What happens when limestone undergoes contact metamorphism?
It depends how pure the limestone is. A pure limestone will be transformed into a marble which involves a change in the calcite crystal texture but no significant change in chemistry. Impure limestones can be transformed in a number of different ways. A dolomitic limestone will contain periclase or brucite as the carbonate associated with magnesium ions is driven off. If the dolomitic limestone contains small quantities of silica, then a forsterite marble can be formed in which the magnesium end member of olivine is formed; this rock often has a slight green colour. Where clays are present, there is the possibility of other different minerals forming alongside calcite depending on the temperature and pressure of formation but also the exact chemistry of the impurity. Such minerals may be epidote, wollastonite, diopside, albite and actinolite. These minerals are invariably calcium bearing silicates.
