igneous rocks formation and their classification

Introduction to Rocks, Introduction to Igneous Rocks, Its formation, Classification, Properties, Chemical Composition

Presented by: Mazhar Gul Soomro (K13PG43)

Department of Petroleum And Natural Gas Engineering,

MUET S.Z.A.B Campus Khairpur Mir’s.

IGNEOUS ROCKS

ROCKS

Rock is Aggregate of one or more minerals. In common, Rock is anything which is hard and resistant. But in Geological language, rock’s meaning is extended to

include all the natural substances made of minerals either they are Hard like Granite or soft like sand or clay.

Rock and Stone: Anything which is hard and resistant may be named as Stone but Rock may be Hard or soft.

MAJOR FAMILIES OF ROCKS

Rocks are classified into Three Major Families:

I. Igneous Rocks

II. Sedimentary Rocks

III. Metamorphic Rocks.

Now, we are going to discuss Igneous Rocks which is our main topic.

Igneous rock Is defined below:

INTRODUCTION TO IGNEOUS ROCK

The Word Igneous is derived from Latin Word “IGNIS” means ‘Fire’.

These rocks are formed by the solidification of Magma or Lava. These Rocks are also known as Primary or First formed Rocks. When Magma is under the surface of earth it is called Magma. When it erupts out from volcanoes it is known as Lava.

PROCESS OF FORMATION OF IGNEOUS ROCKS As we go under the surface of earth, it is observed that Temperature

increases at every depth.

It is considered that 1ºC temperature increases on every 40m of depth.

Considering these facts we can say that a stage will come where the temperature will found to be 1000ºC. That stage should be at the depth of 40km.

At this depth all the substances will be in molten state.

A hot material or Liquid rock is found to be exists below the surface of the Earth, which is called Magma & when it is forced out at the surface of earth, it is known as Lava.

PROCESS OF FORMATION OF IGNEOUS ROCKS

As long as the physical and chemical conditions below the surface of earth remain unchanged, Magma remains in molten state.

But whenever these conditions change, magma is changed into Solid rock, which is called Igneous rock.

CLASSIFICATION OF IGNEOUS ROCKS

There are two Basic types of Igneous Rocks:

I. Intrusive Igneous Rocks (Intr: Inner action)

II. Extrusive Igneous Rocks (Extr: Outer action)

INTRUSIVE IGNEOUS ROCKS When Magma is solidified or crystallized below the surface of earth, the

igneous rocks are formed which are known as “Intrusive Igneous Rocks”.

Intrusive rocks are coarse grained crystals.

Pegmatite (An Intrusive igneous rock)

EXTRUSIVE ROCKS When Magma is forced out at the surface of earth, due to certain conditions,

it its solidified on the surface of earth and the rocks are formed on the surface of earth are know as “Extrusive Igneous Rocks”.

Extrusive rocks are less crystalline as compared to intrusive rocks.

Andesite (An Extrusive Igneous Rock)

CLASSIFICATION OF IGNEOUS ROCKS

Igneous rocks are classified into two main categories:

I. Classification based on the proportion of Silica as main constituent

II. Classification based on the basis of solidification of Magma

I. CLASSIFICATION BASED ON SILICA

On the basis of silica igneous rocks are classified into two types:

I. Acidic Rocks

II. Basic Rocks


I. Acidic rocks: Igneous rocks having high percentage of silica (more than 2/3%).

These rocks are light in color and weight.


II. Basic rocks: Igneous rocks which contain relatively low percentage of silica (Generally less than ½%).

These rocks are dark in color and heavier in weight than Acidic Rocks.

II. CLASSIFICATION ON THE BASIS OF SOLIDIFICATION OF MAGMA

On the basis of solidification of magma, igneous rocks are classified into following three types:

I. Plutonic Rocks

II. Hypabyssal Rocks

III. Volcanic Rocks


I. Plutonic Rocks: When Magma is solidified below the surface of earth, the rocks formed are know as Plutonic rocks.

• These are also called Intrusive Rocks.

• They take long time for Magma to cool and solidify into rocks.

II. Hypabyssal rocks: When Magma is solidified at short distance below the surface of earth (nearly at depth of 7km) are know as Hypabyssal rocks.

• These rocks are also called Intrusive Rocks.


III. Volcanic Rocks: When Magma is solidified on the surface of earth, the rocks are formed know as Volcanic rocks.

• These are also called Extrusive Rocks.

DESCRIPTION OF IGNEOUS ROCKS On the basis of properties of Igneous rocks they are classified into different

types, but most important one’s are given below:

Granite

Gabbro

Basaltic

Dolerite

Diorite

GRANITE Granite is common type of intrusive(Plutonic rocks).

It is light in color with pink to grey in color

This rock mainly consists of Quartz, feldspar and mica.

It used as most important building stone for the decorative, monumental and architectural purposes because of its light color.

GABBRO It is coarse grained, intrusive mafic Igneous rock which is chemically equivalent to basalt.

It is dark in color with grey to black.

It is used as road material and concrete aggregate.

It is also used in kitchen and their countertops. Also used widely as Graveyard headstone.

BASALTIC Basalt is common Extrusive igneous (volcanic) Rock formed by the rapid cooling of Lava.

It is usually grey to black in color.

It has fine-grained mineral texture.

It is used in construction (as building blocks or in groundwork).

It also used in construction of bridges, making cobblestones, in making statues.

DOLERITE Dolerite is mafic, holocrystalline, subvolcanic rock. It is also know as diabase.

It has dark brown color.

It is used as crushed stone and as ornamental stone.

DIORITE Diorite is an Intrusive Igneous rock.

It is grey to dark grey in color. It can also be black or bluish grey.

It is extremely hard rock.

Its hardness allows it to be worked finely and take a high polish, and to provide a durable finished work.

CHEMICAL COMPOSITION Chemical composition of igneous rocks:

• Aluminum Oxide (Al2O3) = 10-20%

• Silicon Oxide (SiO2) = 40-75%

• Metals (Ca, Mg, Fe) =10-15%

PROPERTIES OF IGNEOUS ROCKS

Most of igneous rocks are very important but Plutonic rocks having high crushing and sharing strength. It is used as satisfactory rock from all of the other rocks.

Igneous rocks are used in construction of buildings, road, bridges.

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igneous rocks formation and their classification

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