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NCERT Solutions for Class 8 Science - Rocks and Minerals

Q1: Name the three layers of the earth.
Ans: The three layers of the earth are:

  1. Crust: It is the outermost solid part of the earth. It is brittle in nature. 
  2. Mantle: The portion of the interior beyond the crust is called the mantle. 
  3. Core Outer core, Inner core: The core-mantle boundary is located at the depth of 2,900 km.  The outer core is in a liquid state while the inner core is in solid state.
    NCERT Solutions for Class 8 Science - Rocks and Minerals

Q2: Name the three types of rocks with one example each.
Ans: The three types of rocks are:

  1. Igneous rock: Igneous rocks solidify from molten rock. Example: Pumice
  2. Sedimentary rock: Sedimentary rocks are layered. Example: Shale
  3. Metamorphic rock: Metamorphic rocks form when sedimentary, igneous, or pre-existing metamorphic rocks are changed by environmental factors. Example: Marble
    NCERT Solutions for Class 8 Science - Rocks and Minerals

Q3: What are metamorphic rocks? How are they formed?
Ans: Rocks that have changed their form over time are called metamorphic rocks. They are formed due to physical and chemical changes in igneous, sedimentary, or older metamorphic rocks themselves due to heat and pressure.

Q4: What are minerals? Give any three examples of minerals.
Ans: All rocks are made up of substances called minerals. Minerals are chemical substances that occur in nature. Eg: gold, silver and iron.

Q5: What are magnets? Mention the two types of magnets with examples.
Ans: Magnets are substances that can attract objects made up of iron, cobalt and nickel. There are two types of magnets:-

  1. Natural magnets: These are found in nature and these are made up of a mineral called magnetite.
  2. Man-made: These are made by man from iron, cobalt and nickel.
    NCERT Solutions for Class 8 Science - Rocks and Minerals

Q6: Name the different types of igneous rocks. Describe any two.

Ans: The different types of igneous rocks are:

  1. Granite
  2. Obsidian
  3. Pumice

Obsidian:

  • It is smooth and glassy and is formed by quick cooling of lava.
  • It is used in making jewellery and ornaments.
  • It is usually black or dark coloured.

Pumice:

  • It is porous, or full of holes is formed from lava that is frothy with a lot of air within it.
  • It is the only rock that can float.
  • It is used in making light weight materials like concrete blocks.

Q7: How are sedimentary rocks formed? Name the different types of sedimentary rocks. Describe any one.
Ans: Sedimentary rocks are formed by repeated deposition of rock particles that are worn away from mountains by winds and water.
The different types of sedimentary rocks are:

  1. Conglomerate
  2. Sandstone
  3. Shale
  4. Limestone

Shale:

  1. It is made up of solidified clay apart in thin layers.
  2. It is used in making bricks and cement.
    NCERT Solutions for Class 8 Science - Rocks and Minerals

Q8: What are the different types of metamorphic rocks? Describe any two.
Ans: The different types of metamorphic rocks are:

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

Slate:

  1. It is formed from shale a sedimentary rock.
  2. Like shale, it splits into flat layers.
  3. It is used in making brick and cement.

Gneiss:

  1. It is formed from granite.
  2. It has different kinds of minerals in it< giving it a striped or streaked look.
  3. It is used as building stone.

Q9: Describe the various uses of rocks and minerals.
Ans: 
Uses of rocks are:

  1. Rocks are used as building material for making schools, houses, roads and bridges. Some rocks are used in their original form while some are used to make bricks, cement, tar and concrete. For eg: granite, limestone, sandstone and marble.
  2. Rocks give us useful metals for eg meals like iron, copper and aluminium are used for making utensils and precious metals like gold, platinum are used for making jewellery.
  3. Rocks give us fuel for eg: coal is used for producing electricity, heating and moving nuclear energy.
  4. Rocks are used as gemstones for eg: diamond, ruby, sapphire and emerald are used for making jewellery because when they are polished they appear shiny and beautiful.

Uses of minerals:

  1. Minerals like Sulphates and Nitrates are used as fertilizers because they help the plant to grow.
  2. Minerals are a very important part of our diet. For eg: minerals like calcium, sodium and iron are required for the healthy functioning of our body.

Q10: Continuous heating and cooling breaks even a hard rock into small pieces of sand. What should we learn from this process?
Ans: Continuous heating and cooling can break a hard rock into tiny pieces like sand. This teaches us that small changes over time can have big effects. Just like rocks, being patient and adaptable helps us handle challenges in life.

Q11: How does heat and pressure of earth contribute to the formation of metamorphic rocks?
Ans: Heat and pressure of the earth can change the physical or chemical composition of igneous or sedimentary rocks and leads to the formation of metamorphic rocks.

Q12: Can we find fossils in the granite or marble mines? Why?
Ans: We can find fossils in the granite or marble mines because it is formed from sedimentary rocks which can have fossils in them during their formation.

Q13: What is the difference between magma and lava.
Ans: The difference between magma and lava is:

  1. Magma: Molten rock inside the earth is called magma.
  2. Lava: Molten magma that flows out onto the surface of the earth is called lava.

Q14: Name the important minerals that are found in igneous rocks.
Ans: The important minerals that are found in igneous rocks are:

  1. Mica
  2. Feldspar
  3. Magnesium
The document NCERT Solutions for Class 8 Science - Rocks and Minerals is a part of the Class 5 Course Science Class 5.
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FAQs on NCERT Solutions for Class 8 Science - Rocks and Minerals

1. What are the differences between rocks and minerals?
Ans. Rocks are made up of one or more minerals, while minerals are naturally occurring inorganic substances with a specific chemical composition and atomic structure.
2. How are rocks classified?
Ans. Rocks are classified into three main types based on how they are formed: igneous rocks, sedimentary rocks, and metamorphic rocks.
3. What is the rock cycle?
Ans. The rock cycle is a continuous process where rocks are formed, broken down, and reformed over time through processes such as weathering, erosion, melting, and cooling.
4. How can you identify minerals?
Ans. Minerals can be identified based on their physical properties such as color, luster, hardness, cleavage, and crystal form. Special tests like streak, acid reaction, and magnetism can also help in identification.
5. Why are rocks and minerals important?
Ans. Rocks and minerals are important for various reasons such as providing natural resources like metals and building materials, contributing to geological processes, and serving as valuable tools for understanding Earth's history and structure.
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