RBSE Class 11 Geography Notes Chapter 6 Rocks

Go through these RBSE Class 11 Geography Notes Chapter 6 Rocks contain important concepts so that students can score better marks in the exam.

Rajasthan Board RBSE Class 11 Geography Notes Chapter 6 Rocks

→ The upper layer of the earth (earth’s crust) is formed from the composition of various
minerals.

→ The word ‘rock’ is used for any hard object.

→ According to geological perspective, all the substances that have formed the earth’s crust, whether they are hard or soft, are called rocks.

Types of Rocks

  • There are 3 types of rocks – Igneous Rocks, Sedimentary Rocks and Metamorphic Rocks.
  • The nature of the crust is hard or soft according to the nature of the rocks which form it.

Igneous Rocks

  • Rocks made of hot and fluid magma and lava are called igneous rocks.
  • Being the first to be formed, these are called the primary rocks.
  • About 95 percent part of the igneous rocks extends to the thickness of up to 16 km. in the upper part of the crust.
  • The features like lack of layers, lack of fossils, lack of porosity, crystallized form, hardness, and abundance of metallic minerals are found in these rocks.

RBSE Class 11 Geography Notes Chapter 6 Rocks

Classification of Igneous Rocks

  • On the basis of the place of formation, the igneous rocks are classified into two parts – Intrusive and Extrusive Rocks.
  • Intrusive igneous rocks are further classified into Plutonic and Hypabyssal Rocks.
  • Granite is Plutonic; Phacolith, Lacolith, Lapolith and Dykes are Hypabyssal; Gabbro and Basalt are Extrusive Igneous Rocks.
  • On the basis of chemical composition, the igneous rocks are classified into Acidic, Basic, Intermediate and Ultra-Basic Rocks.

Sedimentary Rocks

  • These rocks are formed by the solidification of the layers of sediments through the processes of weathering and erosion.
  • These rocks are found on almost 75% part of the total earth’s surface.
  • Sedimentary rocks contain several layers, strata, are porous contain fossils and are soft.

Classification of Sedimentary Rocks

  • Sedimentary rocks are classified on the basis of the resources and the sediments used in their formation.
  • On the basis of the sediments used, these rocks are classified into clastic rocks, compared of fragments or clasts, of pre-existing minerals and rocks. A clast is a fragment of gealogical detritus, chunks; Organically Formed Rocks and Chemically Formed Rocks.
  • On the basis of the resources used in the formation, these rocks are classified into Aqueous Rocks, Aeolian Rocks and Glacial Rocks.

Metamorphic Rocks

  • Rocks made by basic changes in the properties and structure of the original rocks without their disintegration and dissociation are called metamorphic rocks.
  • For the metamorphism of metamorphic rocks, water, heat and pressure play an important role.
  • These rocks are harder than the original rocks and have an abundance of metallic minerals.

RBSE Class 11 Geography Notes Chapter 6 Rocks

Metamorphism of Rocks

  • Metamorphism of rocks is divided into Thermal Metamorphism, Regional or dynamic Metamorphism, Hydro Metamorphism and Thermo-Hydro Metamorphism.
  • In the metamorphism of the igneous rocks, granite metamorphosed into gneiss, basalt into amphibolite and gabbro into serpentine.
  • In the metamorphism of the sedimentary rocks, sandstone metamorphosed into quartzite, limestone into marble, shale into slate and coal metamorphosed into graphite and diamond.
  • Re-metamorphism of some metamorphic rocks, like slate metamorphosed into schist and schist re-metamorphosed into phyllite.

Rocks Notes Important Terms

→ Igneous Rocks: The word igneous is originated from the Latin word ignis, the meaning of which is fire.

→ Sedimentary Rocks: The disintegration, dissociation and transport of rock-powders of the existing rocks takes place through the various means of weathering and erosion. The rocks formed as a result of accumulation of the sediments at a place are called sedimentary rocks. Due to their layered structure, they are also known as the Layered Rocks.

→ Metamorphic Rocks: The meaning of metamorphic is – change in the form. Due to the changes in the forms of the igneous and sedimentary rocks by the action of heat and pressure, the metamorphic rocks are formed.

→ Fossil: The remains or impression of a prehistoric plant Ot animal embedded in rock and preserved in petrified form.

→ Weathering: The process by which rocks are broken down into small grains and soil.

→ Chemical Weathering: A process of weathering under which dissociation begins as a result of chemical changes in the rocks by which erosion of the rocks takes place.

→ Physical Weathering: The process of disintegration in the rocks by physical factors like sun’s heat, light, wind, water, etc.

→ Metallic Minerals: The minerals from which metals are obtained are called metallic minerals, like – iron ore, copper ore, manganese ore, etc.

→ Plutonic Rocks: The rocks formed when the lava is cooled down and solidified beneath the earth’s surface are called plutonic rocks.

→ Phacolith: The lava solidified in the syncline of folded mountains at the time of volcanic eruption.

→ Lacolith: A large mass of igneous rocks formed beneath the earth’s surface, whose lower part is generally flat and upper part is in the shape of a dome.

→ Lapolith: Lapolith is a word of the German language, whose meaning is a shallow basin.

→ Dykes: When the lava deposits in the cracks are almost at the right angle of the earth’s surface, then a wall-like structure formed is formed.

→ Sills: When the lava flows, sills is a group of igneous rocks formed in the shape of layer.

→ Batholith: When a large body of magma gets cooled down at more depth in the earth’s crust, then it develops into the shape of a dome.

→ Acidic Rock: Rocks formed of high content silica lava. The amount of silica is more than 65% in these rocks.

→ Basic Rock: The amount of silica is in between 45% to 55% in these rocks.

→ Ultra-Basic Rock: Rocks in which the amount of silica is less than 45% are called Ultra-Basic Rocks.

→ Denudation: The combined processes of weathering, erosion, transportation and deposition of the rocks is called denudation.

→ Vegetation: All plant life of a region. This includes all plant species like algae, grass, shrubs, trees, etc.

→ Rocks-Flour Formed Rocks: Rocks formed of the fine solid matter originated by the abrasion of any glacier bottom.

→ Loess: The deposits of the very fine particles of soil and dust particles blown away by the winds.

→ Organic Rock: Rocks in which the debris of living-organisms and vegetation is found in abundance.

→ Aqueous Rock: Rocks which are formed by the deposition of sediments in aquatic parts are called Aqueous Rocks.

→ Aeolian Rock: The accumulation of materials caused by air or related to it, is called Aeolian rock.

→ Glacial Rocks: Rocks which are formed by the transportation and deposition of pebbles and boulders by the glaciers.

→ Metamorphic Rock: Rocks which are formed by the changes in the forms of igneous and sedimentary rocks due to the action of heat and pressure.

→ Thermal Metamorphism: The process of change in the form of the igneous and sedimentary rocks and rebuilding of granules in their structure by the effect of extreme heat.

→ Hydro Metamorphism: The process of change in the rock-minerals in the form of a solution by the mixing of chemical materials with water.

→ Thermo-Hydro Metamorphism: Metamorphism of rocks occurred due to the spread of hot water over the top of the rocks.

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