Rocks - The Concept, Types and Uses| CTET |

 Rocks - Meaning - Types- Characteristics - Uses

                 ROCKS

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         Rocks are  Solid materials of  the Earth's Crust. It may hard or soft. They are of different composition size, texture and colours. 

       Rocks also include loose materials such as sand and silt. 

 Rocks are made up of one or more minerals but they do not have a definite chemical composition. 

                              TYPES

On the basis of formation rocks are of three types

              1.  Igneous Rocks

              2.  Sedimentary Rocks

              3.  Metamorphic Rocks

      IGNEOUS ROCKS

i) The term igneous derived from the Latin word            'ignis' - which means 'fire' . 

ii) Deep below the earth's, rocks are in a molten  state called Magma.when magma cools and solidifies, it forms a very hard rock known as igneous rocks. 

iii) There are two types of formation of igneous rocks

     a.  Extrusive igneous rock formation

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                When the molten lava comes on Earth's  Surface and cools down rapidly on the                            crust , forms extrusive igneous rocks. 

      b.   Intrusive igneous rocks formation

                                   ⬇

        When molten magma cools down deep inside the earth's crust, the cooling process is slow and the rocks are called intrusive igneous rocks. 

               

Characteristics:-

i) Igneous rocks are called primary rocks because other types of rocks are formed from these rocks. 

ii) These rocks are hard and compact. They are impervious rocks and do not contain the remains of animals and plants. 

iii) Basalt, Granite, dolorite etc are ex of igneous rocks. 

   SEDIMENTARY ROCKS

i) The word ' Sedimentary' derived from the Latin word Sedimenter which means ' Settle down'. 

ii) Sedimentary rock is a type of rock formed by the deposition and hardening of layers of sediment. 

iii) These rocks are generally formed under water. 

iv) Sand Stone, limestone, shale, gravel, clay and conglomerate are the examples of sedimentary rock. 

Characteristics:-

i)  Sedimentary rocks are softer than igneous rocks. 

ii) These rocks contains fossils of plants and animals. Petroleum  and coal occurred in sedimentary rock. 

iii) these rocks constitute 70% of all rocks found on the surface of earth. 

METAMORPHIC ROCKS

i) The word metamorphic means change  of form. 

ii) These rocks formed when igneous and sedimentary rocks get changed due to heat and pressure. 

iii) Marble ( made from limestone),  Slate ( formed from shale) ,quartzite ( from sandstone) and Gneiss are example of metamorphic rocks. 

Characteristics:-

Metamorphic rocks are hard and take a long time in its formation. They are harder than the other rocks. 

                           Extra Facts 

  What is the difference between Magma and      Lava  ?? 

     Magma is the molten rocks that is in the underground  and Lava is molten rocks  that breaks through the Earth's  surface. 

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