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
→ 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.
- 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.
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.
- 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.
- 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.
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.