NCERT Class 7 Geography Chapter 2: Inside our Earth Completes Notes Part 3

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Inside Our Earth

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Rocks

  • Earth’s Crust

  • Natural mass of matter that makes the crust

  • Differ in Size, Color & Texture

  • 3 Types of Rocks

    • Igneous

    • Sedimentary

    • Metamorphic

Now rocks are present on the earth crust and in simple terms if I want to define rocks I can say that they are natural masses of matter that makes up the outer crust or the upper crust of the earth. They can be differentiated on three categories the size of rock, the color of the rock and the texture of the rock. Again based on this categories we can defined three primary types of rocks. The Igneous, Sedimentary and Metamorphic. We will understand one by one in detail. Now the first rock is the Igneous rock.

Igneous Rocks

  • Molten Magma Cools & Solidifies

  • Also known as Primary Rocks

  • Two Types

    • Intrusive – Cools inside, Slowly cools, Forms Large grains - Granite

    • Extrusive – Comes on Surface – Basalt (Deccan Plateau) – Fine Grained

This Igneous rock is the result of the volcanic activity. So you have volcano that flows out and once this magma which is flowing out solidifies here. It would we known as the igneous rock. This Igneous rocks are also known as primary rocks and again most important factor here is to understand this igneous rocks could be of two types. They are either the Intrusive or Extrusive. As the name suggests Intrusive means they cool inside the earth surface so they are not visible on the earth crust so they move cool very slowly. They form larger particle size and common example of this is Granite which is found inside the earth crust. However there are certain rocks which come on to the surface and this deposit on the surface but they come out to be very fast and they are known as fine grained. They are kind of fine grained rock. They could be seen their common example is basalt. You can see basalt in Deccan Plateau. So that is known as igneous rock. So we have understood what is the Igneous rocks, how they are form the common example that is granite and basalt and basic classification for igneous rocks that is its of two types intrusive which is inside the earth and extrusive when it comes over the surface of the earth. The next rock is pretty interesting which is known as sedimentary rocks.

Sedimentary Rocks

  • Rocks roll, crack & hit to break

  • Sediments are transported

  • Then compressed & hardened

  • Sandstone – made from sand

  • Red Fort – red sandstone

  • Include fossils

Now what happens is when you have partials that flow on with river you have small particles that deposit towards the sites of the river or when you say there is wave action or wind action you have small deposition that occurs along the periphery of the agent with which they are moving as a result. They are kind of deposited for example sandstone is a common sedimentary rocks and this sandstone is made from sand commonly seen in desert areas. Now Red Fort in India is a common example. When we say it is made up of red sandstone. Now sense it is flowing with the agent which can be water, rain or waves any of the agents. It would include debris and it would also include kind of animal and plant fossils that could be seen. So fossils and debris is another important constituent of the sedimentary rocks that are seen. the next is Metamorphic Rocks.

Metamorphic Rocks

  • Igneous & Metamorphic change under heat & pressure

  • Clay Slate

  • Limestone Marble

  • Taj Mahal – White Marble

Now when both the igneous rock and the sedimentary rocks under high hit and temperature they are compressed for longer duration what happens is formation would result into a metamorphic rock. So metamorphic rock I can say is resultant from either igneous rock or sedimentary rocks. When they are lead under high temperature and pressure a common example is clay is converted into slate. Now this slate is an example of metamorphic rock. Limestone getting converted into marble and it is an example of metamorphic rocks. Again a common structure which is visible with marble that white marble is Taj Mahal. So Taj Mahal is made up of white marble from Makrana in Rajasthan. Now all this three rocks we have discuss but there is kind of cycle that operates. We have discuss that cycle in separate lecture that you can refer.