Petrology is the study of rocks and their origins, compositions, textures, and structures. There are three main types of rocks: igneous rocks formed from cooled magma, sedimentary rocks formed from compressed sediments, and metamorphic rocks formed from existing rocks subjected to heat and pressure. Rocks are constantly changing between these types through geological processes in the rock cycle, powered by Earth's interior heat and the energy from the sun. Igneous rocks can become sedimentary rocks through weathering and erosion then become metamorphic rocks through burial and increased heat and pressure, and metamorphic rocks can melt to form new magma and igneous rocks.

1. PETROLOGYPETROLOGY
Dr. P. Sarathbabu M.Sc. B.Ed. Ph.D.
Department of Geology
Acharya Nagarjuna University

2. Introduction: Petrology deals with the study of rocks
Petro = rock , ( litho=rock )
Logos = study
Petrology comprises the
Origin,
Association
Occurrence
Mineral composition
Texture
Structure
Physical properties etc.. of rocks

3. Rock: Aggregated solids of minerals is called rock.
(Or)
A rock may be defined as “an unit of the earth’s crust
All rocks are made of two or more minerals, but minerals are not made of
rocks.

4. Geological Classification of Rocks
• There are three main types of rocks:
1.1. IgneousIgneous - formed when molten rock
cools.
2.2. MetamorphicMetamorphic – rocks changed by the
effect of heat and pressure.
3.3. SedimentarySedimentary – formed by the
consolidation of sediments in the
layered or bedded rocks deposited in
the ocean bottom or huge lakes, etc.

5. What type of rock is formed
when magma cools and hardens?
Characteristics
A tough, frozen melt with little texture or layering;
mostly black, white and/or gray minerals; may look like
granite or like lava

6. What type of rock is formed
when change occurs from heat
and pressure in the Earth?
Characteristics
Hardened sediment with layers (strata) of sandy or
clayey stone; mostly brown to gray; may have
fossils and water or wind marks

7. What type of rock is formed when
weathering and erosion cause
sediments to press together in
layers?
Characteristics
Tough rock with layers (foliation) of light and dark
minerals, often curved; various colors; often glittery
from mica

8. Pegmatite
Dolerite
Charnockite
Laterite

9. Rock Cycle
• The three different types of
rocks--- igneous, sedimentary
and metamorphic---are
constantly being changed from
one type to another type
through various geological
processes.

10. Early stage of Earth = Molten stage

13. Volcanic Eruption
Lava flow

14. MAGMA
Crystallization
IGNEOUS

15. MAGMA
IGNEOUS
Plutonic
Crystallization

16. MAGMA
Volcanic
IGNEOUS
Plutonic
Crystallization

17. MAGMA
Volcanic
IGNEOUS
Plutonic
Uplift
Crystallization
Weathering

18. MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
Uplift
Crystallization
Weathering SEDIMENT

19. MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
SEDIMENTARY
Uplift
Crystallization
Weathering
Erosion
Transport
Deposition

20. MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
SEDIMENTARY
Uplift
Crystallization
Weathering
Erosion
Transport
Deposition

21. MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
SEDIMENTARY
METAMORPHIC
Uplift
Burial
Increased P&T
Crystallization
Weathering
Erosion
Transport
Deposition

22. MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
SEDIMENTARY
METAMORPHIC
Uplift
Burial
Increased P&T
Melting
Crystallization
Weathering
Erosion
Transport
Deposition
Can you see
any shortcuts?

23. MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
SEDIMENTARY
METAMORPHIC
Uplift
Burial
Increased P&T
Melting
Crystallization
Weathering
Erosion
Transport
Deposition

24. • The rock cycle demonstrates the
relationships among the three
major rock groups
• It is powered by the interior heat of
the Earth
• As well as earth’s momentum
and…
• The energy from the sun
• It involves processes on the
Earth’s surface as well as the
Earth’s interior
• It connects the “hydrologic cycle”
with the “tectonic cycle”.
In Conclusion…

26. MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
SEDIMENTARY
METAMORPHIC
Uplift
Burial
Increased P&T
Melting
Crystallization
Weathering
Erosion
Transport
Deposition

29. Granite

30. Marble

31. Sandstone

32. Civil Engineering importance of Petrology
• Petrology provides a proper concept and logical basis
for interpreting physical properties of rocks.
• The study of texture, structure, mineral composition,
chemical composition etc., gives all necessary details
regarding the strength,durabiliy,colour,appeareance,
workability, etc.,
These inherent characters of rocks are of chief concern for a
civil engineer to judiciously assess the suitability occurring at
project site for required purpose