Rock And It's Types

Rock And It's Types

The hard and soft substances formed by the mixing of different types of minerals are called rocks, which are found in the earth's crust. The number of minerals in the earth's crust is more than 2000, out of which 24 minerals are called rock makers. Also, out of these 24 minerals, only 6 minerals are mainly found in rocks, which are associated with different mineral classes. In this, felspar, mica, quartz or rhinestone, pyranxium, olivine and amphibole are prominent. Apart from this, only 8 major elements are involved in the formation of these minerals, namely Oxygen (O2), Silicon (Si), Aluminum (Al), Iron (Fe), Calcium (Ca), Sodium (Na), Potassium (K) and Magnesium. ( Ma ) , is the contribution of . On the basis of the formation process, rocks are mainly divided into three classes, which are as follows –

1. Igneous rock
2. Sedimentary rock 
3. Metamorphic rock

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1. Igneous Rock

It is formed by the cooling of hot and liquid magma present under the crust. These are crystalline. These are also called primary rocks, because they were formed first after the formation of the earth. Sedimentary and metamorphic rocks are made of these. Chemical weathering has less effect on them. About 90% of the earth's crust is made up of igneous rocks. Fossils are not found in them and they are not flaky either. 

There are two types according to the position and structure.

• Intrusive Igneous  Rock 
• Plutonic Rocks
• Hypobyssal Rocks 
• Batholith
• Stoke
• Lacolith
• Lapolyth
• Phacolith
• Sill
• Dyke
• Extrusive Igneous Rock 

( a ) Intrusive Igneous Rock

When magma cools below the surface and takes a solid form, it is called an intrusive igneous rock. It has two forms.

• Plutonic Rocks
• Hypobyssal Rocks 
• Batholith
• Stoke
• Lacolith
• Lapolyth
• Phacolith
• Sill
• Dyke

                Earthquakes : Causes, Types andPrevention 

                Volcanoes and Its Types 

( i ) Plutonic Rock

It is formed deep inside the earth. It freezes slowly. Hence its crystals are big (Big Crystalls). Example – Granite

( ii ) Hypobyssal Rock

At the time of volcanic eruption, lava solidifies only in the cracks, holes and tubes due to surface barrier. Later these rocks appear on the surface as a result of the process of erosion. Example – dolerite, magnetite

Intermediate rocks (Hypobyssal Rocks) are also found in many major forms.

i. Batholith

It is a plutonic body, which is the largest igneous rock. It is basically made of granite and is dome shaped. Both its sides are raised and the upper floor is asymmetrical. It is found in the core of most of the mountains. Example – Coast Range (Canada – Largest), Idaho (USA)

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ii. Stoke

This is the form of batholith, which are small, less than about 100 sq km. Its upper part is domed.

iii. Lacolith

When magma rises to the upper layer, it solidifies in a domed form, it is called lacolith. This domed canopy is visible due to the rapid rise of magma. It is found in the western parts of North America.

iv. Lapolyth

When magma solidifies in a saucer shape, it is called a lapolyth. Many examples of this are found in South America.

v. Phacolith

When magma solidifies in a wavy shape, it is called a Phacolith.

vi. Sill

When magma solidifies parallel to the earth's surface, it is called a sill. Example – It is found abundantly in Chhattisgarh, Jharkhand. Its thickness ranges from one meter to hundreds of meters. Sill less than one meter is called sheet.

vii. Dyke

When magma solidifies in a vertical crack, it takes the form of a dyke. Example – Many dykes are found in Singhbhum district of Jharkhand.

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( b ) Extrusive Igneous Rock

Sometimes magma solidifies above the crust and forms the outer rock. Due to rapid solidification, their crystals are very small. These are also called volcanic rocks. Example – basalt, rhyolite

• The erosion of these rocks leads to the formation of Black Soil or Regur, which is suitable for cotton cultivation.
• When crystals do not grow in volcanic rocks, they are formed like glass. Example – obsidian, pitch stone, pumice, perlite

2. Sedimentary Rock

The rocks formed as a result of erosion and deposition of igneous and metamorphic rocks on the earth's surface are called sedimentary rocks. These are also called layered rocks. They are spread over about 75% of the entire crust, whereas only 5% are contributed to the formation. Rave is not found in these but it is added. It is soft as well as hard.

Sedimentary Rock Formation

Limestone – 8%, Sandstone – 12%, Shale – 80% (Component of Silt and Clay)

They are made in three ways.

Volcanoes and Its Types 

i. By Mechanical Action

• By wind – eg loess
• By Himani – Like Boulder Clay, Till
• By water – like sand stone, clay soil, boulder

ii. By Organic Matter

• By living beings – like Limestone, Chalk
• By plants – like peat, coal, lignite

iii. By Chemical Elements

Example – dolomite, rock salt, gypsum, limestone

3. Metamorphic Rock

Due to heat and pressure, the structure and form of igneous and sedimentary rocks changes. These are called Metamorphic Rocks. It is the hardest rock, and fossils are not found in it. Example -

• Due to Heat – Due to extreme heat as a result of volcanic action, limestone is converted into marble.
• Due to Pressure – neices and cysts are formed as a result of pressure generated due to compressional motion. Example – In the Himalayan and Rocky mountain countries.

Earthquakes : Causes, Types andPrevention 

Interchange of Rocks

1. Change from Sedimentary to Converted

• Shale –> Slate
• Limestone –> Marble
• chalk and dolomite –> marble
• Sandstone –> Quartzite
• Conglomerate –> Quartzite
• coal –> graphite, diamond
• Lignite coal –> Anthracite coal
• Bituminous Coal –> Graphite

2. Convert from Agneous to Aggressive

• granite –> gneiss
• basalt –> amphibolite, cist
• Grabo -> Serpentine

3. Convert from Converted to Converted

• slate –> phyllite
• Phyllite –> Cist
• Cyst –> Serpentine

In short – slate –> phyllite –> cist –> serpentine

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