the presentation is shared with public so they can get any help if needed about igneous rocks.

1. By: Hasan javed

3. Igneous rocks are formed when magma(molten rock) solidifies at
or under the surface of earth.
o TYPES
There are two types of igneous rocks:
- Intrusive igneous rocks(also called plutonic rocks)
 Formed when magma solidifies under the surface of earth.
 Composed of coarse grained rocks , with grain size > 1mm.
 The crystalline grains of plutonic rocks are commonly
interlocked in mosaic pattern.
- Extrusive igneous rocks(also called volcanic rocks)
 Formed when magma solidifies at the surface of earth.
 Composed of fine grained rocks, with grain size < 1mm.

4. Igneous rocks names are based on:
- Mineralogical composition
- Textural classification
• Textural classification:-
Because of their larger grain size, plutonic rocks can be easily identified
from volcanic rocks. Both differ in grain size as well as cooling rate.
• Mineralogical composition:-
Rocks can be mine rally classified as:
- Felsic rocks(having higher silica content i-e up to 70% & light colored
minerals) includes granite-rhyolite.
- Mafic rocks(composed of ferromagnesian silicates & are dark colored,
contains low silica content ~50%) includes gabbro-basalt.
- Intermediate rocks(containing almost equal amount of felsic & mafic
minerals with silica content b/w 53-65%) includes diorite-andesite.
- Ultramafic rocks(rich in iron and magnesium silicates with silica content
< 45%) includes peridotite.

5. BASALT
Mafic = Dark color
Fine grained= Small crystals
Extrusive = Small crystals = Formed
on surface
DIORITE
Felsic = Light color
Coarse grained= Large crystals
Intrusive = Large crystals = Formed
underground

6. PUMICE
Felsic = Light color
Fine grained= Small crystals
Extrusive = Small crystals = Formed
above ground
GABBRO
Mafic = Dark color
Coarse grained= Large crystals
Intrusive = Large crystals = formed
underground

8. Magma type SiO2 content Classification General color
Rhyolitic > 70% Felsic Light
Andesitic ~ 60% Intermediate ½ light ½
dark
Basaltic < 50% Mafic Dark
0% Ultramafic Dark /
Green

9. • Intrusions or intrusive structures are bodies of intrusive
rocks whose names are based on their shape and size
as well as their relationships to the surrounding rocks.
• Intrusion can either be deep or shallow depending on the
depth at which magma cools/solidifies.
- Dike:-
Dike is a tabular, discordant intrusive structure.
Discordant means that body is not parallel to any layering
in the country rock.
- Sill:-
Sill is also a tabular structure but it is concordant i-e
layering is parallel to country rock.

11. - Pluton:-
Pluton is a body of magma that crystallizes at a considerable
depth with in the surface of earth.
- Stock:-
A stock is a small discordant with a small outcrop area < 100
square kilometers.
- Batholiths:-
if outcrop area exceeds than 100 square kilometers, this large
discordant body is called batholith.
- Diapirs:-
These are the large blobs of magma , that are less dense than
surrounding rocks and rises up to upper crust due to this low
density.

13. • Granite is the most abundant igneous rock in mountain
ranges. It is also the most abundant igneous rock found
in lowland continents.

14. If a rock is heated sufficiently , the rock begins to melt to
form magma. Under ideal conditions, the rock can melt and
yield a granitic magma at temperatures as low as 625
degree centigrade, whereas temperature of more than
1000 degree centigrade is required to form basaltic
magma.
- HEAT FOR MELTING ROCK :-
Most of the heat that contributes to the generation of
magma comes from the very hot earth’s core, which is
brought to surface by:
- Conduction through mantle and crust.
- Convection currents
- Or by geothermal gradient.

15. • The temperature at which solid rocks start to change their form into magma (or
starts melting).
- FACTORS:-
- Pressure
- Water vapors
- Mixed minerals
 Pressure
The melting temperature increases with increasing pressure. The rocks that are
deep inside earth require high pressure to melt than those at the surface.
 Water vapors
High vapor pressure can significantly lower the melting temperature. Water
pressure sealed in under high pressure by overlaying rocks help break crystal
structures.
 Mixed minerals
Few combinations of minerals can significantly lower the melting temperature
from 100-200 degree centigrade.

17. • Explains the order in which minerals crystallize out of
magma solution.

18. Left side
- Iron-rich minerals
- Discontinuous Crystallization
Right side
- Feldspar minerals
- Continuous crystallization

19. • Magma can be evolved by:
- Mixing of magma
- Assimilation
- Differentiation
- Partial melting

20. Plate tectonics occur at three regions where igneous
activity may happen.
- Divergent boundary(associated with gabbro & basalt)
- Convergent boundary(associated with granite & andesite)
- Subduction zone (zone where felsic igneous rocks are
formed)

23. • A hill or a mountain formed by the extrusion of lava or
ejection of rock fragments from vent.
• Lava:-
Magma does not always reach the surface without
solidifying but when it does, its called lava.
• Pyroclast:-
The rock fragments burst into the air by the gases
entrapped by Lava. Pyroclastic debris is known as tephra .
• Lava flows:-
Outpouring of lava extended to earth’s surface.

26. • The opening of a volcano where the magma escapes to
reach the earth’s surface

27. • The steep walled depression around a volcanoes vent.

28. heat and pressure changes the rock to melt forming
liquid magma.
Magmas less dense than rock, forced slowly towards
earth’s surface.

29. • They often occur when Earth’s
tectonic plates:
• Move apart – divergent boundary
• Move towards each other – convergent
boundary
• At “Hot Spots” – where crust of Earth is
thinner than normal

30. • Shield volcanoes:-
Shield volcanoes are broad gently sloping cones
constructed of solidified lava. During eruption the lava
spreads quickly due to its low viscosity.
• Cinder cones:-
Cinder cone is a volcano constructed of pyroclast
ejected from the central vent.
• Strato volcano:-
Its also called composite volcano. It is formed from the
alternative layering of pyroclastics and rock solidified from
the lava flows.

33. - Circum pacific belt
- Mediterranean belt

34. • Volcanic domes are steep sided dome or spine shaped
masses of volcanic rocks formed from viscous lava that
solidifies in or above the volcanic vent.

35. • Volcanic rock in parallel, usually vertical columns, mostly
six sided; also called columnar jointing.