PETROLOGY
#1

presented by….
V.ABHINAV KOUNDINYA

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PETROLOGY AND ITS DEFINITION
Petrology (from Greek: petra, rock; and logos, 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, texture,structure,physical properties, etc., of rocks .
Whereas PETROGRAPHY deals with the descriptive part of rocks and PETROGENY deals with the mode of formation of rocks. These two together makeup Petrology.
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. They are –
1) IGNEOUS ROCKS
2) SEDIMENTARY ROCKS and
3) METAMORPHIC ROCKS.
CLASSIFICATION CHART
IGNEOUS 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.
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.
METAMORPHIC ROCKS
Metamorphism literally means change.
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 and those formed from sedimentary rocks are called Parametamorphic rocks.
COMMON STRUCTURES OF IGNEOUS ROCKS
In Igneous rocks the common structures are :
Vesicular structure
Amygdaloidal structure
Columnar structure
Sheet structure
Flow structure and
Pillow structure
COMMON STRUCTURES OF SEDIMENTARY ROCKS
Structures in sedimentary rocks can be divided in to-
1)Primary structures (formed during deposition)
and
2)Secondary structures (formed after deposition).
COMMON STRUCTURES OF METAMORPHIC ROCKS
The most common structures found in metamorphic rocks are –
1)Gneissose type,
2)Schistose type and
3)Granulose type.
TEXTURE
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
TEXTURES OF IGNEOUS ROCKS
Textures based on the
1) Degree of Crystallinity
2)Granularity and
3)Shapes of Crystals.
TEXTURES OF METAMORPHIC ROCKS
1) Crystalloblastic and Palimpsest Textures
and
2)Xenoblastic and Idioblastic Textures.
ROCK CYCLE
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,durabiliy,colour,appeareance, workability, etc., These inherent characters of rocks are of chief concern for a civil engineer to judiciously assess the suitabilityoccuring at project site for required purpose.
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#2

petrologist - A geologist who specializes in petrology.Lithology was once approximately synonymous with petrography, but in current usage, lithology focuses on macroscopic hand-sample or outcrop-scale description of rocks, while petrography is the speciality that deals with microscopic details.Petrology is the study of rocks. This field is regarded as a subfield of geology or earth science, and people in this field are known as petrologists. There are a number of applications for petrology, including opportunities in the lab, field, and classroom for people with petrology degrees.
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