Basic Concept of Metamorphic Rock

DEFINITION AND FORMATION:-

 Metamorphic rock is formed by ( the change the greek word 'metamorphosis' means change of form ) in a rock from its original form by heat and by pressure beneath the surface of the earth. The igneous and sedimentary rocks undergo a great change in their physical appearance and chemical properties due to (1) Intense heat and (2) Great pressure. Thus internal changes take place within the rocks. The particles are rearranged and redistributed affecting the structure and character of the rocks. The crystal in the rocks are arranged in fine parallel layer.

Sometimes, the change is so thorough that the original characters are no longer present in the altered rock.

EXAMPLES :-

Gneiss, Marble, Quartzite, Graphite, Slate, Amphibolite etc.are the example of metamorphic rocks. Under the process of metamorphism (1) Granite changes into gneiss, (2) Basalt into Amphibolite, (3) Limestone into marble, (4) Shale into slate, (5) Sandstone into Quartzite and (6) Peat coal into graphite.

Fig : Gneiss

Fig :- Structure of Graphite 

Fig :- Structure of Graphite

Fig :- Quartizite

Fig :- Slate

Fig :- Amphibolite

Fig :- Granite into Gneiss

Fig :- Basalt into Amphibolite

Fig :- Limestone into Marble

Fig :- Shale into Slate

METAMORPHISM :-

The greek word metamorphosis means change of form.The changes which take place in rocks due to intense heat and pressure is known as metamorphism.It is of two types : (1) Contact Metamorphism or local Metamorphism and (2) Regional Metamorphism.

CONTACT OR LOCAL METAMORPHISM :-

 When hot magma enters the fissures, it bakes the adjoining rocks in the contact zone.It produces chemical replacement and recrystallisation. As it affects by means of contact,it is know as contact metamorphism.As it also affects a small area, it is called local metamorphism.In this metamorphism,limestone is changed into marble.

REGIONAL METAMORPHISM :-

 Generally, it associates with great mountain building movements.Thus change which occurs,takes a long period and affects a large area.Hence,this is known as regional metamorphism.The pressure of the overlying rocks recrystallizes the rocks below.In this way, shale is changed into slate; and again state is changed to schist.

CHARACTERISTICS AND USES OF METAMORPHIC ROCKS :-

Metamorphic rocks are massive,completely crystalline and hard.They are resistant to erosion. They are very rich in minerals.they attract huge mining population.Since they are hard ,they are used as building and road materials.No fossil is found in metamorphic rock.when sedimentary rock undergoes changes,the fossils are destroyed by heat and pressure.