volatile phases and metamorphism

• Magmas that cause contact metamorphism can be rich in volatile substances like water vapour and fluorine 

  • Where magma chambers encounters permeable rocks or strata that is fractured or jointed the volatiles escape into the country rock. 
• Metasomatism is reactions between volatiles and the rocks in the aureole that may form a range of unusual minerals. 

  • There is a change in chemical composition - metasomatism. 
• Metasomatism is an important process of metallic ore formation.