IAS Exam Preparation of Geography Section via Infographics
You will be tested by UPSC on Questions relating to Geomorphology. Rocks – Types, Characteristics and Related Processes is an important component of Geomorphology.
Geography for IAS Exam Preparation 2016
Topic – Types of Rocks and Related Processes
Types of Rocks
Rocks are broadly classified into 3 categories :
Igneous Rocks
- Igneous rocks are rocks which form from the cooling and solidification of magma. Thus they are the results of volcanic processes.
- Igneous rocks make up about 90% of the Earth’s crust. However, they are hidden from the surface by a thin layer of sedimentary and metamorphic rocks.
- They are crystalline and impervious. They are resistant to erosion and weathering
- The geological significance of Igneous rocks is that they come from the mantle. Hence, the minerals and chemistry of igneous rocks give information about the composition of the mantle.
- They host important mineral deposits such as uranium, tungsten, tin, chromium, platinum.
Igneous rocks can be of two types
Intrusive (plutonic) rocks
Intrusive igneous rocks are formed from magma that cools and solidifies within the crust
Extrusive (volcanic) rocks
Extrusive igneous rocks are formed at the surface, from magma released into the surface from volcanic eruptions
Mineral Composition of Igneous Rocks
| Felsic | Mafic | Ultramafic | |
| Intrusive | Granite | Gabbro | Peridotite |
| Extrusive | Rhyolite | Basalt | Komatite |
Did You Know?
The Deccan Traps, one of the largest volcanic features on Earth, is an example of a Large Igneous Province. The Traps consist of multiple layers of basalt, more than 2 km thick and cover an area over 500,000 sq km, and were formed as a result of volcanic eruptions in the Western Ghats about 66 million years ago. It is believed that the enormous volcanic eruptions led to global cooling of around 2C, and were instrumental in the mass extinction of non-avian dinosaurs.
Sedimentary Rocks
- Sedimentary rock is the type of rock formed sedimentation of material. This sedimentation can occur on the Earth’s surface or within bodies of water.
- Sedimentary rocks form the thin outermost layer of the earth’s crust, making up about 5% of the total volume of the crust.
- Sedimentary rocks are deposited in strata called bedding.
- Coal is a sedimentary rock.
- Examples of sedimentary rocks include shale, sandstone, limestone.
- The geological significance of Sedimentary Rocks is that they provide information about subsurface, which is important in civil engineering for construction of roads, bridges.
- Sedimentary rocks are also important sources of natural resources like fossil fuels, water, ores etc.
Sedimentary Rocks can be of three types:
Clastic Sedimentary Rocks
Clastic sedimentary rocks are those that are formed from rocks that have been broken down due to weathering, which are then transported and deposited elsewhere.
Organic Sedimentary Rocks
Organic sedimentary rocks contain materials generated by living organisms. They usually contain carbonate minerals generated by these organisms.
Chemical Sedimentary Rocks
Chemical sedimentary rocks are formed from minerals in solution that become oversaturated. They usually occur as a result of evaporation.
Did you Know?
Sedimentary rocks are the only rocks that contain fossils. Unlike igneous and metamorphic rocks, they form at temperatures and pressures that do not destroy fossils.
Metamorphic Rocks
- Metamorphic rocks form as a result of transformation of an existing rock, in a process called metamorphism. The existing rock is called protolith. Metamorphic rocks are formed when the protoliths are subject to extreme temperatures and pressures.
- They form from tectonic process, intrusion of magma, or simply by being deep beneath the earth’s surface (being subject to high temperatures and pressures of rock layers above)
- Much of the lower continental crust is metamorphic.
- Examples of metamorphic rocks include gneiss, slate, marble.
Types of Metamorphic Rocks
Contact Metamorphic Rocks
Contact metamorphic rocks are those that form when magma is injected into surrounding rock. The cooling magma leads to igneous rocks, and around this is a zone called contact metamorphism aureole where metamorphic rocks are formed.
Regional Metamorphic Rocks
Regional metamorphic rocks are those that form due to metamorphism over a wide area. Regional metamorphism tends to make rocks foliated.
Did You Know?
The Taj Mahal in India is made entirely of different types of marble, a metamorphic rock.
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