A contact metamorphic rock (see contact metamorphism) composed of calcium, magnesium, and iron silicates (with or without iron, copper, and manganese sulphides and oxides) which has been derived from limestone or dolomite by the metasomatic (see metasomatism) introduction of large amounts of silicon, aluminium, iron, and magnesium from a nearby igneous intrusion, usually a granite. Many skarns serve as host rocks for economic deposits of magnetite and copper sulphides.