WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks

Topic B Rock Cycle, Rock-Forming Minerals And Importance Of Rocks Analytical Type Questions

Question 1. Discuss some important rock-forming minerals.
Answer: Minerals are essentially elements or compounds naturally occurring in rocks. These have specific chemical bondage, and atomic structures and are crystalline. A mineral can also be a compound of several elements.

Silicon, oxygen, iron, aluminium, magnesium, calcium, sodium, and potassium are eight elements that form the best part of most rock-forming minerals.

A few of the mineral-identifying properties are hardness, specific gravity, colour, cleavage, crack, chemical composition, etc. A few of the minerals are discussed in detail as follows-

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Quartz:

The characteristics of quartz are as follows

  1. Nature: It is a hard mineral having hexagonal crystals. Rocks composed of quartz become very resistant to erosion.
  2. Colour: It is whitish in colour.
  3. Constituent rocks: Quartz is the main mineral of granite and basalt.
  4. Uses: Quartz is used to make ornaments and as a glass and stone cutter.

Feldspar:

The characteristics of feldspar are as follows

  1. Nature: It is smooth like a slate.
  2. Colour: It is white or pink in colour. The white variety is the Plagioclase Feldspar whose main chemical substance is sodium and the pink variety is Orthoclase Feldspar whose main chemical substance is potassium.
  3. Constituent rocks: Feldspar is another main mineral of granite and basalt.
  4. Uses: It is used in the ceramic industry and glass works for its smoothness.

Mica:

The characteristics of mica are as follows-

  1. Nature: It is lustrous, smooth, flaky and brittle.
  2. Colour: It may be white or black. The white variety is Muscovite and the black variety is Biotite.
  3. Constituent rocks: Mica is present in many rocks, Granite being one. The lustre of granite comes from mica
  4. Uses: Mica, being a bad conductor of heat and electricity, is used in preparing electrical goods. It is also used as decorative glitter and for making paint.

Gypsum:

Class 8 Geography Solutions WBBSE

The characteristics of gypsum are as follows

  1. Nature: It is soft and light.
  2. Colour: It is yellow in colour.
  3. Formation: It is a hydrated crystal of calcium sulphate.
  4. Uses: In the cement industry, in making fertilizers and construction works huge amount of gypsum is used.

Question 2. Discuss the types of soil produced from different rocks.
Answer: The given list shows different types of soil produced from various rocks-

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks Soil produced freom different rocks.

Question 3. List the different uses of the three kinds rocks in our daily lives.
Answer: Three kinds of rocks are used by us differently in our daily lives.

The uses are as follows

Igneous rocks:

The uses of igneous rocks are as follows

  1. Construction work is done using basalt and granite. For example- The temples of Rameswaram, Madurai, etc., are constructed from granite.
  2. Stone chips used in railway tracks are made from basalt. Basalt is also used in laying tram lines, constructing roads, and footpaths, and making utensils and statues.
  3. Granite is used to making floors, cooking-table tops, etc.
  4. Pestles used for grinding are made of basalt.

Sedimentary rocks:

Class 8 Geography Solutions WBBSE

The uses of sedimentary rocks are as follows

  1. Fossil fuels like coal, mineral oil and natural gas are available from sedimentary rocks.
  2. Limestone and dolomite (sedimentary rocks) are used in iron and steel industry, the chemical industry, as a raw material in cement-making and the construction of buildings.
  3. Mudstone is the basic ingredient of clay modelling or pottery.
  4. Rock salt from sedimentary rock layers is used as a cooking ingredient.
  5. Regions formed of these rocks contain a sufficient amount of groundwater because of their greater permeability.
  6. Silt, a product of sedimentary rocks, is very good for cultivation.
  7. Some sedimentary rocks are used in building palaces and castles. For example Red Fort in Delhi is built of sandstone.

Metamorphic rocks:

The uses of metamorphic rocks are as follows

  1. Valuable minerals like iron, copper, gold, silver, mica, manganese, etc., are obtained from these rocks.
  2. Erosive process in metamorphic rocks is very slow, these are used in various construction works.
  3. Slate is used to write on and also for making roof tiles. This is also used as a writing material.
  4. Marble is used in architectural works like building houses, temples, memorials, etc.
  5. Gneiss is used to build bridges and dams.
  6. Graphite, when metamorphosed to diamond, is used to make valuable jewellery.
  7. Amphi- bolite is used in constructing railway tracks.

Question 4. Discuss the importance and uses of rocks.
Answer: Economically rocks are very important. Some of the uses of rocks are

Architectural construction:

Various types of rocks are used to build temples, buildings, etc. For example, sandstone has been used to build the temple at Khajuraho and the dome at Sanchi.

Road construction:

Basalt is used for the construction of roads.

Groundwater retention:

The permeability of sedimentary rock layers helps in the preservation of groundwater. Areas formed. of granite also help in storing groundwater if there are cracks or faults on it.

Class 8 Geography Solutions WBBSE

Minerals Production:

Igneous and Minerals metamorphic rocks contain metallic minerals and sedimentary rock layers are rich in deposits of mineral oil, natural gas and coal which are later extracted for economic purposes.

Agricultural practice:

Rocks weather to form soil which is used for agricultural purposes.

Clay products:

Fire clay or heat-resistant clay and china clay are all products of mudstone. The inner lining of blast furnaces in iron and steel industry is done with fire clay. China clay is used in the manufacture of porcelain.

 

Topic B Rock Cycle, Rock-Forming Minerals And Importance Of Rocks  Short Analytical Type Questions

Question 1. Differentiate between rocks and minerals.
Answer: The differences between rocks and minerals are

Question 2. How does rock cycle work in nature?
Answer: Rock cycle is the process by which rocks of one kind change into another kind. It is the complete cyclic process of formation of rocks and their change from one type to the other. The speed of different stages of this cycle varies.

 

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks Rock Cycle

 

Igneous rocks are formed by the cooling and solidification of magma or lava. Sedimentary rocks are formed by erosion, transportation, deposition and consolidation of sediments broken from igneous rocks, other sedimentary rocks and metamorphic rocks.

Metamorphic rocks are formed due to heat and pressure exerted on igneous or sedimentary rocks and at times on metamorphic rocks as well.

All these rocks may be thrust deeper into the crust to become magma again under high temperature and pressure. Thus, we can conclude that this cycle of formation and transformation of rocks is a continuous process.

Class 8 Geography Solutions WBBSE

Question 3. Discuss the role of rocks in the formation of landforms.
Answer: Rocks contribute much to the process of formation of various landforms. For example-

 

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks Granite landforms

 

  1. The hills and mountains formed of granite rock undergo exfoliation. As a result, their eroded tops are dome-shaped.
  2. Basaltic plateaus are marked by their flat surfaces.
  3. Rivers flowing over limestone and dolomite surfaces produce potholes or depressions on the crust.
  4. Lava formed regions near the volcanoes have conical features.
  5. In the regions of sedimentary rocks, erosion gives rise to contrasting landforms. Hard, resistant rocks form higher or elevated lands while soft rocks turn into plains or lower plateaus due to constant erosion.

 

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks Basalt landforms

Question 4. Define karst topography. Write about the different types of karst landforms and give examples.
Answer:

Karst topography:

Karst topography is the landscape formed from the dissolution of limestone as a result of flowing river or rainwater. Carbonic acid (H2CO3) is produced when carbon dioxide (CO2) dissolves in rainwater and this reacts with limestone.

Due to this reaction, limestone erodes and forms various types of landforms.

Class 8 Geography Solutions WBBSE

Karst landforms:

The different types of karst landforms are as follows

  1. When a column of lime hangs from the ceiling of a limestone cave, it is called stalactite.
  2. When such a column rises from the floor of the limestone cave, it is called stalagmite.
  3. Stalactites and stalagmites join to form limestone pillars. Besides these, natural tunnels, natural bridges, terra rosa, lapies and sinkholes are also some examples of different types of karst landforms. Example-Some karst regions in India are Borra Guhalu, Andhra Pradesh, several caves in Mawsynram, cave in Tapkeshwar temple, Dehradun, caves in Panchmarhi, Madhya Pradesh.

 

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks Different types of Karst landforms

Question 5. How does soil form from rocks?
Answer: Over time, big boulders are broken up and transformed slowly into soil. This process of soil formation from rocks is called pedogenesis. The following stages are involved in soil formation-

Weathering of rocks:

Rocks are disinter- rated and decomposed through the processes of mechanical, chemical and biological weathering. The agents of erosion. such as rivers, winds, and glaciers breaking down rocks.

Addition of organic matter:

The organic matter gets mixed with the disintegrated and decomposed rocks in this stage.

Class 8 Geography Solutions WBBSE

Removal of particles:

Agents of erosion (rainwater, rivers, sea waves, etc.) also remove a portion of the broken rocks, in this stage.

Regolith formation:

Materials left behind after the process of removal of particles form loose debris on the earth’s crust called regolith. Regolith is the basic constituent of soil. The debris then interacts naturally with water, air and organic matter to form soil.

Question 6. Mention some of the uses of igneous rocks.
Answer:

Igneous rocks:

The uses of igneous rocks are as follows

  1. Construction work is done using basalt and granite. For example- The temples of Rameswaram, Madurai, etc., are constructed from granite.
  2. Stone chips used in railway tracks are made from basalt. Basalt is also used in laying tram lines, constructing roads, and footpaths, making utensils and statues.
  3. Granite is used to make floors, cooking-table tops, etc.
  4. Pestles used for grinding are made of basalt.

Question 7. Mention the uses of sedimentary rocks.
Answer:

Sedimentary rocks:

The uses of sedimentary rocks are as follows

  1. Fossil fuels like coal, mineral oil and natural gas are available from sedimentary rocks.
  2. Limestone and dolomite (sedimentary rocks) are used in iron and steel industry, chemical industry, as a raw materials in cement-making and construction of buildings.
  3. Mudstone is the basic ingredient of clay modeling or pottery.
  4. Rock salt from sedimentary rock layers is used as a cooking ingredient.
  5. Regions formed of these rocks contain sufficient amount of groundwater because of their greater permeability.
  6. Silt, a product of sedimentary rocks, is very good for cultivation.
  7. Some sedimentary rocks are used in building palaces and castles. Example Red Fort in Delhi is built of sandstone.

Question 8. Mention some of the uses of metamorphic rocks.
Answer:

WBBSE Class 8 Geography Chapter 8 Question Answer

Metamorphic rocks:

The uses of metamorphic rocks are as follows

  1. Valuable minerals like iron, copper, gold, silver, mica, manganese, etc., are obtained from these rocks.
  2. Erosive processes in metamorphic rocks being very slow, these are used in various construction works.
  3. Slate is used to write on and also for making roof tiles. This is also used as a writing material.
  4. Marble is used in architectural works like building houses, temples, memorials, etc.
  5. Gneiss is used to build bridges and dams.
  6. Graphite, when metamorphosed to diamond, is used to make valuable jewellery.
  7. Amphi- bolite is used in constructing railway tracks.

 

Topic B Rock Cycle, Rock-Forming Minerals And Importance Of Rocks Short Answer Type Questions

Question 1. Are rocks and minerals the same things? Give reasons for your answer.
Answer: No, rocks and minerals are not the same things. Rocks are homogeneous or heterogeneous aggregates of one or more minerals. A rock may contain one or more minerals.

Minerals are elements or compounds of several elements which are found in rocks. These have a chemical bondage, atomic structure and are crystalline.

Example-Granite and basalt are types of rocks, whereas, quartz and mica are types of minerals that are constituents of rocks.

Question 2. Why are landforms made of granite rock dome-shaped?
Answer: Magma which solidifies to form granite is viscous. As a result, the molten magma does not spread over extensive areas and solidifies in the shape of domes in earth’s interior.

Eventually, after repeated exfoliation these domes are exposed on the earth surface which further erodes to form rounded landforms. This type of landform is found in Malnad Plateau.

Question 3. Why is the Deccan Trap flat on the top?
Answer: The Deccan Trap, a part of the Peninsular Plateau of India, is formed of extrusive igneous rock-basalt. The lava that solidifies to form basalt is less viscous.

So the lava flow spreads over an extensive area before being solidified. As a result, the landform formed is flat-topped and not conical like hills or mountains.

Question 4. Which rocks are laid between and near a pair of railway tracks? Why are these rocks found here?
Answer: Basaltic igneous rocks are used between the railway tracks and these rocks are found here because these types of igneous rocks are formed of minerals like quartz, olivine, etc.

These minerals makes the rock very hard and resistant to erosion. The rock can withstand the pressure of the heavy trains, thus prevent the tracks from getting damaged.

WBBSE Class 8 Geography Chapter 8 Question Answer

Question 5. Why does a piece of granite glitter?
Answer: The chief mineral constituents of granite are quartz, feldspar and mica.Granite rocks glitter due to the presence of mica. At times, the crystalline structure of granite also helps the rock to glitter.

Question 6. Define Moh’s scale.
Answer: Moh’s Scale of Hardness determines hardness of minerals. This scale is graduated from 1-10. Talc is the softest mineral with a hardness value of only 1 on Moh’s Scale and diamond is the hardest mineral with a value of 10 on Moh’s Scale.

Question 7. What are minerals?
Answer: Elements or compounds that are crystalline, have well-defined atomic structure and chemical bondage and occur naturally in rocks are called minerals. Each mineral has its own shape, colour, hardness, and structure.

Example-Quartz.

Question 8. Why is Chotanagpur Plateau called the ‘Storehouse of minerals’?
Answer: The Chotanagpur Plateau has huge reserves of minerals like iron, copper, bauxite, manganese, dolomite, mica, etc. So, the Chotanagpur Plateau is called ‘Storehouse of minerals’ of India.

Question 9. Name a plateau region in India, other than Chotanagpur, that is rich in mineral deposits.
Answer: The Deccan Plateau is a mineral-rich region in India. It is a storehouse of various kinds of minerals. Ratnagiri and Chandrapur of this region have a good concentration of iron ore, coal, manganese, limestone, bauxite, chromite, etc. This region provides the maximum amount of manganese.

Question 10. Why is the soil formed from basalt rock black in colour?
Answer: Basalt is an extrusive igneous rock. The soil that is formed from this rock is black in colour as it contains titanium oxide and organic matter in sufficient quantity.

Question 11. Why is the soil formed from granite red in colour?
Answer: The soil formed from granite has more mineral content than organic matter and these minerals, which mostly contain iron oxide, make the soil red in colour.

Question 12. Why does clayey soil have high moisture-retention capacity?
Answer: Clayey soil is a mixture of silt and clay and their grains are so fine and compact that these form impermeable layers, which prevent loss of water. Hence, clayey soil has a high moisture-retention capacity.

Question 13. Which part of West Bengal has saline soil and why?
Answer: The mangrove region of the Sundarbans in the southern part of West Bengal has saline soil due to the entry of tidal seawater into the coastal area. This soil is ideal for growth of mangrove forests.

Question 14. What kind of rocks are mortar-pestle and slate-chalk?
Answer: Mortar is made of sandstone (sedimentary rock) and pestle is made of basalt (igneous rock). Slate is a metamorphic rock obtained from shale and chalk or the writing pencil on slate is limestone (sedimentary rock).

Topic B Rock Cycle, Rock-Forming Minerals And Importance Of Rocks Multiple Choice Questions Choose The Correct Option

Question 1. The hills of Chotanagpur Plateau are round-shaped because they are formed of

  1. Basalt
  2. Limestone
  3. Granite
  4. Sandstone

Answer: 3. Granite

Question 2. In basaltic regions, landforms are generally

  1. Flat-Topped
  2. Conical
  3. Rounded
  4. Dome-Shaped

Answer: 1. Flat-Topped

Question 3. Rising limestone columns from the ground of the limestone caves are called-

  1. Stalactite
  2. Pillars
  3. Stalagmite
  4. None of these

Answer: 3. Stalagmite

Question 4. The main constituent mineral of granite and basalt is-

  1. Gypsum
  2. Mica
  3. Quartz
  4. Olivine

Answer: 3. Quartz

WBBSE Class 8 Geography Chapter 8 Question Answer

Question 5. Pink-coloured orthoclase feldspar has the following basic ingredient-

  1. Calcium
  2. Potassium
  3. Sodium
  4. Silica

Answer: 2. Potassium

Question 6. The ceramic industry uses-

  1. Mica
  2. Dolomite
  3. Gold
  4. Feldspar

Answer: 4. Feldspar

Question 7. The scale used to measure hardness of minerals is the-

  1. Mercalli scale
  2. Richter scale
  3. Moh’s scale
  4. Gutenberg scale

Answer: 3. Moh’s scale

Question 8. The soil of sandstone regions are usually-

  1. Saline
  2. Acidic
  3. Alkaline
  4. Highly alkaline

Answer: 1. Saline

Question 9. Moh’s scale is graduated from-

  1. 1 to 10
  2. 1 to 5
  3. 1 to 12
  4. 1 to 100

Answer: 1. 1 to 10

 

Very Short Answer Type Questions Fill In The Blanks

Question 1. The cyclical process through which rocks transform from one type to another, is called ____________.
Answer: Rock cycle

Question 2. Round-shaped landforms result from ____________ rock.
Answer: Granite

Question 3. Mountain tops made up of basalt are ____________.
Answer: Flat

Question 4. Karst regions are composed of ____________.
Answer: Limestone

Question 5. The shape of crystals of quartz is ____________.
Answer: Hexagonal

Question 6. Orthoclase feldspar is ____________ in colour.
Answer: Pink

Question 7. The hydrated crystal of calcium sulphate is known as ____________.
Answer: Gypsum

Question 8. The main occupation of the people in Chotanagpur Plateau region is related to ____________.
Answer: Mine

WBBSE Class 8 Geography Chapter 8 Question Answer

Question 9. The loose debris formed from the weathering of rocks is known as ____________.
Answer: Regolith

Question 10. The stone chips used for construction of roofs are actually made of
Answer: Basalt

Question 11. In the case of ____________ soil, there is practically no relation between the soil and the parent rock.
Answer: Alluvial

 

Topic B Rock Cycle, Rock-Forming Minerals And Importance Of Rocks Write True Or False

Question 1. Minerals are compounds of basic organic materials of different types.
Answer: False

Question 2. Blackboards are made of quartzite.
Answer: False

Question 3. Karst landforms are found in areas of sandstone rock.
Answer: False

Question 4. Dams and reservoirs should not be built in limestone regions.
Answer: True

Question 5. Quartz is mostly used to cut glass and stone.
Answer: True

Question 6. The basic chemical in black plagioclase feldspar is sodium.
Answer: False

Question 7. Black mica is called biotite.
Answer: True

Question 8. Mica is a good conductor of heat and electricity.
Answer: False

Question 9. Gypsum is a moist crystal of calcium sulphate.
Answer: True

Question 10. The Chotanagpur Plateau is the storehouse of minerals in India.
Answer: True

Question 11. The soil formed from basalt has less capacity to hold moisture.
Answer: False

Question 12. Soil formed from granite is red in colour.
Answer: True

 

Match The Columns

1.WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks Match the following

Answer: 1. E, 2. C, 3. D, 4. B, 5. A

2.WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks Match the following 2

Answer: 1. D, 2. H, 3. A, 4. B, 5. E, 6. F, 7. G, 8. C

 

Topic B Rock Cycle, Rock-Forming Minerals And Importance Of Rocks Answer In One Or Two Words

Question 1. Which kind of rock constitutes the Chotanagpur region in India?
Answer: Granite.

Question 2. What are the limestone columns hanging down from the roof of a cave called?
Answer: Stalactite.

Question 3. Which region of India is known as the ‘storehouse of minerals’?
Answer: Chotanagpur Plateau.

Question 4. From which type of rock is black soil formed?
Answer: Basalt.

Question 5. From which rock is sandy soil formed?
Answer: Sandstone.

Question 6. What is the hardness value of topaz in Moh’s scale?
Answer: 8.

WBBSE Class 8 Geography Chapter 8 Question Answer

Question 7. Which mineral in Moh’s scale bears a hardness value of 10?
Answer: Diamond

Question 8. Which soil is the best for growing cotton?
Answer: Black soil or regur soil.

Question 9. Which kind of soil is found in the Sundarbans?
Answer: Saline soil.

Question 10. Name the most fertile soil.
Answer: Alluvial soil.

Question 11. Give an example of metamorphism in which a metamorphic rock is involved.
Answer: Formation of phyllite from slate.

 

Topic B Rock Cycle, Rock-Forming Minerals And Importance Of Rocks

Conceptual Questions And Answers

 

Who am I?

Question 1. ‘I am a constituent of the earth’s crust. I am composed of minerals.’-Who am I?
Answer: Rock

Question 2. ‘I am glittery, black or white. I am soft and malleable. I am a main constituent mineral of granite.’-Who am I?
Answer: Mica

Question 3. I have a smooth and attractive appearnace. I am used in making floors. I have been used in constructing famous architectural landmarks including the Victoria Memorial.’-Who am I?
Answer: Marble

Question 4. I am a very hard, fine-grained grey-black rock. I am commonly used in constructing roads. Water can easily pass through me.’- Who am I?
Answer: Basalt

Question 5. ‘I am that branch of science that deals with rocks and their characteristics.’-Who am I?
Answer: Petrology

 

Scrambled Words

1. ERLEDTIO
2. SPH ASYLABY
3. RTGEANI
4. NLEMSITE O
5. HMROTEA MC PI
6. PFLDEAS R
7. YLPRTEO GO
8. CTRSAITFAINOTI
9. DETPRTIOIE
10. M COGNELATORE

Answers:

1. DOLERITE
2. HYPABYSSAL
3. GRANITE
4. LIMESTONE
5. METAMORPHIC
6. FELDSPAR
7. PETROLOGY
8. STRATIFICATION
9. PERIDOTITE
10. CONGLOMERATE

 

Fill Up The Blanks In The Knowledge Hive

Question 1. Fill in the knowledge hive with information on basalt.

 

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks Fill the blanks

 

Answers:

  1. It is a volcanic igneous rock.
  2. It cools down rapidly.
  3. It is grey to black in colour.
  4. It is very heavy, hard and resistant to erosion.
  5. It is formed by quartz, feldspar, olivine and pyroxene.

 

Answer With Reference To The Illustration

Question 1. The schematic representation of rock cycle is given in the adjacent figure. Write the names of the rocks formed in the boxes marked 1, 2, and 3.

 

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks Illustration

 

Answers:

  1. Sedimentary rock
  2. Metamorphic rock
  3. Igneous rock

 

Crossword

 

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks crossword

CLUES

Down:

1. An example of a felsic rock.
3. Basalt is a rock.

Across:

2. It is widely used all over the world as a flooring material.
4. Common name of calcium carbonate.
5. ____ is used to make tram lines, roads, etc.

Answers:

Down: 1. Granite, 3. Volcanic
Across: 2. Marble, 4. Limestone, 5. Basalt

 

Topic B Rock Cycle, Rock-Forming Minerals And Importance Of Rocks Advanced Questions And Answers

Question 1. The Himalayas are formed of sedimentary rocks.- Justify.
Answer: Due to the pressure of overlying layers of silt and water, the sediments deposited in water bodies become compact and hard. So, the mountains that rise from these seas are basically formed of sedimentary rocks.

Thus the Himalayas, are formed of sedimentary rocks since these are young fold mountains risen from the Tethys sea. The Tethys was a shallow sea with silt deposited on its bed over the ages.

Question 2. Classify igneous rocks on the basis of their chemical composition.
Answer: Igneous rocks can be classified into four groups on the basis of their chemical composition.

These are-

  1. Acidic or felsic rock: This type of rock contains more than 65% silica. Examples- are granite, rhyolite, etc.
  2. Intermediate rock: The silica content of this rock is almost 55%-65%. Examples- andesite, diorite, etc.
  3. Basic or mafic rock: This type of rock contains 45%-55% of silica. Examples- are basalt, gabbro, etc.
  4. Ultrabasic or ultramafic rock: The silica content of these rocks is less than 45%. Example peridotite, obsidian, etc.

Question 3. What do you mean by palaeontology and mineralogy?
Answer: Scientists highly value the knowledge of fossils and a special branch dedicated to the scientific study of these has come into existence. This branch of science is known as palaeontology.

The branch of science that deals with all aspects of minerals in detail, is called mineralogy.

 

Topic B Rock Cycle, Rock-Forming Minerals And Importance Of Rocks Formative

 

Participation

This segment will indicate how much the students have actively participated and taken initiative during the class.

Various types of rocks with different features can be seen around us. On the basis of that, answer the following:

Question 1. What are the features which can be used to differentiate various kinds of rocks?
Answer: Colour of the rocks/ hardness of the rocks/ texture of the rocks/…

Question 2. Name the various kinds of rocks based on their features.
Answer: Igneous rocks/sedimentary rocks/metamorphic rocks/…

Question 3. Give a few examples of different types of rocks.
Answer: Granite/ sandstone/ limestone…

Question 4. What are the commonly used rocks in your day-to-day life?
Answer: Slate (writing boards)/ lead (used in pencils)…

 

Interpretation And Application

This segment will test whether the students have understood the topics, or whether they are just memorising them.

 

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks crossword.

 

CLUES

Down:

1. Molten rock material underneath the Asthenosphere
2. The type ofigneous rock that forms after lava reaches the earth’s surface
5. Metamorphic rock formed from Shale
7. A porous and light rock formed from the consolidation of volcanic shale

Across:

1. The rock used in making Taj Mahal
3. Igneous rock that forms dome-shaped landforms
4. The softest mineral
6. The rock laid between railway tracks
8. Flaky mineral used to make decorative glitters

 

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks crossword ..

 

Empathy And Cooperation

This segment will determine the ability of students to cooperate and help others within a group.

Question 1. Ask your friends if they have seen any monument made out of stone, while travelling. Make a list of such monuments. Do you know which stone they are made of? Find out and write down the type of stone from which these monuments are made and also their location. Try to find out how each type of stone was found at a particular location. Was the stone available in the local area or was it imported from another place?
Answer:

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks Friend, visit,seen

 

Aesthetics And Creativity

Question 1. Bring back some stones when you go for a trip. Discuss among yourselves and identify which rocks/minerals are they. Seek for the teacher’s help if necessary.
Answer:

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of Rocks minerals,rocks

 

Question 2. If there is an object or place of interest and a work of architecture in your surroundings, try and find out which rock it is made of.
Answer:

WBBSE Solutions For Class 8 Geography Chapter 3 Rocks Topic B Rock Cycle Rock Forming Minerals And Importance Of RocksResidential area, site of visit, rock

 

Question 3. If you have some pieces of rocks or minerals, expose them to some source of heat and observe which of them heats up faster or retains heat longer than the others.
Answer: Some rocks and minerals heat up quickly, while some others take much longer to heat up and retain the heat longer.

Rocks and minerals that heat up quickly- Granite, Quartz, Feldspar, Sandstone, Diorite, Gneiss

Rocks and minerals that retain heat longer- Basalt, Gypsum, Shale, Mudstone.

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