skarn 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.

metasomatism Kind of metamorphism that involves the introduction of chemical constituents into a rock, or their removal from it (or both), via a volatile phase. Complete mineral transformations may occur, but the original rock texture may remain (resulting in a pseudomorph).