4th Class Science Rocks and Soil Introduction

Introduction

Category : 4th Class

*     Introduction

 

The earth as we see it is made up of rocks, soil, and minerals.

                                   

                  Rocks                                                                 Soil                                                     Minerals  

The lower layers of the soil are the rocks. If you observe a rock closely you wilt see small grains on it. A single rock may have grains of different colour. These grains are the minerals occurring naturally. Many rocks that contain metals are called ores. We get iron, copper, aluminium from their respective ores. Gemstones are the minerals in the form of crystals e.g. diamond, emeralds, rubies etc. Soil is the uppermost layer of the earth's surface. Soil is responsible for the greenery and life on the earth's surface. It supports the plants, which produces food for the entire living world. Soil is also home to many microorganisms and insects. There are different kinds of soil. Sandy soil, clayey soil and loamy soil.

 

*       Types of Rocks and Their Uses

Our earth is made up of rocks. There are 3 kinds of rocks. They are:

(a) Igneous rocks

(b) Sedimentary rocks

(c) Metamorphic rocks

 

*           Igneous Rocks

Igneous rocks are formed from the molten rock material. The hot liquid material comes out on the earth surface, from deep inside the earth, through cracks and then cools down. These rocks contain minerals such as quartz, mica, silica, iron etc. Granite and pumice are two important type of igneous rocks.

         Igneous Rock  

 

*           Sedimentary Rocks

Sedimentary rocks are formed by splitting up of materials, such as gravels and pebbles, by wind, water and snow of the surface of the soil. As the materials pile up on the top, the pressure hardens the lower layer and converts it into rocks. For example sandstone and limestone.

     

            Sedemonary Rock  

 

*         Metamorphic Rocks

Metamorphic rocks are formed by the action of heat and pressure on clay rocks. They are rocks that have gone through changes. As the name suggests metamorphic means change. These rocks were originally sedimentary or igneous rocks. The changes make them tougher and harder, for example slate and marble.

      Metamorphic Rock      

 

 

common.jpg  

 

    How many kinds of rocks are there?

(a) 5 kinds

(b) 2 kinds

(c) 10 kinds

(d) 8 kinds

(e) 3 kinds

 

Answer: (e)

 

 

     Pumice is an example of which one of the following kind of rocks?

(a) Sedimentary rocks

(b) Metamorphic rocks

(c) Igneous rocks

(d) Both (a) and (b)

(e) None of these

 

Answer: (c)

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