In this presentation we have described igneous rocks, their composition, their types and their uses in various fields of engineering.

1. ENGINEERING GEOLOGY PRESENTATION
NAME: MOHAMMAD ASRAR SHAH
CLASS: CIVIL B
SEMEMSTER: II
RRN:170011601049
IGNEOUS ROCKS

2. DEFINITION:
Igneous rock or magmatic rock (derived from
Latin word ‘IGNIS’ meaning fire) is one of the
three main rock type, the others being
sedimentary and metamorphic. Igneous rock is
formed through the cooling and solidification
of magma or lava.
COMPOSITION:
The great majority of the igneous rocks are
composed of silicate minerals (meaning that
the basic building blocks for the magmas that
formed them are made of silicon [Si]
and oxygen [O]), but minor occurrences of
carbonate rich igneous rocks are found as well.

3. TEXTURES:
The main factor that determines the texture of an igneous rock is
the cooling rate (dT/dt). Other factors involved are :
The diffusion rate, The rate of nucleation of new crystals, The rate of
growth of crystals.
Depending upon the rate at which temperature is
lowered below the crystallization temperature. Three
types of textures exist:
1. For small degrees of undercooling the crystals will have a coarse
grained texture called phaneritic texture.
2. For larger degrees of undercooling, the crystals will have a fine
grained texture. the texture is said to be aphanitic.
3. At high degrees of undercooling, the crystals will have a glassy
texture called holohyaline texture.

4. STRUCTURE:
Igneous structures are mostly classified into three major groups, as follows:
1. Mega-structures: These are usually formed in the flow stage of the
magma.
2. Minor structures: These structures are formed in the fluid stage of the
magma.
3. Micro-structures: These are formed due to reaction between already
solidified crystals and the rest of the magma.

5. CLASSIFICATION:
Igneous rocks can be classified according to chemical or mineralogical parameters.
CHEMICAL:
1. Felsic igneous rocks containing a high silica content (examples granite )
2. Intermediate igneous rocks containing between 52–63% SiO2 (example andesite)
3. Mafic igneous rocks have low silica 45–52% (example gabbro and basalt)
4. Ultramafic rock igneous rocks with less than 45% silica (examples picrate and
peridotite)
MINERALOGIC:
1. Felsic rock, highest content of silicon, with predominance of quartz and
alkali feldspar (E.g., granite)
2.Mafic rock, lesser content of silicon relative to felsic rocks, with predominance of mafic
minerals (E.g, basalt and gabbro)
3.Ultramafic rock, lowest content of silicon, with more than 90% of mafic minerals
(e.g., dunite).

6. TYPES:
Igneous rocks are of two types, intrusive (plutonic rocks) and extrusive (volcanic
rocks).
Intrusive Igneous Rocks
Intrusive igneous rocks are formed when the magma cools off slowly under the
earth’s crust and hardens into rocks. Gabbro and granite are examples of
intrusive igneous rocks. Intrusive rocks are very hard in nature and are often
coarse-grained.
Extrusive Igneous Rocks
Extrusive igneous rocks are formed when molten magma spill over to the
surface as a result of volcanic eruption. The magma on the surface (lava) cools
faster on the surface to form igneous rocks that are fine grained. Examples of
such kind of rocks include pumice, basalt, or obsidian.

7. Examples of Igneous Rocks
1. GRANITE 2.BASALT 3.DIORITE

8. Thank you