Skarn is a metamorphic rock that has been chemically and mineralogically altered by metasomatism. Metasomatism is the alteration of rocks by hot, chemically-active fluids that flow or diffuse through the rocks and cause recrystallization and compositional change.


Skarn commonly forms around the edges of a magma body that intrudes a nearby rock mass. Rocks formed or altered by the interaction of magma, country rock, reactive fluids and heat are known as skarn. Other environments of metasomatic activity are also known to produce skarn.

Most skarns form when carbonate rocks such as limestone, dolostone or marble are intruded by a magma body and altered by contact metamorphism and metasomatism. At the time of intrusion, the heat of contact metamorphism is the primary agent of change.


as the magma cools, it releases hot, acidic, silicate-rich fluids. Some magmas contain up to several percent dissolved water on the basis of weight, but because of the specific gravity difference between water and magma, the volume percent of dissolved water is at least twice the weight percent. When this water is expelled from the magma, it is a solvent that has the ability to carry heat and chemically-active solutes into the country rock.


Many different types of rock can be transformed into skarn by metasomatism. The original rock that is altered is known as the "protolith". Although carbonate rock is the most common protolith, many skarns have formed in granite, basalt, conglomerate, tuff, shale and other types of rock.
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