METAMORPHIC ROCKS

           METAMORPHIC ROCKS
The word metamorphic has been derived from two Greek words 'Meta' which means change and Morph' meaning form. Thus, metamorphic rocks are formed when the orginal character of the igneous and sedimentary rocks- their colour, hardness, texture, and mineral composition is partly or wholly changed. These changes take place under favourable conditions of heat and pressure.

Metamorphism can occur in both sedimentary and igneous rocks.  The main feature of the origin and formation of metamorphic rock is that during this (due to the influence of internal and external forces, the organization and appearance of the rock changes, but some kind of change in the rock disintegration and separation do not occur.
Many rocks change so much under extreme heat or pressure that it becomes difficult to know their true form.  Metamorphic rocks are identified by their hardness, dense structure and interlocked ravines.  The following classification of conversion is done on the basis of means of conversion and area of ​​influence:

1. Metamorphism on the basis of Agency. This type of metamorphism is caused by dynamic and thermal agencies. 

(a) Dynamic Metamorphism. This type of metamorphism is caused by pressure. As a result of pressure, granite is converted into gneiss; clay and shale are transformed into schist at great depths of the earth's crust. Both these rocks are commonly found over large parts of South India and in some parts of Assam, West Bengal, Jharkhand, Orissa, Madhya Pradesh, Chhattisgarh and Rajasthan. 

(b)Thermal metamorphism is the conversion of heat due to thermal effects.  This type of conversion makes quartzite from sandstone and slate from clay and rock.  Ordinary coal is converted into andesite and graphite, similarly lime stone becomes marble.  All these changes occur from about 50 ° to 80 ° C.  At temperatures from 150 ° to 200 ° C, the slate converts more into phyllite. 

2. Metamorphism on the basis of Zone of Influence. On this basis the metamorphism is  of two types
(a).Regional Metamorphism - When high temperatures and pressures at high depths change the rocks of a large area, it is called regional metamorphism.  Quartzite is formed in this way.  It is one of the hardest rocks that make up the mountain  and ridges.
(b) Contact Metamorphism. This is just likethermal metamorphism. In areas of mountain-building or of vulcanism, molten matter may be injected into the existing rocks even close to the surface. Such a contact with heat over a limited area of about 2 km from the intrusion brings about a change in rocks under temperatures ranging from 50°C to 800°C. Some such reason is responsible for the peak of Mount Everest consisting of metamorphosed .