igneous petrology

                                                                       UNIT – I

Igneous Petrology.

Rock : It is on Aggregate of minerals.

Minerals: It is defined as homogeneous substance having definite chemical composition, definite Atomic structure and formed due to inorganic process of nature is called mineral.

 Petrology : study of Rocks is called petrology.

Mineralogy : study of minerals is called mineralogy.

Pyrogentic minerals : minerals which are formed from the magma by the process of crystallization are known as pyrogentic minerals.

Rock forming minerals : 99.9 % of the earth crust is made up of some twenty minerals as these minerals are most abundant constituent of rock of all types are called Rock forming minerals.

Magma : It is hot molten material mainly silicates

Lava : when magma comes on surface is called LAVA.

Igneous Rock : Are those rocks which formed by solidification or crystallization of hot liquid melt known as magma is called Igneous Rock. The various Rock that occur on the surface of the earth are divided into three classes according to their origin

A.   Primary or Igneous Rock

B.   Secondary or Sedimentary Rock

C.   Metamorphic Rock

Why magma generate from time to time –

a) Temp within earth increases regularly with depth .

b) Radioactive disintegration.

c) Earth Movement.

Once magma generate why it starts to move surface –

a) It is lighter than surrounding rock.

b) It contains great quantity of gases.

c) It is under great pressure due to overlying load.

  

Mineral composition of Igneous Rock : 

Magma consists of eight elements make nearly 99 %  0, Si, Al, Fe, Mg, Ca, Na, K, during cooling processes these elements crystallizes and give a minerals.

Intrusion : - 

The movement of magma within the rock is known as intrusion and magma which the rock below the earth give rise to Intrusive Igneous Rock or Plutonic Rock.

Extrusion : -

When magma comes to surface it is called lava and solidified  on surface it is called Extrusion and extrusive Igneous Rock or Volcanic Rock

If magma solidified in between intrusion or extrusion is called Hypabyssal Rock.

Above 3 class of rock are classified depend on origin , or mode of occurrence of magma.