Daily Class Notes - Geography - Rocks and Rock System PDF

1 DAILY CLASS NOTES Geography Lecture - 14 Rocks and Rock System  2 Rocks and Rock System  Lithosphere layer is also...

1 DAILY CLASS NOTES Geography Lecture - 14 Rocks and Rock System  2 Rocks and Rock System  Lithosphere layer is also called the Rockosphere because litho means rock.  Many elements of the earth get together to form compounds, these compounds are called minerals.  The aggregates of minerals and non-minerals are called rocks. These are formed due to heat, temperature, and pressure.  Rocks are the consolidated form of minerals of a wide variety, that are formed due to heat, temperature, and pressure.  These rocks form a major portion of the lithosphere.  Rocks are home to minerals and many minerals such as gold, silver, iron, calcium, platinum, copper, silica, silicates, nickel, etc. Important Minerals: Minerals Properties Silicates It has Quartz, Feldspar, and Ferromanganese. It is used in the glass industry. Sulphites It has Iron sulphide, Pirate (Iron ore). It has wide applications in the Iron and steel industries, infrastructure development, etc. Carbonates They are sensitive to or highly affected by weathering. Example: Calcite Metallic Elements It has Iron, Manganese, Aluminium, and Copper. It has wide applications in the automobile, aircraft, aluminum copper, refrigeration industries, etc.  3 Importance of Rocks:  Nature of Erosion: Erosion of soil depends upon the structure and composition of the rock. If the parent rock is hard then it will erode slowly erodes. If the parent rocks are soft rock then it will erode rapidly.  Type of Landscape: According to W.M. Davis the landscape of the land is decided by the dominant rocks in that region.  Dating age of the Earth: If the rocks are the book of history then the fossils are its pages. The study of the rocks gives information about the earth such as History, Geology, Life evolution, Environment, etc.  Constitute Manuscript of History of Earth: According to Morgan and Woolridge, the rocks give knowledge about the history of the earth. Classification of Rocks:  The study and analysis of rocks is called Petrology.  Classification of rocks is done on the basis of the formation of rocks.  Rocks are mainly divided into three types: 1. Igneous Rocks 2. Sedimentary Rocks 3. Metamorphic Rocks  4 Igneous Rocks:  These are formed due to cooling, solidification, and crystallization of magma or lava.  They are known as primary rocks because these were the first to originate during the crust formation of Earth. Subsequently, other rocks came such as sedimentary and metamorphic rocks were formed.  Also they are known as ‘Parent rocks’ and crystalline rocks.  Granite, gabbro, pegmatite, basalt, etc. are some examples of igneous rocks. Characteristics of Igneous Rocks:  These rocks are very hard and rough and do not allow water to percolate (diffuse inside). Igneous Rocks elements are strongly bonded together. But the Basalt type of igneous rocks can allow water percolation because it is soft rock.  Igneous rocks can be divided into Plutonic and Volcanic rocks, based on the place and time taken in cooling of molten matter.  These are granular and crystalline in nature and comprise different sizes and textures of grains. If the molten material of Magma is cooled suddenly at the surface, it results in small and smooth grains (small grains). Very slow cooling of magma results in the formation of big-size grains.  There are no layers in these rocks because these are formed due to cooling, which does not give layering ( crystallization only takes place).  Because of no percolation of water these rocks are least affected by weathering. There is no chemical reaction and weathering takes place. But if the grain size (coarse grains) is big it will be affected by the chemical weathering (Solution weathering, hydration, and oxidation) because there is a small space between the small grains of the big grains.  These rocks do not have any fossils. Because fossils got destroyed due to burning by hot magma. Classification of Igneous Rocks:  Igneous rocks classification on the basis of grain size:  5 1. Fine Grain: It is formed due to fast cooling. Example: Basalt. 2. Coarse Grain: It is formed due to slow cooling. Example: Granite.  Igneous rocks classification on the basis of silica content: 1. Acidic Rocks: It has more than 80% of silicon dioxide. 2. Basic Rocks: It has 45% to 65% of silicon dioxide. 3. Ultra Basic Rocks: It has less than 40% to 45% of silicon dioxide.  Igneous rocks classification on the basis of the cooling zone: Based on the place and time taken in cooling of the molten matter. 1. Plutonic Rocks: The cooling of Magma takes place below the crust at the depth, known as intrusive rocks. Intrusive igneous rocks cooled slowly at great depth within the crust or mantle are called Plutonic rocks. 2. Volcanic Rocks: The cooling of Lava takes place outside the crust, known as extrusive rocks. These rocks are dark and dense, seen in the USA (Snake Plateau, Columbia) and the Deccan region of India. Magma As Source Of Igneous Rocks:  The mixture of the molten Rocks, volatiles (gas), and other solids (originating from partial melting of the lower crust and upper mantle) is called Magma. It leads to the formation of the Igneous rocks.  When the molten magma goes down deep within the earth and gets solidified, it is called Plutonism. The molten magma can also come out on the surface of the earth through volcanic eruptions. Plutonic Rocks or Intrusive Rocks:  The molten matter which does not reach the surface and cools down very slowly at great depths.  6  This slow cooling will result in the formation of big-sized rocks (large grains).  Granite is the main example of intrusive rocks..  These rocks appear on the surface only after being uplifted and denuded. Lava or Volcanic Rocks or Extrusive rocks:  These are formed by rapid cooling of the lava erupted during volcanic activities.  Rapid cooling prevents crystallization, as a result, such rocks are fine- grained.  Basalt is a typical example of this type of rock.  The Deccan traps in the peninsular region have a basaltic origin. Plutonic Vs Volcanic Rocks Plutonic Volcanic rocks Intrusive rocks Extrusive rocks Granite Basalt Slow cooling allows big-sized crystals (large Rapid cooling prevents crystallization, as a result, such grains) rocks are fine-grained Less dense and are lighter in color than basic Denser and Darker in color rocks Acid Rocks:  These are characterized by a high content of silica of more than 80 percent, while the rest is divided among aluminum, alkalis, magnesium, iron oxide, lime, etc.  These rocks have a low percentage of heavy minerals like iron and magnesium and normally contain quartz and feldspar.  These rocks are hard, compact, robust, highly massive, and highly resistant to weathering.  These rocks constitute the SIAL portion of the crust of the earth.  Acidic magma cools fast and it does not flow and spread far away. Basic Rocks:  7  These rocks have low silica content (about 45% to 65%) and magnesia content is up to 40 percent. Other minerals like iron oxide, lime, aluminum, alkalis, potassium, etc. are also present in these rocks.  These rocks have low silica content and cool slowly. Thus it flows and spreads far away to form the source of the eruption.  The presence of heavy elements imparts a dark color to these rocks.  Basalt, gabbro, and dolerite are examples of these rocks.  These rocks are not very hard and weathered relatively easily. Acid Vs Basic Rocks: Acidic rocks Basic rocks High content of silica (up to 80 percent) and Poor silica content. Magnesia content (40 percent) Due to the excess of silicon, acidic magma Due to low silica content, the parent material of such cools fast rocks cools slowly High Volcanic mountains are formed of this Forms plateaus. Deccan Traps type of rock. Mt Fuji, Japan Lesser content of heavier minerals like iron Presence of heavy elements imparts a dark color to and magnesium and normally contain quartz these rocks. and feldspar. Hence they are lighter in color Granite, quartz, feldspar, etc. Basalt, gabbro, dolerite etc.. Add rocks are hard, compact, massive, and Not being very hard, these rocks are weathered resistant to weathering. relatively easily. Economic Importance of Igneous Rocks  The important minerals of great economic value found in igneous rocks such as magnetic iron, silicon, nickel, copper, lead, zinc, lead, chromite, manganese, gold, diamond, platinum, etc. These are utilized for infrastructure, manufacturing, electronics, jewelry, and medicines.  These rocks are used as building materials.  8  Silica is used in iron and steel plants, furnaces, cement industry, etc.  Granite is used as a building material as they come in beautiful shades.  When Magma cools down it becomes lava, It is the chief source of metal ores, many of which are associated with igneous rocks. 