In this article of Geomorphology(Geography UPSC), nosotros will talk over the Classification of Rocks: Igneous, Sedimentary, and Metamorphic Rocks & Rock Cycle.

ROCK Arrangement

The Earth's chaff is made up of various types of rocks and the scientific study of rocks is called petrology.

These rocks differ in –

  • Texture – the caste to which something is rough or shine, or soft or hard
  • Structure – the fashion in which the parts of a system or object are arranged or organized, or a arrangement bundled in this mode
  • Mode of occurrence
  • Colour
  • Permeability – allows water, gas to pass
  • Caste of resistance to denudation

Co-ordinate to origin and appearance rocks tin be divided into 3 groups –

  1. Igneous rocks
  2. Sedimentary rocks
  3. Metamorphic rocks

IGNEOUS ROCKS

You can call back information technology by give-and-take ignite which means to fire. So, igneous rocks are formed after cooling and solidifying of molten rock (magma) from beneath the Globe's crust.

  • Rocks formed out of solidification of magma (molten rock below the surface) and lava (molten stone in a higher place the surface) and are known equally igneous or primary rocks.
  • Structure – crystalline
  • They do not occur in strata (layers) nor do they incorporate fossils.
  • These rocks tin be subdivided on the basis of mineral composition.
    • Acrid Igneous rocks
      • The high proportion of Silica
      • Less dense
      • Lighter colour than basic rocks
      • Example – Granite, quartz and feldspar
    • Basic igneous rocks
      • The low proportion of Silica
      • Denser and Dark colour
      • Example – Basalt, gabbro and dolerite

Classification of Igneous rocks on the ground of origin

  1. Plutonic Rocks or (Intrusive igneous rocks)
  2. Volcanic Rocks or (Extrusive igneous rocks)
IGNEOUS ROCKS

Plutonic Rocks or (Intrusive igneous rocks)

  • Formed – In-depth of world's crust
  • Commonly medium to coarse-grained texture due to tedious cooling.
  • Typically, light colour
  • Case – Granite, Diorite and Gabbro
  • Exposed at the surface past the process of denudation and erosion.

Volcanic Rocks or (Extrusive igneous rocks)

  • Sudden cooling of magma just below the surface or lava above the surface
  • Fine-grain considering of rapid cooling
  • Denser and darker in colour
  • Example – Basalt
  • Places where these are plant-
    • Antrim – Northern Ireland
    • Deccan plateau – India
    • Snake plateau – Columbia
  • Example of polygonal columns – Columnar basalt of Giant's Causeway in Antrim

SEDIMENTARY ROCKS

  • Sedimentary rocks are formed bylithification― consolidation and compaction of sediments.
  • Hence, they are layered or stratified of varying thickness. Case:sandstone, shale
  • Sediments are a result of denudation (weathering and erosion) of all types of rocks.
  • These types of rocks encompass 75 per cent of the earth's crust only volumetrically occupy only five per cent (considering they are available but in the upper office of the chaff).
  • Ice deposited sedimentary rocks are calledtill or tillite. Wind-deposited sediments are calledloess.
sedimentary rocks

Depending upon the mode of germination, sedimentary rocks are classified into:

  1. mechanically formed —sandstone, conglomerate, limestone, shale, loess.
  2. organically formed —geyserite, chalk, limestone, coal.
  3. chemically formed —limestone, halite, potash.

Mechanically formed sedimentary rocks

  • Formed by mechanical agents like running water, wind, ocean currents, ice, etc.
  • Example – Sandstone which is made of Sand grains, quartz fragments.
  • You have seen in Rajasthan and other places that sandstone is used to build homes.
  • Sandstone use –
    • Buildings
    • Grindstones
  • Sandstone types –
    • Dust – coarser type sandstone
    • Conglomerate – larger pebbles firmly cemented to form a stone
    • Breccia – when the fragments are angular
  • Clay – effectively sedimentary materials
    • Apply – brick making, shale or mudstone

Organically formed sedimentary rocks

  • Formed by – The remains of plants and animals are buried under sediments, and due to heat and pressure level from overlying layers, their composition changes.
  • Calcareous type rocks – limestone and chalk
    • Limestone (called as chuna in Hindi) – the one which is used in Pan and to whitewash home
  • Carbonaceous rocks – formed of vegetative matter
    • You know how coal is formed (a lot of pressure and rut compacted the plant remains into carbon which becomes peat, lignite or coal).

Chemically formed sedimentary rocks

  • Formed of – one kind or another solution which is precipitated chemically
  • Example –
    • Stone salt – derived from erstwhile sea bed or lakes
    • Gypsum – evaporation of Salt Lake.
    • Potash and nitrate are likewise obtained in a similar way.

METAMORPHIC ROCKS

  • The give-and-take metamorphic means 'change of grade'.
  • Metamorphism is a process by whichrecrystallisation and reorganization of  minerals occur within a stone. This occurs due to pressure level, volume and temperature changes.
  • When rocks are forced down to lower levels by tectonic processes or when molten magma rising through the crust comes in contact with the crustal rocks, metamorphosis occurs.
  • In the process of metamorphism in some rocks grains orminerals get arranged in layers or lines. Such an arrangement is calledfoliation or lineation.
  • Sometimes minerals or materials of unlike groups are arranged into alternating sparse to thick layers. Such a construction is chosen banding.
  • Gneissoid, slate, schist, marble, quartzite are some examples of metamorphic rocks.
  • Causes of Metamorphism
    • Orogenic (Mountain Building) Movements: Such movements often take place with an interplay of folding, warping and high temperatures. These processes requite existing rocks a new advent.
    • Lava Inflow: The molten magmatic material inside the earth's crust brings the surrounding rocks under the influence of intense temperature force per unit area and causes changes in them.
    • Geodynamic Forces: The omnipresent geodynamic forces such equally plate tectonics also play an of import office in metamorphism.

On the basis of the agency of metamorphism, metamorphic rocks can exist of 2 types

  1. Thermal Metamorphism
    1. The change of class or re-crystallisation of minerals of sedimentary and igneous rocks nether the influence of high temperatures is known as thermal metamorphism.
    2. A magmatic intrusion causing thermal metamorphism is responsible for the peak of Mount Everest consisting of metamorphosed limestone.
    3. Equally a effect of thermal metamorphism, sandstone changes into quartzite and limestone into marble.
  2. Dynamic Metamorphism
    1. This refers to the formation of metamorphic rocks under high pressure level.
    2. Sometimes loftier pressure is accompanied past loftier temperatures and the action of chemically charged water.
    3. The combination of directed pressure and heat is very powerful in producing metamorphism because it leads to more than or less complete recrystallisation of rocks and the product of new structures. This is known equally dynamo thermal metamorphism.
    4. Nether high pressure level, granite is converted into gneiss; clay and shale are transformed into schist.

Some examples of Metamorphosis

Igneous or Sedimentary stone Influence Metamorphosed rock
Granite Pressure Gneiss
Dirt, Shale Pressure Schist
Sandstone Heat Quartzite
Clay, Shale Oestrus Slate => Phyllite
Coal Heat Anthracite => Graphite
Limestone Heat Marble

Metamorphic Rocks in Bharat

  • The gneisses and schists are normally found in the Himalayas, Assam, W Bengal, Bihar, Orissa, Madhya Pradesh and Rajasthan.
  • Quartzite is a hard stone establish over Rajasthan, Bihar, Madhya Pradesh, Tamil Nadu and areas surrounding Delhi.
  • Marble occurs about Alwar, Ajmer, Jaipur, Jodhpur in Rajasthan and parts of Narmada Valley in Madhya Pradesh.
  • Slate, which is used as a roofing fabric and for writing in schools, is plant over Rewari (Haryana), Kangra (Himachal Pradesh) and parts of Bihar.
  • Graphite is establish in Orissa and Andhra Pradesh.

ROCK Cycle

  • Rock bicycle is a continuous procedure through which sometime rocks are transformed into new ones.
  • Igneous rocks are master rocks, and other rocks form from these rocks.
  • Igneous rocks can be changed intosedimentary or metamorphic rocks.
  • The fragments derived out of igneous and metamorphic rocks class into sedimentary rocks.
  • Sedimentary and igneous rocks themselves tin turn into metamorphic rocks.
  • The crustal rocks (igneous, metamorphic and sedimentary) may be carried down into the mantle (interior of the earth) through subduction process and the same meltdown and turn into molten magma, the source for igneous rocks
  • Example –
    • Clay → Slate
    • Limestone → Marble
    • Sandstone → Quartzite
    • Granite → Gneiss
    • Shale → Schist
    • Coal → Graphite (1 which is in our pencil)
ROCK CYCLE

Quiz:

Q1. Consider the following statements regarding the difference(s) betwixt extrusive and intrusive rocks?

  1. Extrusive rocks are fine grained, whereas intrusive rocks are coarse-grained.
  2. Extrusive rocks course over a much longer duration of time compared to intrusive rocks.

Which of the higher up statements is/are wrong?

a) ane only
b) ii only
c) Both 1 and two
d) Neither 1 nor 2

Solution: b)

The key difference between intrusive and extrusive rocks is that theintrusive rocks are formed from magma whereas the extrusive rocks are formed from lava.

Intrusive rocks: With no air to cool the magma,these rocks are formed very slowly. Composition of these rocks reflectspresence of large crystals. These crystals interlock to form the rock.

These rocks take a very large amount of time to solidify and they remain cached deep within the surface of the earth being surrounded by country rocks that have been at that place already.

Very slow cooling means thatthese rocks remain fibroid-grained.

Some of the perfect examples of intrusive rocks are the diorite, gabbro, and granite.

Much of the cadre of various mount ranges around the earth is made upwardly of these intrusive rocks.

Extrusive Rocks: Sometimes, molten rocks observe a way to come out of the surface of the earth through cracks and openings.

This magma flows in the course of lava and cools down apace as it comes into contact with air.

Igneous rocks that are formed from the magma that pours out of the surface of the earth are chosen extrusive rocks.

As these rocksabsurd down and solidify very rapidly, they exercise not get sufficient fourth dimension to form large crystals. Thus, they havesmall crystals and boast a fine texture.