Rocks and Rock Cycle

Answer the following questions

Question 1

Describe how Sedimentary Rocks and Igneous Rocks are formed. Give two examples of each.

Answer

The Sedimentary rocks are formed from material derived from the pre-existing rocks and from organic sources by the process of denudation. The eroded materials brought by rivers, streams, glaciers or wind are deposited in layers to form Sedimentary rocks. For Example — Limestone, Sandstone.

Igneous rocks are formed by solidification of molten magma that comes out from an active volcano. Hence, it is also known as primary rocks. For Example — Granite, Basalt.

Question 2

On the basis of occurrence, classify Igneous Rocks.

Answer

On the basis of occurrence, Igneous Rocks are of two types:

1. Intrusive Igneous Rocks — The rocks that are formed due to solidification of magma below the Earth's surface and remains surrounded by pre-existing rock are called Intrusive Igneous Rocks.
2. Extrusive Igneous Rocks — The rocks that are formed due to solidification of magma above the Earth's surface are called Extrusive Igneous Rocks.

Question 3

Name the three rock forming minerals.

Answer

Silicates, Quartz and Feldspars are three rock forming minerals.

Question 4

What are Batholiths?

Answer

Large mass of igneous rocks (chiefly composed of Granite) covering about 100 sq km area is called Batholiths. Its floor is not visible.

Question 5

What is Metamorphism? What are its causes?

Answer

Alteration of the minerals and textures of a rock by changes in temperature and pressure and by a gain or loss of chemical components to such an extent that the diagnostic features of the original rocks are modified is called metamorphism.

Following are the causes of metamorphism:

1. volcanic eruptions
2. the mountain building movements
3. endogenetic forces
4. contact with undergoing water

Question 6

Name a few important characteristics of Sedimentary Rocks.

Answer

A few important characteristics of Sedimentary Rocks are:

1. The material of sedimentary rock is derived from other pre-existing rocks.
2. They are layered rocks.
3. Sediments are deposited in sequential order i.e. size of sediments decrease from littoral margins to the centre of the water bodies.
4. Most of the sedimentary rocks are permeable and porous.
5. They contain fossils.

Question 7

Name the various types of Metamorphic Rocks.

Answer

The various types of metamorphic rocks are slate, schist, gneiss, quartzite, marble, amphibolite, meta-conglomerate and hornfel.

Question 8

Name the agents involved in the formation of sedimentary rocks.

Answer

The agents involved in the formation of sedimentary rocks are rivers, lakes, sea, glaciers, wind and organic materials. The processes of erosion, weathering, dissolution and lithification lead to formation of sedimentary rocks.

Question 9

Give examples of metamorphic rocks formed from igneous and sedimentary rocks.

Answer

Metamorphic rocks formed from igneous rocks — Gniess from granite, Schist from Basalt

Metamorphic rocks formed from sedimentary rocks — Marble from limestone, Quartzite from Sandstone.

Question 10

What are Sills and Dykes?

Answer

Sills— It is sheet like body of igneous rock. It is formed when magma forces its way between two layers of sedimentary rocks and cools and solidifies there.

Dykes— It is sheet like body of intrusive igneous rock. When magma is forced upwards, it fills vertical cracks or fissures in existing rock and it hardens there to form dykes.

Question 11

Why are sedimentary rocks also called stratified rocks?

Answer

Sedimentary rocks are formed by deposition of sediments in layers in beds of water bodies or on earth's surface (if brought by wind). They are deposited in layers, therefore, they are known as stratified rocks and layers are called strata.

Question 12

What processes are involved in the formation of igneous rocks?

Answer

The processes involved in the formation of igneous rocks are cooling, solidification and crystallization.

Question 13

What is a Rock Cycle?

Answer

A cyclic process of changing the form of rocks is called Rock cycle. It represents the interrelationships among the three rock-forming processes: igneous, sedimentary and metamorphic.

Question 14

What are the rocks?

Answer

An assemblage of minerals bound together that form a more or less definite unit of the Earth's crust is called rocks.

Question 15

Classify the rocks on the basis of their origin.

Answer

On the basis of their origin, rocks are of three types:

1. Igneous rocks
2. Sedimentary rocks
3. Metamorphic rocks

Question 16

What is meant by intrusive rocks?

Answer

Magma that solidifies below the Earth's surface and remains surrounded by the pre-existing rock is called intrusive rocks. For example, granite.

Question 17

What are extrusive rocks?

Answer

The rocks that are formed due to solidification of magma on the Earth's surface are called Extrusive Igneous Rocks. For example, Obsidian.

Question 18

How important are rocks for industrial development?

Answer

The importance of rocks in industrial development are:

1. Rocks contain minerals called ores which are used for extracting metals and non-metals.
2. They provide fossil fuels like coal and petroleum.
3. The entire automobile industry uses petrol for their transport system.
4. They provide raw material for manufacturing industries like limestone and gypsum are needed by cement industry.
5. They are used as building materials. For example, granite and marble.

Define the following terms

Question 1

Minerals

Answer

Minerals are naturally occuring, homogenous solid inorganic substance that has a definite chemical composition with its own chemical and physical properties.

Question 2

Rocks

Answer

Rock can be defined as an aggregate of minerals that form a more or less definite unit of the earth's crust.

Question 3

Sills

Answer

A sheet like body of igneous rock that is formed when magma forces its way between two layers of sedimentary rocks and cools and solidifies there is called Sills.

Question 4

Dykes

Answer

A sheet like body of intrusive igneous rock which is formed when magma is forced upwards, it fills vertical cracks or fissures in existing rock is called Dykes.

Question 5

Conglomerate

Answer

Conglomerate is a type of mechanically formed sedimentary rock which consists of rounded or sub-rounded fragments, usually water-born cobbles, pebble and gravel, cemented together by a matrix of calcium carbonate, silica, etc.

Distinguish between the following terms

Question 1

Rocks and Minerals

Answer

Question 2

Volcanic rocks and plutonic rocks

Answer

Question 3

Thermal and Dynamic Metamorphism

Answer

Give reasons for the following

Question 1

Igneous rocks are also called primary rocks.

Answer

Igneous rocks are also called primary rocks because they are formed when molten lava solidifies. Sedimentary rocks and metamorphic rocks are formed from other rocks.

Question 2

Extrusive igneous rocks have generally small crystals.

Answer

Extrusive igneous rocks have generally small crystals because they cool rapidly to solidify. The crystals do not have much time to form until the rock cools all the way, which stops the crystal growth.

Question 3

Rocks are of great economic significance.

Answer

Rocks are of great economic significance because they provide us with various minerals, fossil fuels, building materials and precious metals etc.

Question 4

Lithosphere is called rocksphere

Answer

The Lithosphere is the outermost layer of the Earth's crust that is made up of solid rocks, including igneous and sedimentary rocks. In Greek, Litho means rock or stone. Thus, Lithosphere is also called rocksphere.

Question 5

No fossil is found in metamorphic rock.

Answer

Metamorphic rocks are formed due to change in texture and mineral composition of the pre-existing rocks. During this process of change, the fossils of original sedimentary rocks are destroyed and therefore no fossil is found in metamorphic rocks.

Diagram

Question 1

Draw a diagram of a volcano and igneous rocks.

Answer

Below diagram shows a volcano and igneous rocks:

Question 2

Draw a neat diagram to show the rock cycle.

Answer

Below diagram shows the rock cycle:

Choose the correct options

Question 1

Which of the following rocks is also called parent rock?

1. Sedimentary Rock
2. Igneous Rock
3. Metamorphic Rock
4. None of the above

Answer

Igneous Rock

Question 2

Which type of rock is Granite?

1. Sedimentary Rock
2. Intrusive Igneous Rock
3. Metamorphic Rock
4. Extrusive Igneous Rock

Answer

Intrusive Igneous Rock

Question 3

Which of the following statements related to extrusive igneous rock is correct?

1. They are formed below the earth surface
2. They have fine crystals
3. Limestone is the best example of this rock
4. They are formed by the slow cooling of magma

Answer

They have fine crystals

Question 4

Which of the following is the metamorphosed form of Sandstone?

1. Slate
2. Gneiss
3. Quartzite
4. Marble

Answer

Quartzite

Question 5

Which of the following rocks consists of rounded; fragments, formed by cementation process?

1. Sandstone
2. Conglomerates
3. Claystone
4. Limestone

Answer

Conglomerates

Question 6

Sedimentary rocks are called stratified rocks as

1. They are formed by the accumulation of lava
2. They are formed by the decomposition of rocks
3. They are deposited in layers
4. They are foliated

Answer

They are deposited in layers

Question 7

Which of the following statements is correct?

1. Igneous rocks are generally pervious in nature.
2. Sedimentary rocks have pore spaces.
3. Foliation is observed in igneous rocks.
4. Fossils are found in igneous rocks.

Answer

Sedimentary rocks have pore spaces.

Question 8

Which type of rock is chalk?

1. Chemically formed sedimentary rock
2. Carbonaceous Rocks
3. Calcareous rocks
4. Clastic sedimentary rock

Answer

Calcareous rocks

Question 9

Which factor is responsible for the formation metamorphic rocks?

1. Duration of daylight
2. Heat & pressure
3. Weathering
4. None of the above

Answer

Heat & pressure

Question 10

Which of following is the mechanically formed sedimentary rock?

1. Limestone
2. Dolomite
3. Sandstone
4. Chert

Answer

Sandstone

Question 11

The cyclic process of changing the form of rocks is called

1. Natural cycle
2. Rock cycle
3. Stone cycle
4. Metamorohism

Answer

Rock cycle

Question 12

Which of the following is the example of metamorphic rock?

1. Sandstone
2. Gneiss
3. Chalk
4. Granite

Answer

Gneiss

Question 13

Which of the following process is responsible for the formation of igneous rocks?

1. Sedimentation
2. Metamorphism
3. Cooling & solidification of magma
4. Lithification

Answer

Cooling & solidification of magma