
Dimensionless
In depth
Gangue must be removed before smelting because heating it wastes fuel and it can contaminate the product. Physical concentration methods exploit differences in density, magnetism or surface wettability, and any remaining gangue is combined with a flux to form a removable slag.
Examples in the real world
Silica and clay accompanying metal sulfides; the sand removed from tin ore by gravity separation.