geotechnics & applied geology 21306006

Om Institute Of Technology

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Subject: Geotechnics &

Applied Geology

Subject code: 21306006


2Shah Juhi

PRESENTATION ON:

PETROLOGY

Presented by:


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IndexPETROLOGY & its definitionGeological classification of rocksRock cycleCivil Engineering importance of PetrologyIgneous Rocks

Igneous Rock typesForms of Igneous RocksTexture of Igneous RocksStructure of Igneous Rocks

Metamorphic RocksStructures in metamorphic rocksTexture of Metamorphism RocksScope of Metamorphism petrology

Sedimentary RocksTexture of sedimentary rocksStructure of Sedimentary Rocks


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PETROLOGY & its definition

Petrology (from Greek: petra means rock and logos means knowledge) is the branch of GEOLOGY that studies rocks, and the conditions in which rocks form. The subject matter of PETROLOGY consists the origin, association, occurrence, mineral composition, chemical composition, formation, texture, structure, physical properties, types etc. of rocks .Whereas PETROGRAPHY deals with the descriptive part of rocks PETROGENY deals with the mode of formation of rocks. These two together makeup Petrology.

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•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.

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Geological classification of rocks

The rocks are classified in various ways based on different principles such as Physical, Chemical ‘n’ Geological Classifications. Among the different classifications. Geological classification of rocks is the most proper because grouping of rocks is more logical , less ambiguous, orderly and comprehensive. The Geological classification of rocks is based on their MODE OF ORIGIN. Their classification is.....

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Rock cycle

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Civil Engineering importance of Petrology

Petrology is very important from civil engineering point of view, as it 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, durability, colour, appearance, 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.

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Om Institute Of TechnologyIgneous Rocks

These are primary rocks, Most abundant rocks in the earth’s crust.These are formed at a very high temperature and pressure conditions directly as a result of solidification of magma or lava.

MAGMA: The term magma is applied when the melt is underground.

LAVA: The melt when it reaches the earth’s surface and flows over it, is called lava.

SOME IGNEOUS ROCKS

COOLING OF LAVA

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•EXTRUSIVE ROCKS•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, Andesite.•INTRUSIVE ROCKS•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;

• Granites, Syenites, Diorites, Gabbros, Peridotites.•Hypabyassal rocks-– These are formed at intermediate stage below the earth surface.– They show mixed characters of volcanic and plutonic rocks.

• Dolerites.

Igneous Rock types

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Forms of Igneous Rocks

Extrusive

Lava flows Pyroclastics

Intrusive

Sills Dykes Lopoliths LaccolithsPhacolithsBatholiths

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Texture of Igneous Rocks

Textures based on the1) Degree of Crystallinity2)Granularity and3)Shapes of Crystals.

The size, form and orientation of clasts or minerals in a rock is called its texture. The texture is a small-scale property of a rock, but determined many of its large-scale properties, such as the density, porosityy or permeabililty

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In Igneous rocks the common structures are :

Vesicular structure Amygdaloidal structure Columnar structure Sheet structure Flow structure and Pillow structure

Structure of Igneous Rocks


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Metamorphic Rocks

Metamorphism (from Greek: Meta=change & morphic=form)The change in pre-existing rocks under the influence of temperature, pressure and chemically active solutions.The metamorphic rocks formed from igneous rocks are called Orthometamorphic rocks .Those formed from sedimentary rocks are called Parametamorphic rocks.

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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

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•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.

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•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.

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1) Crystalloblastic2) Palimpsest Textures3) Xenoblastic4) Idioblastic Textures.

Texture of Metamorphism Rocks

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Scope of Metamorphism petrology Metamorphic petrology is the study of the subsolidus changes that a rock undergoes when exposed to physicochemical conditions different from those prevailing near the surface of the Earth. Metamorphism produces changes in mineral assemblages and textures that reflect re-equilibration of the rock to the new physicochemical conditions, i.e., minimization of the energy of the system.Metamorphism is commonly isochemical (except for volatile components, e.g., H2O, CO2). Where the system is open, the process is referred to as metasomatism.


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Sedimentary Rocks

Sediments are the products of weathering. Since these are secondary materials(i.e., derived from pre-existing rocks), the rocks formed out of them are called sedimentary or secondary rocks.The origin of sedimentary rocks is totally related to the weathering influence on rocks.

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Texture of sedimentary 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

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Structures in sedimentary rocks can be divided in to-1)Primary structures (formed during deposition) 2)Secondary structures (formed after deposition).

Structure of Sedimentary Rocks


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