Rocks And Its Types

Geology :

·      Geology is the branch of earth science is concerned with the both the liquid and solid earth, the rock which it is composed and the process by which they changed overtime.

Petrology:

·      Petro means rock and logos mean study, so it is the branch of geology which deals with the study of rocks.

Rocks:

·      Rocks are defined as an aggregate of minerals.

Importance of Geology in Civil Engineering

·      It provides an opportunity to interpret the physical properties of individual rocks, likewise texture, structure, mineral and chemical composition etc...

·      These help in knowing the strength, durability, color, appearance etc.

·      These properties are very important for the civil engineer to know because different rocks are suitable for different purposes and no rock is ideal or best suited for all purpose.

Igneous Rocks:

·      All rocks that have formed from original hot molten material (magma) through the process of cooling and crystallization may be defined as igneous rock.

Difference between Magma and Lava

·      Magma: Magma is hot viscous siliceous melt containing gasses. It comes from greater depth below the earth’s surface. This melt remains within the surface.

·      Lava: when magma comes out upon the surface of earth, it is called lava.

Igneous rocks can be further divided into three sub-categories

·      Volcanic Rocks

      -Cooling and crystallization of lava.

      -Cools down very fast so the grain size of

       The crystal is very fine.

·      Plutonic Rock

         -This igneous rocks formed at

           Considerable depth of about 7 to 10

           Kilometer below the earth surface.

         -Slow rate of cooling so coarse

           Grained.

         -For Example: Granite

·      Hypabyssal Rocks

         - Also known as Sub Volcanic Rock.

         -Formed at intermediate depth, 2

           kilometers below the surface of

          Earth.

         -Mixed characteristics of volcanic

           And plutonic.

On The Basis Of Silica Content Igneous Rocks:

·      Acidic/Felsic Rock:

 -In these rocks silica content is more than 65%.

 -The light colored rocks are formed.

 -For example: Granite

·      Intermediate Rocks:

 -Silica content ranges from 55-65%.

 -Medium colored rocks are formed.

 -For example: Diorite

·      Mafic/Basic Rocks:

 - Silica content ranges from 45-55%.

 -Dark color rocks are formed.

 -For example:  Basalt

·      Ultra Mafic Rocks:

 -Silica content is less than 45%.

 -The ultra dark colored rocks are formed.

 -For example: Kimber lite

Texture of Igneous Rocks

There are three factors we define the texture of the igneous rocks

·      Degree of crystallization.

·      Granularity.

·      Fabric

Types of Texture

There are total five types of igneous rocks according to the texture:

1.  Equigranular Texture

2.  Inequigranular Texture

3.  Directive Texture

4.  Intergrowth Texture

5.  Intergranular Texture