As we know that the rocks are changing or transformed with time due to the action of atmospheric agencies (including temperature, pressure, water, wind, etc.) The cyclic process through which, rocks are transformed from one category to another one such process is called the Rock cycle.
In the Rock cycle process, the igneous rocks are the first state rocks, which are formed directly from the magma by cooling and recrystallization of magma, and hence these types of rocks are also known as primary rocks.
During weathering and erosion process, the igneous rocks are broken down into smaller rock fragments, which are known as sediments. These sediments are transported by the winds, water, etc., and deposited in deltas, riverbanks, the bottom of the waterfall, etc. here sediments are accumulated through the sedimentation process, and then the loose and soft sediments are converted into hard rocks through lithification and diagenesis process.
Due to the influence of high temperature and pressure, the composition, texture, the structure of the sedimentary rocks changes and forms a new type of rock, known as metamorphic rocks.
When the temperature and pressure gradually increase, the metamorphic rocks are started to melt and converted into magma from which, igneous rocks are formed again. Sometimes, the metamorphic rocks are broken down due to the atmospheric agents acting on them or collision occurs between them, which converted them into sediments and sedimentary rocks are formed from it. In this way, the rock cycle process is rotating.
The lithosphere is consisting of these kinds of rocks, in which the number of igneous rocks is greater than the metamorphic and sedimentary rocks. The atmospheric agencies like temperature, pressure, wind, water, etc) play an important role in the case of formation of three types of rocks by causing weathering and erosion.
The action of atmospheric agencies like wind, sun, frost, water, plant, and organism breaks a huge piece of rocks into smaller pieces and from the soil. This phenomenon is called weathering. there are three types of weathering-
1) Physical weathering:
a) In physical weathering, a rock breaks into smaller pieces from bigger pieces without any chemical change.
b) The physical weathering increases the surface area for the chemical attacks.
c) The principal agents of physical weathering are: 1) frost, 2) heating and cooling, and 3) organism
Example of physical weathering:
· 1) Freezing water or frost wedging: When rain occurs, water enters the cracks, which are present in rocks. In winter this water freezes and converts to ice. Ice can expand about 9% of its volume and exerts great pressure on the walls of cracks. As a result, the rock breaks down into smaller pieces. This process is called “frost wedging”.
· 2) Salt weathering: when saltwater from the ocean or sea enters the cracks of rocks, the salts crystallize throughout the solution as water evaporates. As the salt crystals grow, they apply pressure on the walls of cracks. As a result, the rocks are broken down into smaller pieces. This process is known as salt weathering. This process occurs in a drier climate.
2) Chemical weathering:
a) In chemical weathering, rocks are broken down by the chemical decay of minerals.
b) In chemical weathering changes the original silicate minerals of igneous rock into new compounds.
c) During chemical weathering, a set of chemical reactions act on rocks which change their minerals to
More stable form.
d) Chemical weathering increases the volume of the new material.
e) The principal agencies of chemical weathering are- a) water, b) organism.
Examples of chemical weathering are-
Oxidation: The presence of dissolved oxygen in the water in contact with mineral surfaces leads to oxidation. Mafic minerals like pyroxene, amphiboles, and olivine contain some iron. When the oxygen comes in contact with an iron of this mineral, oxygen combines with iron to form iron oxide.
Limonite and hematite are the common products of oxidation that impart red and yellow colors to soils.
Hydration: In hydration, the water molecule combines chemically with minerals to produce new compounds. The formation of gypsum (CaSO4.2H2O) from dry anhydrate (CaSO4) is a good example of hydration. The Orthoclase feldspar, a mineral, is abundant in granite converted into Kaolin by hydration. Other hydrous silicates are formed from the primary silicates, such as pyroxene, olivine, amphibole, etc.
3) Biological weathering:
a) In biological weathering, the rocks are broken down chemically or physically
b) Physical examples are- plants roots, burrowing animals, etc.
c) chemical examples are – lichen, acid litter.
An example of biological weathering is-
1) Organism: soil formation is influenced by organisms (such as plants), micro-organisms (such as bacteria or fungi), burrowing insects, animals, and humans. Sometimes the root of plants enters the cracks of rock and grows in it. Due to scarcity of space inside the rock, breakdown the rock into smaller pieces and forms soil. Animals eat plants and their wastes dissolve into the soil slowly.
Erosion is a geological process through which earthen material (including soil, rock fragments, etc.) is worn away from one location on the Earth’s crust and transported to another location by natural forces such as wind or water.
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