Rocks Types - Class VII Vistaar Advance

There are three major types of rocks : igneous rocks, sedimentary rocks and metamorphic rocks . Igneous Rocks :

(i) When the molten magma cools, it becomes solid. Rocks thus formed are called igneous rocks. They are also called primary rocks. There are two types of igneous rocks: intrusive rocks and extrusive rocks.

(ii) Lava coming out from the volcanoes is actually fiery red molten magma coming out from the interior of the earth on its surface.

(iii) W hen this molten lava comes on the earth's surface, it rapidly cools down and becomes solid. (iv) Rocks formed in such a way on the crust are called

extrusive igneous rocks.

(v) They have a very fine grained structure. For example, basalt.

(vi) The Deccan plateau is made up of basalt rocks. Sometimes the molten magma cools down deep inside the earth's crust.

(vii) Solid rocks so formed are called intrusive igneous rocks. Since they cool down slowly they form large grains.

(viii) Granite is an example of such a rock. grinding stones used to prepare paste/ powder of spices and grain are made of granite.

Sedimentary Rocks :

(i) Rocks roll down, crack and hit each other and are broken down into small fragments. These smaller particle are called sediments. These sediments are transported and deposited by wind, water, etc. These loose sediments are compressed and hardened to form layers of rocks.

(ii) These types of rocks are called sedimentary rocks. For example, sandstone is made from grains of sand. These rocks may also contain fossils of plants, animals and other micro- organisms that once lived on them.

(iii) Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure. For example, clay changes into slate and limestone into marble.

(iv) Rocks are very useful to us. The hard rocks are used for making roads, houses and buildings. Metamorphic Rocks

(i) The term 'metamorphic' is derived from the word 'metamorphosis'; which means 'change of form. (ii) W hen igneous or sendimentary rocks are subjected to extreme heat and pressure they undergo a complete change in their form and characteristics. Such rocks are called metamorphic rocks.

(iii) The change may occur as a result of volcanic activity, movements in the earth's crust or simply due to heat and pressure deep inside the earth. Marble, Slate, Gneiss and Quartzite are some examples of metamorphic rocks.

(iv) They have been formed from limestone, shale, granite and sandstone respectively.

ROCKS AND MINERALS ( a ) R oc k C y c l e

(i) One type of rock changes to another type under certain conditions in a cyclic manner.

(ii) This process of transformation of the rock from one to another is known as the rock cycle. When

the molten magma cools; it solidifies to become igneous rock.

(iii) These igneous rocks are broken down into small particles that are transported and deposited to form sedimentary rocks.

(iv) When the igneous and sedimentary rocks are subjected to heat and pressure they change into metamorphic rocks.

(v) The metamorphic rocks which are still under great heat and pressure melt down to form molten magma.

(vi) This molten magma again can cool down and solidify into igneous rocks.

( b ) Us e s of Roc ks a nd Min e ra ls

(i) Rocks are made up of different minerals. Minerals are naturally, occurring substances which have certain physical properties and definite chemical composition.

(ii) Minerals are very important to humankind. Some are used as fuels. For example, coal, natural gas and petroleum.

(iii) They are also used in industries - iron, aluminium, gold, uranium, in medicine, in fertilisers, etc.

( c ) Roc k D is t ribut ion in India

(i) Granite is found in Rajasthan, Madhya Pradesh, Chota Nagpur Plateau, Karnataka, Tamil Nadu, Andhra Pradesh and the Deccan trap region (Maharashtra).

(ii) Sandstone occurs in Vindhyachal and Aravali ranges. Limestone occurs widely in peninsular India. Coal mines occur in the basins of rivers Godavari, Mahanadi and Damodar, Marble is found in Rajasthan. The Indo-Ganetic plain is of sedimentary accumulation.

(iii) Rocks have great economic value. The cotton soil found in the Deccan trap is a product of extrusive igneous rocks. Other soils like alluvium are also result of disintegrated rocks. Stones used in construction of houses and roads, dams. etc. are all rock products. Rocks are source of precious and useful metals. Iron ore, bauxite, copper, lead, zinc and gold are found in igneous rocks. Non- metallic minerals include sulphur which is used for medicinal purposes. Coal and Petroleum are important sources of energy.

( d ) Flow Cha rt of Roc k Cy cle Cooling and Solidification MAGMA METAMORPHIC ROCK IGNEOUS ROCK SEDIMENTARY ROCK Weathering and Erosion Transportation of Eroded materials Deposition Consolidation, Compaction And Cementation Heating, Pressure and Chemical-action Heating and Melting Heating and Melting Heating, Pressure and Chemical-action Rock Cycle OBJ ECTIVE DPP- 2.1

1. Which of the following is correct? After metamorphism: (A) Granite changes to Graphite

(B) Limestone changes to Marble (C) Clay changes to Quartzite (D) Sandstone changes to Schist

2. Which of the following is called “Primary Rocks” and ‘Parent Rocks’ :

(A) Igneous Rocks (B) Sedimentary Rocks (C) Metamorphic Rocks (D) None of the above 3. Mineral fuels, coal & petroleum are found in :

(A) Igneous rocks (B) Sedimentary rocks (C) Metamorphic rocks (D) None of these

4. The uppermost layer over the earth surface is called :

(A) Sima (B) Crust

5. Where is the deepest mine in the world located ?

(A) India (B) South Africa

6. The main mineral constituents of the continental mass are :

(A) Silica and Alumina (B) Silica and Iron (C) Iron and Nickel (D) Silica and Nickel 7. Read the following :

1. The crust forms only 0.5 percent of the volume of earth .

2. 16 percent consist of the mantle. 3. 83 percent makes the core. Which is/are incorrect ?

(A) 1 (B) 2

8. The remains of the dead plants and animals trapped in the layers of rocks are called :

(A) Sediments (B) Fossils

9. The rock which is made up of molten magma called is:

(A) Igneous (B) Sedimentary

(i) Extrusive Igneous Rock (1) Granite (ii) Intrusive Igneous Rock (2) Sandstone (iii) Sedimentary Rock (3) Marble (iv) Metamorphic Rock (4) Basalt Answer Code :

(A) i - 1, ii - 2, iii - 3, iv - 4 (B) i - 4, ii - 1, iii - 2, iv - 3 (C) i - 4, ii - 3, iii - 2, iv - 1 (D) i - 1, ii - 4, iii - 3, iv - 2

11. Rocks which contain fossils are :

(A) Sedimentary (B) Metamorphic (C) Extrusive (D) Intrusive 12. The thinnest layer of the earth is :

(A) Crust (B) Mantle

13. Stated below are some statement :

(1) Sedimentary rocks are called secondary rocks (2) Sedimentary rocks are called stratified rocks (3) Sedimentary rocks are called primary rocks Which statement are true?

(A) 1 & 2 (B) 2 & 3 (C) 1 & 3 (D) 1, 2 & 3

14. The innermost layer of the interior of earth is also known as :

(A) Sima (B) Nife

SU BJ ECTI VE DPP-2.2

1. Explain the three layers of the earth? 2. What are the uses of rocks to us?

3. What is the state of the middle zone in the mantle? 4. What are sediments?

5. Why igneous rocks are called primary rocks? 6. Describe the interior of the earth explaining any one

layer in detail. Illustrate your answer with a diagram. 7. Explain the formation of different types of rocks? Give

examples of each.

8. What do you know about the rock cycle ? Explain with the help of a diagram.

9. Distinguish between the following : (i) Magma and lava

(ii) Rocks and ores

(iii) Metamorphic rocks and sedimentary rocks (iv) Intrusive and extrusive igneous rocks.

10. Discuss the "Rock Distribution in India" with a suitable map.

In document Class VII Vistaar Advance (Page 41-45)