2. IGNEOUS ROCKS
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.

3. 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.

5. 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:

6. 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.

7. 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.

8. 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.

9. 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)

10. 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)

11. 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)

12. 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

13. I.
CLASSIFICATION BASED ON SILICA
 On the basis of silica igneous rocks are classified into two types:
I.
Acidic Rocks
II. Basic Rocks

14. I.
CLASSIFICATION BASED ON SILICA
I. Acidic rocks: Igneous rocks having high percentage of silica (more than
2/3%).
These rocks are light in color and weight.

15. I.
CLASSIFICATION BASED ON SILICA
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.

16. 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

17. II. CLASSIFICATION ON THE BASIS OF
SOLIDIFICATION OF MAGMA
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.

18. II. CLASSIFICATION ON THE BASIS OF
SOLIDIFICATION OF MAGMA
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.

19. 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

20. 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.

21. 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.

22. 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.

23. 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.

24. 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.

25. CHEMICAL COMPOSITION
 Chemical composition of igneous rocks:
• Aluminum Oxide (Al2O3) = 10-20%
• Silicon Oxide (SiO2)
= 40-75%
• Metals (Ca, Mg, Fe)
=10-15%

26. 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.

27. Thanks for listening us
Any question?