WBBSE Solutions For Class 7 Geography Chapter 6 Rock And Soil Topic A Rock

WBBSE Chapter 6 Rock And Soil Topic A Rock Long Question And Answers

Question 1. State the differences between rocks and minerals.
Answer:

Differences between rocks and minerals:

The differences between rocks and minerals are as follows-

Read And Learn Also WBBSE Solutions For Class 7 Geography

Question 2. What is meant by a rock? Describe the various types of rocks.
Answer:

Rock:

A rock can be defined as a naturally formed solid aggregate of one on more minerals present in varying proportions. In other words, all components that make up the Earth’s solid crust are called rocks.

Classification of rocks:

Based on origin, rocks can be classified into three types. They are as follows-

1. Igneous rock:

• Igneous rock is formed by the cooling and solidification of hot molten lava or magma that comes out on the Earth’s surface or remains within the Earth’s interior due to volcanic activity.
• Igneous rocks are the first-formed rocks on the Earth’s surface and are also known as primary rocks.

Example: Granite and basalt.

2. Sedimentary rock:

• Sedimentary rocks are formed when igneous rocks get weathered and eroded by different natural agents (such as rivers, wind, glaciers, and ocean waves).
• Erosion leads to the formation of small pebbles, cobbles and sand particles.
• These smaller rock fragments are then transported by natural agents like rivers and wind are then deposited in layers under the sea as well as in other locations.
• These layers of sediments under the sea get hardened and compacted over time to form hard rocks called sedimentary rocks.

Examples: Sandstone, mudstone, limestone.

3. Metamorphic rock:

• Metamorphic rocks are formed when pre-existing igneous and ‘sedimentary rocks change into hard, crystalline rocks due to the effects of temperature and pressure of overlying materials.
• This process is known as metamorphism.

Example: Marble from limestone and phyllite from slate.

Question 3. Make a comparative study of igneous, sedimentary and metamorphic rocks.
Answer:

A comparative study of igneous, sedimentary and metamorphic rocks:

A comparative study of igneous, sedimentary and metamorphic rock is tabulated below-

 

Question 4. Explain the importance of rocks in human life.
Answer:

Importance of rocks in human life:

The importance of rocks in the life of man can be classified into two groups-

1. Direct importance:

1. Fossil fuels like coal and petroleum are obtained from the layers of sedimentary rocks.
2. Valuable minerals like gold, silver, and copper are found in igneous rocks.
3. Granite, basalt, etc. are used in the construction of roads.
4. Limestone is used in cement and steel industries.
5. Sandstone or claystone is used in the construction of buildings.

2. Indirect importance:

1. Weathering of rocks like granite, gneiss, etc. forms red soil.
2. Weathering of rocks like basalt forms black soil or regur.
3. The permeable or impermeable nature of rocks determines its water-holding capacity.

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Question 5. What are igneous rocks?
Answer:

Igneous rocks :

• Igneous rocks are formed through the cooling and solidification of hot molten lava or magma that comes out on the Earth’s surface or remains beneath it due to volcanic activity.
• The term ‘igneous’ comes from the Latin word ‘ignis’ meaning fire.
• For example, the two most important igneous rocks are granite and basalt.
• Igneous rocks are the first formed rocks on the Earth’s surface and are also known as primary rocks.

 

 

Question 6. What are sedimentary rocks?

Answer:

Sedimentary rocks:

• Igneous rocks get disintegrated into small pebbles, cobbles and sand particles by the action of different natural agents such as rain, running water, wind, glacier, etc.
• These fragments of rocks and sediments are then transported by glaciers, rivers, streams, winds, etc. and are subsequently deposited in layers under the sea.
• With time, after being subjected to high temperatures and great pressure, these layers of sediments get hardened and compacted to form sedimentary rocks, such as sandstone, mudstone, and limestone.
• Sedimentary rocks are formed by the deposition of sediment layers over a long period of time and so fossils or impressions of dead organisms are found in these rocks.

Examples of sedimentary rocks are sandstone, claystone, and limestone.

 

Question 7. What are the characteristics of sedimentary rocks?
Answer:

The characteristics of sedimentary rocks are as follows-

1. Sedimentary rocks are formed in strata or layers. So they are also called stratified rocks.
2. As they are soft and light, sedimentary rocks are prone to erosional activities.
3. Sedimentary rocks are porous.
4. Fossils are found in this type of rock.
5. Fossil fuels such as mineral oil, coal, and natural gas are found in sedimentary rocks.

 

 

Question 8. What are the uses of sedimentary rocks?
Answer:

The uses of sedimentary rocks are-

1. Fuels like coal, mineral oil and natural gas are found in sedimentary rocks.
2. Sedimentary rocks like limestone and dolomite are used in the iron and steel industry, the cement industry and the construction of houses.
3. Mudstone is used in idol-making.
4. Sedimentary rocks being porous, act as an important source of groundwater.

Question 9. What are metamorphic rocks?
Answer:

Metamorphic rocks:

• The word ‘metamorphism’ comes from the Greek word ‘meta’ meaning ‘change’. Under high temperatures and pressure of overlying materials, a pre-existing igneous or sedimentary rock may change into a hard new rock which is called metamorphic rock.
• Their original character and appearance get altered due to various processes-thus changing their intrinsic properties like colour and hardness.
• Sometimes, a metamorphic rock may change into a completely new form with a new mineral composition, such as, gneiss from granite (igneous rock), marble from limestone (sedimentary rock), phyllite from slate (metamorphic rock), etc.

 

 

Question 10. Write the different characteristics of metamorphic rocks.
Answer:

The different characteristics of metamorphic rocks are as follows-

1. Metamorphic rocks being hard and heavy are resistant to erosion.
2. Metamorphic rocks are non-stratified.
3. The fossils present in sedimentary rocks get destroyed due to heat and pressure. So, fossils are absent in metamorphic rocks.
4. Metamorphic rocks are the last to form on the Earth’s surface.

Question 11. What are the uses of metamorphic rocks?
Answer:

The uses of metamorphic rocks are-

1. Valuable minerals like iron, copper, gold, silver, mica, and manganese, are found in metamorphic rocks.
2. As metamorphic. rocks erode slowly, they can be used for a variety of purposes. For example-Slate is used for writing. It is also used for making floors and roofs of houses.
3. Marble, which is a metamorphic rock, is used for making palaces, monuments, houses, temples, etc.
4. Gneiss is used in the construction of bridges and dams.

Question 12. Write a brief note on the Rock cycle.
Answer:

Rock cycle:

• Magma solidifies to form igneous rocks which get disintegrated and decomposed by physical and chemical weathering.
• These materials are then transported by various external agents such as rivers, glaciers and winds and are deposited in layers on the land surface or sea floor forming sedimentary rocks.
• These in turn, gets metamorphosed when subjected to high temperature and pressure, forming metamorphic rocks.

 

 

Similarly, igneous rocks may transform into metamorphic rocks, metamorphic and sedimentary rocks into igneous rocks and metamorphic rocks into sedimentary rocks. This transformation of one rock to another over time is called the Rock cycle.

Question 13. What are fossils and how are they formed?
Answer:

Fossils:

Fossils are preserved remains or traces of plants, animals and other organisms from the remote past. The geological age of rocks may be determined with the help of fossils.

 

 

Formation of fossils:

• As living organisms die, its framework settles on the sea floor or land surface and is buried by sediments. With time, this sediment subjected to high pressure and temperature solidifies.
• The buried framework dissolves forming a mould. Water rich in minerals enter the mould and fill the cavity, leaving behind a cast, similar to the original framework, known as a fossil.

Example:

Fossils or impressions of plants and animals are found in the layers of sedimentary rocks in the Himalayan region.

Question 14. Why are fossils are found in sedimentary rocks?
Answer:

Fossils are found in sedimentary rocks:

• The process of formation of sedimentary rocks is highly responsible for the presence of fossils in its layers.
• When layers of sediments accumulated on the sea floor or land surface are subjected to high temperature and pressure, the plant and animal remains buried within dissolve or undergo cementation and solidification leaving behind casts or traces.
• This is the reason fossils are found in sedimentary rocks. For example, numerous fossils have been found in the Himalayas as it is formed of sedimentary rocks.

Question 15. What is the economic importance of rocks?
Answer:

1. Direct importance:

1. Fossil fuels like coal and petroleum are obtained from the layers of sedimentary rocks.
2. Valuable minerals like gold, silver, and copper are found in igneous rocks.
3. Granite, basalt, etc. are used in the construction of roads.
4. Limestone is used in the cement and steel industries.
5. Sandstone or claystone is used in the construction of buildings.

Question 16. Write a brief note on gneiss.
Answer:

Gneiss:

Gneiss is a type of metamorphic rock formed due to the metamorphism of granite.

• The rock particles are quite large in size and minerals are present in clear bands.
• It is pink in colour. The mineral constituents of gneiss are quartz, mica, and feldspar.

 

 

WBBSE Chapter 6 Rock And Soil Topic A Rock Short Question And Answers

Question 1. What type of rocks are the sharp-edged stones found on a railway track?
Answer:

The sharp-edged stones found on a railway track:

• The sharp-edged, dark grey stones found on railway tracks are actually basalt rock. Basalt is an igneous rock. So, when basaltic rocks are cut by machines, they generally attain sharp edges.
• These stones are used to bear the load of the railway lines, keep the railway lines in place, help in drainage and prevent the growth of weeds on the railway tracks.

Question 2. What is a mineral?
Answer:

Mineral:

A mineral is a naturally-occurring inorganic substance that consists of one or more elements to form a rock.

Question 3. What is a rock?
Answer:

Rock:

• All components that make up the Earth’s solid crust are called rocks. A rock may be defined as a naturally formed solid aggregate of one or more minerals present in varying proportions.
• The term ‘rock’ not only refers to hard materials like granite but also includes loose and smaller particles like sand, pebbles, etc.

Question 4. Rocks are actually naturally formed aggregates of one or more minerals. Can you name some minerals which are commonly used in our daily life?
Answer:

Rocks are actually naturally formed aggregates of one or more minerals.

Some minerals which are commonly used in our daily life are salt, rock salt, baking soda, alum and pencil lead.

Question 5. How do rocks form on the Earth’s surface?
Answer:

Rocks form on the Earth’s surface:

• The first rock to originate on the Earth’s surface is igneous rock, also known as primary rock. Magma comes out on the Earth’s surface through volcanic vents or fissures.
• It cools and solidifies to form igneous rock.
• Sedimentary rocks form from igneous rocks whereas metamorphic rocks originate from both igneous and sedimentary rocks.

Question 6. How can you classify rocks?
Answer:

Classification Of rocks:

All components that make up the Earth’s solid crust are called rocks.

According to the origin, rocks can be classified into three types-

1. Igneous rocks,
2. Sedimentary rocks and
3. Metamorphic Rocks.

Question 7. Why are metallic minerals commonly found in igneous rocks?
Answer:

Metallic minerals commonly found in igneous rocks:

• Valuable minerals like gold, silver, iron, copper etc. are found in the magma of the Earth’s interior.
• Since igneous rocks are formed from this magma, they are rich in metallic minerals.

Question 8. Write a short note on granite.
Answer:

Granite:

• Granite is an igneous rock formed deep inside the Earth. Hot, molten magma from the Earth’s interior cools and solidifies over time to form granite.
• Since it is formed in the deep interior of the Earth, it is also called plutonic rock.
• In the absence of air, rate of cooling is very slow in the Earth’s interior, thus forming large crystals
•  Granite can be red, pink or white in colour. The mineral constituents of granite are quartz, feldspar and mica.

Question 9. Briefly write about the rock basalt.
Answer:

Rock basalt:

• Basalt is a type of igneous rock. Hot, molten, magma that comes out of the Earth’s interior through volcanoes cools rapidly and solidifies very fast to form fine crystals of basalt.
• Basalt is black in colour and is very hard. The mineral constituents of basalt are pyroxene, iron, and olivine.

Question 10. Write a brief note on sandstone.
Answer:

Sandstone:

• Sandstone is a type of sedimentary rock. Compaction and hardening of sand particles lead to the formation of this rock which can be found in several colours like white, brown, red, etc.
• Sand particles are of various shapes.
• If the sandstone is formed of fine particles, then it is called siltstone while a sandstone made of large particles is called a conglomerate.

Question 11. What do you know about limestone?
Answer:

Limestone:

Limestone is a sedimentary rock made of marine organisms.

• Chemical reaction brings about the cementation of calcium carbonate (CaCO₃) to form limestone.
• Deposits of decomposed shells and skeletons of marine organisms form this sedimentary rock.
• The limestone is brownish in colour. It is composed of calcite, which is very soft by nature.

Question 12. Write a short note on the slate.
Answer:

Slate:

• Slate is a type of metamorphic rock. Great pressure metamorphoses mudstone, which is a sedimentary rock into slate. Its particles are very fine and smooth.
• Slate is usually found in the form of smooth, flat sheets and is used to make roofs of houses. Slate is generally bluish-black in colour.

Question 13. Briefly mention the origin of different rocks.
Answer:

The origin of rocks are given in the following table-

 

Question 14. What are the characteristics of sedimentary and igneous rock according to strength?
Answer:

The characteristics of sedimentary and igneous rock according to strength are as below-

Question 15. What are stratified rocks?
Answer:

Stratified rocks:

• Rocks which have different layers or strata are called stratified rocks.
• Since sedimentary rocks have strata, they are also known as stratified rocks.

Question 16. What are unstratified rocks?
Answer:

Unstratified rocks:

• Unstratified rocks are those which do not have any strata or layers in them.
• Igneous rocks and metamorphic rocks are called unstratified rocks because no strata or layers are found in these rocks.

Question 17. Describe the origin of igneous rocks.
Answer:

The origin of igneous rocks:

• In the beginning, when the Earth was formed, it was just a glowing ball of gas. Gradually, it cooled down and its molten, volatile surface solidified.
• Then in later geologic periods, hot molten materials came out through volcanic openings or cracks and faults, cooled and then solidified to form igneous rocks.
• Since igneous rocks are the first formed rocks on the surface, they are also known as primary rocks.

Question 18. What are the uses of igneous rocks?
Answer:

The uses of igneous rocks are-

1. Igneous rocks are very hard and are thus, used in the construction of buildings and roads.
2. Metallic minerals (For example, iron, copper, silver, gold, etc) are found in igneous rocks.
3. Regur soil is formed by weathering of basalt and is very useful for agriculture.
4. Ancient temples and monuments in India were constructed with granite such as, in certain temples at Rameswaram and Tiruchirapalli of south India.

Question 19. What are the characteristics of igneous rocks?
Answer:

The characteristics of igneous rocks are-

1. Igneous rocks are compact and massive.
2. Igneous rocks do not have layers or strata and are also called unstratified rocks.
3. They may possess metallic minerals.
4. These rocks are hard and so they do not erode easily.
5. They do not contain fossils.
6. These rocks are non-porous as water cannot percolate.
7. Igneous rocks are also called primary rocks.
8. On polishing, these rocks appear smooth and glossy.

Question 20. Why are fossils not found in igneous rocks?

Answer:

Fossils are not found in igneous rocks because of the following reasons-

1. Igneous rocks were formed at such a time when living organisms did not exist on Earth.
2. If any organism or organic matter would have existed, then it would have got crushed under the heat, leaving behind no impressions during the cooling and solidification of magma to form igneous rocks.

WBBSE Chapter 6 Rock And Soil Topic A Rock Very Short Question And Answers

Question 1. What is actually a naturally formed aggregate of one or more minerals and is also an integral part of the lithosphere?
Answer: Rock.

Question 2. What is that naturally-occurring inorganic substance that consists of one or more elements to form a rock?
Answer: Mineral.

Question 3. Which rock, formed from cooled molten lava, was the first to be formed on the surface of the Earth?
Answer: Primary or Igneous rock.

Question 4. Which type of rock do we see right next to railway tracks?
Answer: Basalt.

Question 5. Which rocks do not have strata or layers?
Answer: Non-stratified rocks.

Question 6. What is another name for igneous rock?
Answer: Primary rock.

Question 7. What do we call the magma that reaches the Earth’s surface through a volcanic vent or fissure?
Answer: Lava.

Question 8. What is the term used to measure the void spaces in a rock structure?
Answer: Porosity.

Question 9. Name an igneous rock that is commonly used to construct roads.
Answer: Basalt.

Question 10. Which type of rock is formed by the solidification of lava?
Answer: Extrusive igneous rock.

Question 11. Which type of rock is formed by the solidification of magma?
Answer: Intrusive igneous rock.

Question 12. Which factors are responsible for the transformation of igneous and sedimentary rocks into metamorphic rocks?
Answer: Great heat and pressure of overlying materials.

Question 13. Which type of rocks are soft and brittle?
Answer: Sedimentary rocks.

Question 14. Which rocks have strata or layers?
Answer: Stratified rocks or sedimentary rocks.

Question 15. Which rock is formed due to the deposition of silt and sediment carried down by rivers on their banks?
Answer: Sedimentary rock.

Question 16. Name the black rock on which we can write with chalk.
Answer: Slate.

Question 17. Which rock is used as a raw material in the cement industry?
Answer: Limestone.

Question 18. Which rock is formed when the pre-existing igneous and sedimentary rocks are subjected to very high temperatures and pressure?
Answer: Metamorphic rock.

Question 19. During the formation of which rock do the minerals arrange themselves in one direction making the extraction of minerals easy?
Answer: Metamorphic rock.

Question 20. Name a metamorphic rock that is commonly used to construct monuments.
Answer: Marble.

Question 21. What do we call the remains and impressions of plants and animals embedded in sedimentary rocks formed due to pressure from the overlying sediment layers?
Answer: Fossils.

Question 22. Which fossil fuel, found in sedimentary rock, has hydrocarbon as its main constituent?
Answer: Mineral oil or petroleum.

Question 23. Which black-coloured rock-used as fossil fuel-is formed from plant remains that have been pressurised for millions of years?
Answer: Coal.

Question 24. What is the process of transformation of rock from one form to the other known as?
Answer: Rock cycle.

Question 25. In which type of rock is a fossil fuel found?
Answer: Sedimentary rock.

Question 26. Which rock is formed due to the deposition of sediments in layers within the waterbodies?
Answer: Sedimentary rock.

WBBSE Chapter 6 Rock And Soil Topic A Rock Fill In The Blanks

Question 1. Most of the Earth’s crust is composed of _________ minerals.
Answer: Silicate

Question 2. _________ is used in the construction of roads.
Answer: Basalt

Question 3. The Earth’s crust is composed of naturally- occurring substances called _________.
Answer: Rocks

Question 4. According to the origin, rocks can be classified into _________ types.
Answer: Three

Question 5. All rocks have their origin from _________ rocks.
Answer: Igneous

Question 6. Basalt is an example of _________ rock.
Answer: Igneous

Question 7. Granite is an example of _________ rock.
Answer: Igneous

Question 8. The western plateau of West Bengal is composed of _________ and _________.
Answer: Granite and gneiss

Question 9. The thin, outermost layer of the Earth on which we live is called _________.
Answer: Lithosphere

Question 10. Igneous rocks on the Earth’s surface have been weathered, _________ and broken into rock debris to form sand, pebbles and gravel.
Answer: Eroded

Question 11. An example of porous rock is _________.
Answer: Sandstone

Question 12. Chalk is an example of _________ rock.
Answer: Sedimentary

Question 13. Gneiss is an example of _________ rock.
Answer: Metamorphic

Question 14. The process by which rocks crumble and decay is known as _________.
Answer: Weathering

Question 15. Impressions of plants and animals embedded on sedimentary rocks are called _________.
Answer: Fossils

Question 16. Limestone Sedimentary rock:: Marble: _________.
Answer: Metamorphic rock

Question 17. Igneous rock: Basalt:: Mudstone: _________
Answer: Sedimentary rock

WBBSE Chapter 6 Rock And Soil Topic A Rock True Or False

Question 1. Sedimentary rocks are formed from sediment particles.
Answer: True

Question 2. Metamorphic rocks are formed under the influence of high temperature and pressure in the Earth’s interior.
Answer: True

Question 3. The first rock formed on the surface of the Earth is igneous rock.
Answer: True

Question 4. Metamorphic rocks are also known as stratified rocks.
Answer: False

Question 5 Minerals are not found within rocks.
Answer: False

Question 6. Fossils are found in sedimentary rocks.
Answer: True

Question 7. Strata cannot be found in igneous rocks.
Answer: False

Question 8. Sedimentary rocks are also called stratified rocks.
Answer: True

Question 9. Deccan Trap is made up of basalt.
Answer: True

Question 10. Porosity is an important characteristic of sedimentary rocks.
Answer: True

Question 11. Coal is an example of igneous rock.
Answer: False

Question 12. Sandstone is an example of stratified rock.
Answer: True

Question 13. Fossil fuels like coal and petroleum are found in igneous rocks.
Answer: False

Question 14. The metamorphosed form of limestone is marble.
Answer: True

Question 15. Cooling and solidifying of magma in the Earth’s interior forms intrusive igneous rocks.
Answer: True

Question 16. Minerals are organic components.
Answer: False

Question 17. Augite is an example of a rock-forming mineral.
Answer: True

Question 18. Limestone is used in the pottery industry.
Answer: False

WBBSE Chapter 6 Rock And Soil Topic A Rock Match The Columns

Question 1.

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