1. Petrology
Kaustubh J. Sane
HJD Institute of Technical Education, Kera,

2. • Rock is a natural solid massive aggregate of
minerals forming the crust of earth.
• The branch of geology dealing with various
aspects of rocks such as their formation,
classification and occurrence is called
petrology.
• A civil engineer has to deal with rocks during
most of his life as materials for construction
and as sites for engineering structures.

3. • Volcanic rocks
• Plutonic rocks
• Hypabyssal rocks
Igneous rocks
• Clastic rocks
• Non-clastic chemically formed
• Non-clastic organically formed
Sedimentary
rocks
• Foliated
• Non-foliated
Metamorphic
rocks

4. Igneous rocks
• Broadly, all rocks which are formed from an
original hot, molten material through the
process of cooling and crystallization are
defined as igneous rocks.
• Hot molten material occurring naturally below
the surface of earth is called magma, and
which comes on surface and starts flowing
along it is called as lava.

5. • Volcanic rocks-
– Igneous rocks formed by the cooling and crystallization of lava
erupted from volcanoes.
– As lava cools down faster rate the grain size of crystals is fine and
often microscopic.
– The Deccan traps of India spread over more than 4 lakh km is best
example of volcanic igneous rocks.
– Rock types are;
• Basalt, Rhyolite, Dacite, Trachytes.
• Plutonic rocks-
– Rocks which are formed at an considerable depths-generally
between 7-10 km below surface are called as plutonic rocks.
– Due to slow rate of cooling grains are often coarse grain.
– Rock types are;
• Gabrro, granites, charnockites.
• Hypabyassal rocks-
– These are formed at intermediate stage below the earth surface.
– They show mixed characters of volcanic and plutonic rocks.
Rock types

6. • Textures of Igneous rocks
• Holocrystalline: crystallised
• Holohyaline: very fine size or glass
• Microcrystalline: intermediate size
Degree of
crystallization
• Coarse: grains above 5mm
• Medium: grains between 5 to 1 mm
• Fine: less than 1mm
Granularity
• Panidiomorphic: euhedral crystal
• Allotriomorphic: anhedral form
• Hypidiomorphic: show crystal of euhedra,
subhedra and anhedra form
Fabric

7. Holocrystalline
Holohyaline
Microcrystalline

8. Structures of Igneous rocks
Structure due to
mobility of Magma
• Flow structure:
formation of
parallel or nearly
parallel bands of
igneous bodies.
• Pillow structure
• Ropy lava
• Spherulitic
structure:
arrangement of
fibrous minerals
in radial manner.
Due to cooling of
magma
• Jointing structure
• Vesicular
structure
• Miarolitic
structures
Miscellaneous
structures
• Reaction rings
• Xenolithic
structure

10. Forms of Igneous Rocks
Extrusive
•Fissure
eruption
•Central
eruption
Intrusive
•Sills
•Dykes
•Lopoliths
•Laccoliths
•Phacoliths
•Batholiths

12. Sedimentary rocks

13. • Sedimentary rocks are formed due to simple
or complex mechanical and chemical
processes.
• Origin of rocks
– Provenance
– Transportation
– Deposition

14. Texture of rocks
• Size
– Coarse- gravel
– Medium- sand
– Fine- clay
• Boulder- minimum size 256mm
• Cobble- between 64 to 256mm
• Sand- less than 2mm
• Silt- 1/16 to 1/256mm
• Clay- less than 1/256

15. Rudaceous
•Conglomarate: loosely cemented heterogeneous material consisting of cobbles and pebbles.
•Breccia: coarser cemented angular fragments.
Arenaceous
• Sandstones: weathered sand sediments after natural compaction forms sandstones.
• Ferruginous: red brown color sst. Presence of iron containing minerals in cementation.
• Siliceous: sand grains are cemented with quartz.
• Calcareous sst: cemented with calcareous material
• Arkose: sst with 60% quartz and 40% feldspar.
Argillaceous
• Shale: laminated rock.
Calcareous
• Limestone: 93% CaCO3, 5% MgCO3; whitish color
• Dolomite: reverse of limestone. Blackish color
carbonaceous
• Peat
• Lignite
• Bituminous
• Anthracite

18. Metamorphic rocks

19. • Metamorphism denotes transformation of rocks
into new type by recrystallisation of their
constituents.
• The changes in metamorphism is due to
temperature and pressure conditions in crustal
layers 0f earth.
• Agents of metamorphism:
– Temperature
– Pressure
– Chemically active fluids

20. • The temperature increases in deeper parts of
crust.
• Pressure developed due to gravity results in
hydrostatic pressure. Which produces non-
uniform pressure, which changes the shape.
• Chemically active fluids are imp factors, they
occupies void spaces and fissures.

21. Structures in metamorphic rocks
• Cataclastic-
– Develops due to breakdown of fragmental rocks
by shearing.
– More resistant minerals undergoes less crushing;
other cases less resistant mineral undergoes
greater crushing.
– eg. mylonite

22. • Maculose-
– These is shown mainly by argillaceous rocks under
thermal and contact metamorphism.
• Schistose-
– Rocks show more or less parallel bands.
– Flaky minerals like biotite and hornblende under
temperature and pressure conditions form parallel
layered arrangements resulting in schistose structure.

23. • Granulose-
– These are formed due to presence of subhedral grain
minerals.
– It shows more or less uniform grain size.
– E.g. marble and quartzite.
• Gneissose-
– Formed due to alteration of schistose bands and
granulose structure.
– E.g. granite gneiss.

25. Classification of rocks
• Contact metamorphism
– In this process rise of temperature is dominant
factor. Thermal effects are influenced by the
contact zones of country rocks of igneous or
sedimentary types.
– Eg. Limestone – marble
sandstone – quartzite

26. • Regional metamorphism-
– Temperature and pressure affects a large regional
area.
– Shale---slate---phyllite---schist
• Dislocation metamorphism: