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Introduction

We usually see the Earth from the outside. We see different types of landscape structures, plains, plateaus, grasslands, deserts, beaches, islands, forests or wildlife, etc. but have you ever wondered what can be found inside the Earth? All the things we see outside or use in our daily lives are formed because of the internal processes of the earth along with external factors. Here, we will be focusing on the inside of our Earth. We will learn about the rocks and minerals found inside our Earth, their uses, the classification of rocks, and various other related concepts. 

These rocks and minerals are very useful for us and are used in various processes and products. These notes will serve the needs of students who are looking for Class 7 Geography Chapter 3 notes. 


Rocks and Minerals

These are said to be building blocks of Earth which forms various kinds of landscapes on Earth as well as provide a number of resources as well. Rocks consist of minerals and these rocks are mined to extract minerals because these have Important properties and commercial value. There is no specific structure or chemical composition of rocks but minerals do have definite structure or other properties. Each rock can consist of one or more minerals. Rocks can be formed because of various geological processes and during these processes, various minerals get collected in one rock. When rocks are mined, these are called ores and the remaining rock after extraction of minerals is called tailing.


Uses of Rocks and Minerals

  • These are used in everyday life around us.

  • Rocks are used for making roads, buildings, and other construction purposes.

  • Some rocks which are precious are used as gemstones and some small rocks are also used in games as well.

  • Minerals are used for energy purposes such as coal, petroleum, etc. whereas others like fluorite, copper, talc, kaolinite, zinc, gold, diamond, etc. are used for making different kinds of products in the manufacturing industries from paper to jewellery products, minerals are used.

Difference Between Rocks and Minerals

Rocks

Minerals

It is an aggregate of one or more minerals or a structure of undifferentiated matter of minerals. 

It is a naturally occurring inorganic substance, element, or compound having an orderly structure and its own characteristics or properties.

It consists of minerals.

It doesn't consist of rocks.

They occur in solid forms.

They occur as mineral deposits.

They have different shapes or colours.

They have a definite shape or colour.


Classification of Rocks

The various types of rocks are mentioned below. 

Igneous Rocks

The rocks formed because of the solidification or cooling of the lava from the volcano are known as Igneous rocks. These are said to be the first and earliest rocks to be formed and other rocks are made from these rocks, thus these are also known as the primary rocks. These rocks are also considered magmatic rocks because of their formation from the magma or also called volcanic rocks because of the relationship with a volcano. These can be divided into the following two types:

  • Intrusive Igneous Rocks

These are those rocks that solidify under the crust of the Earth along with the presence of other existing rocks and it cools slowly and rocks become coarse-grained. The rocks which form deep in the crust and are coarse-grained are termed plutonic or abyssal rocks whereas the rocks which form under the crust but near the surface and are medium-grained are termed subvolcanic rocks or hypabyssal rocks.

  • Extrusive Igneous Rocks

The types of rocks which solidify above the crust of the Earth or on the surface outside are called extrusive Igneous rocks. Here, the process of cooking is not slow as compared to the intrusive one. They follow a quick solidification process because of the outside temperature present in the region thus, they are of fine quality and glassy texture.

Examples of Igneous Rocks


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The first image is of Basalt which is an example of extrusive Igneous rocks and is dark in colour and finely grained whereas the other image is of coarse-grained rock i.e Diorite which is an example of intrusive igneous rocks. Other examples are Dacite, Diabase, Gabbro, Obsidian, Granite, Peridotite, etc.


Sedimentary Rocks

These are the rocks that formed on or near the surface of the Earth because of geological processes such as erosion, weathering, dissolution, precipitation or lithification, etc. And usually have distinctive layers of bedding. They can be divided into three types:

  • Common Sedimentary Rocks

These sediments are carried in rivers or deposited in oceans or lakes and with time when the water disappears, the rock forms. Examples: sandstone, limestone, shale, etc.

  • Clastic Sedimentary Rocks

They are made up of clasts of the pre-existing rocks and the names of such rocks depend upon the size of the clast or grain.

  • Biologic Sedimentary Rocks

When a large number of living species die then such kinds of rocks form. Chert or limestone are formed in this way.


Examples of Sedimentary Rocks


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The first image is of limestone and another black one shale. Breccia, Chalk, Caliche, Chert, Conglomerate, Coal, Diatomite, Flint, limestone, etc. Are the other examples.


Metamorphic Rocks

These are the rocks that are formed from igneous or sedimentary rocks or even earlier metamorphic rocks which are formed due to high pressure, high heat, or other factors. The metamorphism process leads to the transformation of the existing rocks into another form. They are of three types:

  • Common Metamorphic Rocks

These include phyllite, schist, gneiss, quartzite, or marble.

  • Foliated Metamorphic Rocks

These are the rocks formed because of the parallel arrangement of certain minerals under pressure and are of platy or sheet-like structure.

  • Non- Foliated Metamorphic Rocks

They do not have platy or sheet-like structure and grains do not align even after having so much pressure.


Examples of Metamorphic Rocks


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The first image is of Gneiss and the other one is Anthracite. Other examples are Amphibolite, Hornfels, Marble, Lapis Lazuli, Novaculite, Quartzite, Soapstone, etc.


Rock Cycle

It is a cycle of various processes that lead to the formation and transformation of various types of rocks inside or outside the crust of the Earth. The three types of rocks which are formed are called igneous, sedimentary, and metamorphic due to various geological factors such as melting, cooling, heat or pressure, erosion, weathering, compacting and cementing, etc. When the heat and temperature inside the crust of the Earthrise, the magma forms which comes on the surface in the form of lava. When this lava hardened inside or outside the surface of the Earth becomes igneous rocks and when these igneous rocks erode into sediments because of various processes leads to the formation of sedimentary rocks and when these two rocks go under extreme pressure or other processes lead to the formation of metamorphic rocks which eventually are a transformation of already existing rocks.  These metamorphic rocks can be eroded further to form sedimentary rocks or can be melted into magma. Thus this cycle continues and these rocks go on the interchange from one type of rock to another. Our earth has several favourable conditions which lead to the formation or interchangeability of these rocks such as wind, water, tectonic plates, and their movements, heat or pressure, subduction, etc.

So, now we have covered the facts about Earth and have seen what does happen inside it. 


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Conclusion

Thus, here in this article, we have covered Chapter 3 of Class 7 Geography i.e. Inside our Earth. These notes will be useful for those who are in Class 7 or even the students of upper classes to understand the basic concepts. These will be helpful for those who find it difficult to read the chapter in the book and make notes out of it. Vedantu has eased your work by providing you with these crisp as well as comprehensive notes which will surely help you to understand the concepts properly as well as in revising the whole chapter quickly. You can check out notes of all other chapters or topics and other subjects as well on our website. These are created and prepared by the subject matter experts of Vedantu after thorough research to help you in your studies. We believe that these notes will surely help you to grow.

FAQs (Frequently Asked Questions)

1. What are Rocks and Minerals? Give Examples.

Answer. Rocks can be defined as an aggregate of one or more minerals or a structure of undifferentiated matter of minerals whereas minerals are naturally occurring inorganic substance, element, or a compound having an orderly structure and own characteristics or properties. Rocks consist of minerals and these rocks are mined to extract minerals because these have Important properties and commercial value. There is no specific structure or chemical composition of rocks but minerals do have definite structure or other properties. Each rock can consist of one or more minerals. Rocks can be formed because of various geological processes and during these processes, various minerals get collected in one rock. When rocks are mined, these are called ores and the remaining rock after extraction of minerals is called tailing. Examples of rocks are Granite, marble, basalt, etc. Whereas bauxite, cobalt, iron ore l, gold, etc. Are examples of minerals.

2. Write a Short Note on Types of Rocks.

Answer. There are three types of rocks found on Earth that continue to evolve from one type of rock to another. The rocks formed because of the solidification or cooling of the lava from the volcano are known as Igneous rocks. They are also called volcanic rocks, magmatic rocks, and primary rocks. Sedimentary Rocks are the rocks that formed on or near the surface of the Earth because of geological processes such as erosion, weathering, dissolution, precipitation or lithification, etc. Whereas These are the rocks that are formed from igneous or sedimentary rocks or even earlier metamorphic rocks which are formed due to high pressure, high heat, or other factors.

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