Rocks: Their features and uses | Learning concepts
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Minerals and Rocks

Concept: Some Rocks and their Uses

We know that rocks can be broadly classified into—igneous rocks, sedimentary rocks and metamorphic rocks. Each of these categories includes different types of rocks. Let us have a detailed look at them.

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Igneous rocks:

1. Granite

Features Uses
  • Cooling of magma under the earth’s surface leads to the formation of granite.
  • It is hard rock with large grains.
  • The content of feldspar gives the rock its characteristic colour.
  • They vary from whitish-grey to pinkish-red depending on the mixture of minerals present in them.
  • Three main types of granite are—Quartz, Feldspar and Mica.
  • Making buildings and statues.
  • Used for flooring and making foundations of buildings.
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2. Pumice:

Features Uses
  • It is formed by the quick cooling of lava on the earth’s surface.
  • Pumice has a lot of air pockets in it. These have developed because of the gases trapped inside at the time of cooling.
  • It appears like a sponge.
  • It is light-weighted, and its colour varies from grey to cream.
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  • Used in powdered form for polishing teeth.
  • Used as a body scrubber.
  • Used for polishing furniture and floors.
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    3. Obsidian:

    Features Uses
  • It is also formed out of lava and looks like black glass.
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  • It has sharp edges and is hence used for making cutting tools.
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    4. Basalt:

    Features Uses
  • It is coarse-grained and has a glassy and compact appearance.
  • It is formed when the lava comes in contact with air, cooling down quickly.
  • Used for building pipes and wind turbine blades.
  • It is used in the textile industries.
  • This rock is crushed to make roads and pavements.
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    Sedimentary rocks:

    1. Sandstone:

    Features Uses
  • Sand particles harden together to form sandstone.
  • It is the most common sedimentary rock.
  • It mainly consists of quartz.
  • Its colour varies from yellow, brown to pink.
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  • It is used for constructing buildings. The famous Red Fort at Delhi is made of sandstone.
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    2. Shale:

    Features Uses
  • Clay and mud particles pile up together in layers to form shale.
  • Its texture is smooth.
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  • It is used for making tiles and bricks.
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    3. Conglomerate:

    Features Uses
  • Pebbles, when cement together with minerals, lead to the formation of conglomerate.
  • They have a rough texture.
  • Their colour varies from grey to orange.
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  • For building monuments, artefacts and sculptures.
  • Used in cement manufacturing industries.
  • In crushed form can be used for construction purposes.
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    4. Limestone:

    Features Uses
  • It majorly constitutes calcite, a mineral found in animal shells.
  • It varies from grey to white.
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  • It is used as a building material.
  • It is the major component of white cement.
  • It is used to synthesise lime, a chemical used to neutralise the acidity of the soil.
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    Metamorphic rocks:

    1. Marble:

    Features Uses
  • It is formed by the transformation of limestone, which is a sedimentary rock.
  • It is found in various colours and white is the most common.
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  • It is used for making statues and buildings.
  • The world-famous Tajmahal at Agra is made of marble.
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    2. Slate:

    Features Uses
  • It is formed by the metamorphosis of shale.
  • It is shiny and found in dark shades of grey and black.
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  • It is used for making roofs.
  • Blackboards are made of slates.
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    3. Gneiss:

    Features Uses
  • It is formed by the metamorphosis of granite.
  • It has visible dark and light bands.
  • It contains the shiny mineral mica that gives it its unique glittering appearance.
  • It is used for making floor tiles.
  • Cemetery monuments are crafted out of Gneiss.
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    4. Quartzite:

    Features Uses
  • It is formed by the metamorphosis of sandstone.
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  • It is used for making bricks and statues.
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    New Words:

    Cemetery: A place where dead people are buried

    Acidity: The amount of acid in a substance. Acid is a substance that tastes sour.

    Neutralise: To balance the effect of acidity.

    Did You Know?

    • Rocks are found in some things that we use at home like soaps, toothpaste and batteries.
    • The use of rocks started millions of years ago when the early men used them to make weapons and produce fire.
    • Diamond is the hardest substance known on earth and mainly comprises carbon.
    • Ruby and Sapphire used as precious gems are varieties of a mineral named Corundum.
    • The metamorphosis of Limestone forms a type of metamorphic rock called Granulite.

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