SlideShare une entreprise Scribd logo
1  sur  25
Télécharger pour lire hors ligne
Classification Of Igneous Rocks
Saif Elden Abo Khashaba
Prepared by
Supervised by
Prof.Dr. Elmetwally Mohammed Lebda
Kafrelsheikh University
Faculty of science
Geology Department
2018
Classification of igneous rocks
 Classification of igneous rocks is one of the most confusing
aspects of geology.
 This is partly due to historical reasons, partly due to the nature of
magmas, and partly due to the various criteria that could
potentially be used to classify rocks.
 Igneous Rocks Are Most Classified Into Groups On The Basis Of :
Textures
Mode of occurrence
Chemical composition
Classification according to textures
 Phaneritic: rocks with mineral grains that are large enough to be identified by eye.
Slowly cooled intrusive rocks. Ex: gabbro and granite
 Aphanitic: rocks with grain too small to be identified by eye. Rapidly solidified extruded
magma and marginal facies of shallow intrusions. Ex: basalt and rhyolite .
 Porphyritic: bimodal grain size distribution. The large grains (phenocrysts) imbedded in
fine grains (ground mass)
 Glassy: no crystals formed due to very rapid cooling
 Pyroclastic: including the rocks come from explosive eruptions of lava into the air
resulting in fragmental, typically glassy material which fall as volcanic
ash, lapilli and volcanic bombs.
 Pegmatitic: very large xtals (cm to 10s of cm); i.e., slowly cooled, Forms veins or layers
within plutonic body
Classification according to mode of occurrence
A. Plutonic rocks (Intrusive):
• Igneous rocks of deep-seated origin
• They have phaneritic texture
• Generally medium to coarse grained in size (individual
crystal can be distinguished with the naked eyes).
• Examples: gabbro, diorite and granite
Classification according to mode of occurrence
B. Volcanic rocks (extrusive):
• Igneous rocks formed at or very near to the surface of the earth.
• They have aphanitic texture.
• very fine grained or glassy rocks (Most of the individual
crystals cannot be distinguished with naked eyes).
• Examples are basalt, andesite .and rhyolite
Classification according to chemical composition
1-Silica percentage (% SiO2)
 Felsic: feldspar + silica
~55-70% silica, K-feldspar > 1/3 of feldspars present
light-colored silicate minerals — Continental crust
 Intermediate: between felsic and mafic
~55-65% silica, plag > 2/3 of feldspars present
Na-rich plag predominates over Ca-rich plag
 Mafic: magnesium + ferric iron
~45-50% silica; Ca-rich plag dominant feldspar
dark silicate minerals — Oceanic crust
 Ultramafic: >90% mafic minerals, silica < 45%, few or no feldspars Mantle-derived
2- Silica saturation
The silica saturation concept can thus be used to divide rocks in silica
undersaturated, silica saturated, and silica oversaturated rocks. The first and last
of these terms are most easily seen.
This is an easy concept which leads to a simple classification that actually utilizes the
mineralogy of the rock.
 Rocks are classified into 3 groups:
 Saturated: Are rocks which do not contain either quartz or feldspathoids.
 Oversaturated: Are rocks containing quartz.
 Undersaturated: Are rocks which contain feldspathoids (no quartz).
In addition to Qz and feldspathoids, other minerals can be used to indicate the level of
silica saturation in a rock.
3-Alumina (Al2O3) Saturation
The concept of alumina saturation is based on whether or not there is an
excess or lack of Al to make up the feldspars.
 Note that Al2O3 occurs in feldspars in a ratio of 1 Al to 1 Na, 1K, or 1 Ca:
 KAlSi3O8 -- 1/2K2O : 1/2Al2O3
 NaAlSi3O8 -- 1/2Na2O : 1/2Al2O
 CaAl2Si2O8 -- 1CaO : 1Al2O3
 Three possible conditions exist:
1. If there is an excess of Alumina over that required to form feldspars, we say
that the rock is peraluminous.This condition is expressed chemically on a
molecular basis as:
Al2O3 > (CaO + Na2O + K2O).
3. Peralkaline:
 rocks are those that are oversaturated with alkalies (Na2O + K2O), and thus
undersaturated with respect to Al2O3.
 On a molecular basis, these rocks show: Al2O3 < (Na2O + K2O).
 Peralkaline rocks are distinguished by the presence of Na-rich minerals like
aegerine, riebeckite, arfvedsonite , or aenigmatite in the mode.
2. Metaluminous: rocks are those for which the molecular percentages are as follows:
Al2O3 < (CaO + Na2O + K2O) and Al2O3 > (Na2O + K2O).
 These are the more common types of igneous rocks That characterized by lack of an
Al2O3-rich mineral and lack of sodic pyroxenes and amphiboles in the mode
Classification of Igneous Rocks
Figure 2-4. A chemical classification of volcanics based on total alkalis vs.
silica. After Le Bas et al. (1986) J. Petrol., 27, 745-750. Oxford University
Press.
Classification according to mineral composition
Figure 2-1a. Method #1 for plotting a point with the components: 70% X, 20% Y, and 10% Z on
triangular diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall.
Classification of igneous rocks
Classification of igneous rocks
Classification of igneous rocks
Classification of igneous rocks
Classification of igneous rocks
BASALT – With or Without Useful Clues
As with the previous image, the sample on the left exhibits a few slightly larger olivine crystals
[green arrows], and probably has pyroxene as the other mineral. In the right sample, the purple
arrows point to amygdules, which are minerals precipitated in once-empty vesicles. Given that
they may have formed well after the lava cooled, and be unrelated to it, they are no indicator of
the lava’s composition.
BASALT – Clues in Vesicular Basalts
The scoria, or scoriaceous basalt, on the left has a few clues to its
chemistry. Many of the vesicles have a lining of pale pea-green
material [green arrows] often derived from the weathering of
olivine, and the iron content is confirmed by the reddish-brown
oxidized (rusted) weathered surface [red arrows]. The right
sample has obvious olivine crystals, perhaps phenocrysts, but no
lining to the vesicles.
BASALT – Pillow Basalt from a Mid-Ocean Ridge
Submarine eruption of basalt lavas leads to very rapid cooling of the exterior
surface, to produce a flexible skin that contains the lava. Successive eruptions
look like a stack of pillows, with rounded, convex upper surfaces. On the left
we see the fresh surface (broken and also cut with a rock saw) with the yellow
arrows pointing to the rapidly weathered exposed surface, seen on the right.
COLUMNAR BASALT
This outcrop is the Giant’s
Causeway in Ireland; the
Devil’s Post Pile is a
similar exposure in
California.
The polygonal columns result from cooling, contraction, and cracking of thin, widespread
sheets of mafic rock. These occur either by subaerial eruption of fluid basalt at rifts within
continents, or by intrusion of mafic magma as near-surface sills between layers of cooler
sediments.
BASALT
This is a porphyritic
basalt, whose
phenocrysts tell us
much about the
composition.
The plagioclase phenocrysts [red arrows] suggest this is mafic, not
ultramafic. As such, the matrix between the phenocrysts is likely a
mixture of pyroxene and plagioclase, without any appreciable olivine.
TRACHYTE – an Intermediate Volcanic Rock
The classic intermediate composition volcanic rock is andesite. These samples,
from the Crowsnest Pass, are alkali-rich (K, Na) intermediate rocks, whereas
true andesite would be higher in Ca. The black phenocrysts are garnet [yellow
arrows], with dodecahedral habit (the mafic minerals in intermediate rocks are
more typically amphibole or pyroxene). The pink phenocrysts [blue arrows] are
feldspar.
RHYOLITE
The lighter colour
is indicative of the
felsic composition
of this extrusive
rock, though we
cannot distinguish
the minerals.
We expect, based on its felsic composition, that it would have quartz and potassium feldspar,
and perhaps some mafic mineral content. The black spots [red arrows] are in fact not mafic
minerals, but small blobs of black volcanic glass, or obsidian, which itself is felsic.
RHYOLITE
This would normally
be called pumice, a
term that describes
the texture rather
than being a proper
rock name used in
classification.
It represents a case in which gas-rich felsic lava has turned into a
sort of sticky froth that has eventually hardened. Flow of this
taffy-like material has produced many glassy strands spanning the
vesicles [blue arrows]. It is otherwise like the previous sample.
OBSIDIAN
This rock would have erupted
as a rhyolite lava in the form
of pumice, then collapsed.
Rocks have minerals, which
are crystalline, yet this is
felsic volcanic glass, and is an
exception to the basis for
colour index.
There are no mafic minerals (or, technically, any other for that matter), so this rock has
a Colour Index of zero, even though it is completely black on the fresh surface. The
brown weathered surface is a clue to the presence of iron, dispersed through the glass to
make it black.

Contenu connexe

Tendances

Tendances (20)

7-Metamorphic Facies.ppt
7-Metamorphic Facies.ppt7-Metamorphic Facies.ppt
7-Metamorphic Facies.ppt
 
Komatiite
KomatiiteKomatiite
Komatiite
 
A seminar on ramsay classification of fold
A seminar on ramsay classification of foldA seminar on ramsay classification of fold
A seminar on ramsay classification of fold
 
Carbonate rocks
Carbonate rocksCarbonate rocks
Carbonate rocks
 
Ore deposits (contact metamorphism)
Ore deposits (contact metamorphism)Ore deposits (contact metamorphism)
Ore deposits (contact metamorphism)
 
Tecotnites
TecotnitesTecotnites
Tecotnites
 
Diversification of magma
Diversification of magmaDiversification of magma
Diversification of magma
 
Ch 02 igneous classification
Ch 02 igneous classificationCh 02 igneous classification
Ch 02 igneous classification
 
Migmatite and metamorphism
Migmatite and metamorphismMigmatite and metamorphism
Migmatite and metamorphism
 
SEDIMENTARY STRUCTURES
SEDIMENTARY STRUCTURESSEDIMENTARY STRUCTURES
SEDIMENTARY STRUCTURES
 
Sedimentary structure
Sedimentary structureSedimentary structure
Sedimentary structure
 
Classification of igneous rocks
Classification of igneous rocksClassification of igneous rocks
Classification of igneous rocks
 
Ophiolite
OphioliteOphiolite
Ophiolite
 
Lineation and their types
Lineation and their typesLineation and their types
Lineation and their types
 
METAMORPHIC DIFFERENTIATION
METAMORPHIC DIFFERENTIATIONMETAMORPHIC DIFFERENTIATION
METAMORPHIC DIFFERENTIATION
 
Residual Mineral Deposits
Residual Mineral DepositsResidual Mineral Deposits
Residual Mineral Deposits
 
Wall Rock Alteration
Wall Rock AlterationWall Rock Alteration
Wall Rock Alteration
 
STRATIGRAPHIC CORRELATION
STRATIGRAPHIC CORRELATION STRATIGRAPHIC CORRELATION
STRATIGRAPHIC CORRELATION
 
Hydrothermal deposits by VARINDRA
Hydrothermal deposits by VARINDRAHydrothermal deposits by VARINDRA
Hydrothermal deposits by VARINDRA
 
Ophiolite ppt
Ophiolite pptOphiolite ppt
Ophiolite ppt
 

Similaire à Classification of igneous rocks

Igneous_Rock_Classification.ppt
Igneous_Rock_Classification.pptIgneous_Rock_Classification.ppt
Igneous_Rock_Classification.pptAbineshG5
 
Lecture 23 - Igneous Rocks (1).ppt
Lecture 23 - Igneous Rocks (1).pptLecture 23 - Igneous Rocks (1).ppt
Lecture 23 - Igneous Rocks (1).pptbharatsingh300
 
01_Igneous Rock-Classification.pptx
01_Igneous Rock-Classification.pptx01_Igneous Rock-Classification.pptx
01_Igneous Rock-Classification.pptxAlMamun560346
 
Igneous_Rock_Textures.ppt
Igneous_Rock_Textures.pptIgneous_Rock_Textures.ppt
Igneous_Rock_Textures.pptMonuKumar183095
 
SEDIMENT-HOSTED DEPOSITS.pdf
SEDIMENT-HOSTED DEPOSITS.pdfSEDIMENT-HOSTED DEPOSITS.pdf
SEDIMENT-HOSTED DEPOSITS.pdfJulianISwandi
 
Minerals and rocks for presentations
Minerals and rocks for presentationsMinerals and rocks for presentations
Minerals and rocks for presentationsBelal El Nagar
 
Soil Forming Rocks and Minerals Classification
Soil Forming Rocks and Minerals ClassificationSoil Forming Rocks and Minerals Classification
Soil Forming Rocks and Minerals ClassificationDINESH KUMAR
 
Silica
SilicaSilica
Silicajo
 
Dacite power point presentation by Vasudevan M.pptx
Dacite power point presentation by Vasudevan M.pptxDacite power point presentation by Vasudevan M.pptx
Dacite power point presentation by Vasudevan M.pptxAnnamalai University
 
Belajar tentang batu andesit
Belajar tentang batu andesitBelajar tentang batu andesit
Belajar tentang batu andesithelmut simamora
 
UNDERSTANDING of FELDSPATHOID.pptx
UNDERSTANDING of FELDSPATHOID.pptxUNDERSTANDING of FELDSPATHOID.pptx
UNDERSTANDING of FELDSPATHOID.pptxmemukul2020
 
Economic geology - Magmatic ore deposits 2
Economic geology - Magmatic ore deposits 2Economic geology - Magmatic ore deposits 2
Economic geology - Magmatic ore deposits 2AbdelMonem Soltan
 
Lime stone and sandstone
Lime stone and sandstone Lime stone and sandstone
Lime stone and sandstone devi prasanth
 
The Geo-Chemistry of Igneous Rocks
The Geo-Chemistry of Igneous RocksThe Geo-Chemistry of Igneous Rocks
The Geo-Chemistry of Igneous Rocksedlaw
 
Marcus Geology Field Assignment Part I
Marcus Geology Field Assignment Part IMarcus Geology Field Assignment Part I
Marcus Geology Field Assignment Part Imroveracker
 
igneous rocks classification #6.pdf
igneous rocks classification #6.pdfigneous rocks classification #6.pdf
igneous rocks classification #6.pdfAdnanKhan153072
 

Similaire à Classification of igneous rocks (20)

Igneous_Rock_Classification.ppt
Igneous_Rock_Classification.pptIgneous_Rock_Classification.ppt
Igneous_Rock_Classification.ppt
 
Lecture 23 - Igneous Rocks (1).ppt
Lecture 23 - Igneous Rocks (1).pptLecture 23 - Igneous Rocks (1).ppt
Lecture 23 - Igneous Rocks (1).ppt
 
01_Igneous Rock-Classification.pptx
01_Igneous Rock-Classification.pptx01_Igneous Rock-Classification.pptx
01_Igneous Rock-Classification.pptx
 
Igneous_Rock_Textures.ppt
Igneous_Rock_Textures.pptIgneous_Rock_Textures.ppt
Igneous_Rock_Textures.ppt
 
SEDIMENT-HOSTED DEPOSITS.pdf
SEDIMENT-HOSTED DEPOSITS.pdfSEDIMENT-HOSTED DEPOSITS.pdf
SEDIMENT-HOSTED DEPOSITS.pdf
 
Ore deposits
Ore depositsOre deposits
Ore deposits
 
Minerals and rocks for presentations
Minerals and rocks for presentationsMinerals and rocks for presentations
Minerals and rocks for presentations
 
Soil Forming Rocks and Minerals Classification
Soil Forming Rocks and Minerals ClassificationSoil Forming Rocks and Minerals Classification
Soil Forming Rocks and Minerals Classification
 
igneous-petrology.ppt
igneous-petrology.pptigneous-petrology.ppt
igneous-petrology.ppt
 
Silica
SilicaSilica
Silica
 
Dacite power point presentation by Vasudevan M.pptx
Dacite power point presentation by Vasudevan M.pptxDacite power point presentation by Vasudevan M.pptx
Dacite power point presentation by Vasudevan M.pptx
 
Belajar tentang batu andesit
Belajar tentang batu andesitBelajar tentang batu andesit
Belajar tentang batu andesit
 
UNDERSTANDING of FELDSPATHOID.pptx
UNDERSTANDING of FELDSPATHOID.pptxUNDERSTANDING of FELDSPATHOID.pptx
UNDERSTANDING of FELDSPATHOID.pptx
 
Economic geology - Magmatic ore deposits 2
Economic geology - Magmatic ore deposits 2Economic geology - Magmatic ore deposits 2
Economic geology - Magmatic ore deposits 2
 
Lime stone and sandstone
Lime stone and sandstone Lime stone and sandstone
Lime stone and sandstone
 
The Geo-Chemistry of Igneous Rocks
The Geo-Chemistry of Igneous RocksThe Geo-Chemistry of Igneous Rocks
The Geo-Chemistry of Igneous Rocks
 
lec17.ppt
lec17.pptlec17.ppt
lec17.ppt
 
Marcus Geology Field Assignment Part I
Marcus Geology Field Assignment Part IMarcus Geology Field Assignment Part I
Marcus Geology Field Assignment Part I
 
igneous rocks classification #6.pdf
igneous rocks classification #6.pdfigneous rocks classification #6.pdf
igneous rocks classification #6.pdf
 
Lead And Zinc Deposits
Lead And Zinc DepositsLead And Zinc Deposits
Lead And Zinc Deposits
 

Dernier

Practical Research 1: Lesson 8 Writing the Thesis Statement.pptx
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptxPractical Research 1: Lesson 8 Writing the Thesis Statement.pptx
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptxKatherine Villaluna
 
How to Solve Singleton Error in the Odoo 17
How to Solve Singleton Error in the  Odoo 17How to Solve Singleton Error in the  Odoo 17
How to Solve Singleton Error in the Odoo 17Celine George
 
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdfMaximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdfTechSoup
 
Philosophy of Education and Educational Philosophy
Philosophy of Education  and Educational PhilosophyPhilosophy of Education  and Educational Philosophy
Philosophy of Education and Educational PhilosophyShuvankar Madhu
 
How to Add a New Field in Existing Kanban View in Odoo 17
How to Add a New Field in Existing Kanban View in Odoo 17How to Add a New Field in Existing Kanban View in Odoo 17
How to Add a New Field in Existing Kanban View in Odoo 17Celine George
 
In - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptxIn - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptxAditiChauhan701637
 
How to Add Existing Field in One2Many Tree View in Odoo 17
How to Add Existing Field in One2Many Tree View in Odoo 17How to Add Existing Field in One2Many Tree View in Odoo 17
How to Add Existing Field in One2Many Tree View in Odoo 17Celine George
 
Practical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptxPractical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptxKatherine Villaluna
 
What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?TechSoup
 
Diploma in Nursing Admission Test Question Solution 2023.pdf
Diploma in Nursing Admission Test Question Solution 2023.pdfDiploma in Nursing Admission Test Question Solution 2023.pdf
Diploma in Nursing Admission Test Question Solution 2023.pdfMohonDas
 
Easter in the USA presentation by Chloe.
Easter in the USA presentation by Chloe.Easter in the USA presentation by Chloe.
Easter in the USA presentation by Chloe.EnglishCEIPdeSigeiro
 
Quality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICEQuality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICESayali Powar
 
2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx
2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx
2024.03.23 What do successful readers do - Sandy Millin for PARK.pptxSandy Millin
 
CapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptxCapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptxCapitolTechU
 
Patterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptxPatterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptxMYDA ANGELICA SUAN
 
HED Office Sohayok Exam Question Solution 2023.pdf
HED Office Sohayok Exam Question Solution 2023.pdfHED Office Sohayok Exam Question Solution 2023.pdf
HED Office Sohayok Exam Question Solution 2023.pdfMohonDas
 
5 charts on South Africa as a source country for international student recrui...
5 charts on South Africa as a source country for international student recrui...5 charts on South Africa as a source country for international student recrui...
5 charts on South Africa as a source country for international student recrui...CaraSkikne1
 

Dernier (20)

Practical Research 1: Lesson 8 Writing the Thesis Statement.pptx
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptxPractical Research 1: Lesson 8 Writing the Thesis Statement.pptx
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptx
 
Prelims of Kant get Marx 2.0: a general politics quiz
Prelims of Kant get Marx 2.0: a general politics quizPrelims of Kant get Marx 2.0: a general politics quiz
Prelims of Kant get Marx 2.0: a general politics quiz
 
How to Solve Singleton Error in the Odoo 17
How to Solve Singleton Error in the  Odoo 17How to Solve Singleton Error in the  Odoo 17
How to Solve Singleton Error in the Odoo 17
 
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdfMaximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
 
Philosophy of Education and Educational Philosophy
Philosophy of Education  and Educational PhilosophyPhilosophy of Education  and Educational Philosophy
Philosophy of Education and Educational Philosophy
 
How to Add a New Field in Existing Kanban View in Odoo 17
How to Add a New Field in Existing Kanban View in Odoo 17How to Add a New Field in Existing Kanban View in Odoo 17
How to Add a New Field in Existing Kanban View in Odoo 17
 
Finals of Kant get Marx 2.0 : a general politics quiz
Finals of Kant get Marx 2.0 : a general politics quizFinals of Kant get Marx 2.0 : a general politics quiz
Finals of Kant get Marx 2.0 : a general politics quiz
 
In - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptxIn - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptx
 
How to Add Existing Field in One2Many Tree View in Odoo 17
How to Add Existing Field in One2Many Tree View in Odoo 17How to Add Existing Field in One2Many Tree View in Odoo 17
How to Add Existing Field in One2Many Tree View in Odoo 17
 
Practical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptxPractical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptx
 
What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?
 
Diploma in Nursing Admission Test Question Solution 2023.pdf
Diploma in Nursing Admission Test Question Solution 2023.pdfDiploma in Nursing Admission Test Question Solution 2023.pdf
Diploma in Nursing Admission Test Question Solution 2023.pdf
 
Easter in the USA presentation by Chloe.
Easter in the USA presentation by Chloe.Easter in the USA presentation by Chloe.
Easter in the USA presentation by Chloe.
 
Quality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICEQuality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICE
 
2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx
2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx
2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx
 
CapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptxCapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptx
 
Patterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptxPatterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptx
 
Personal Resilience in Project Management 2 - TV Edit 1a.pdf
Personal Resilience in Project Management 2 - TV Edit 1a.pdfPersonal Resilience in Project Management 2 - TV Edit 1a.pdf
Personal Resilience in Project Management 2 - TV Edit 1a.pdf
 
HED Office Sohayok Exam Question Solution 2023.pdf
HED Office Sohayok Exam Question Solution 2023.pdfHED Office Sohayok Exam Question Solution 2023.pdf
HED Office Sohayok Exam Question Solution 2023.pdf
 
5 charts on South Africa as a source country for international student recrui...
5 charts on South Africa as a source country for international student recrui...5 charts on South Africa as a source country for international student recrui...
5 charts on South Africa as a source country for international student recrui...
 

Classification of igneous rocks

  • 1. Classification Of Igneous Rocks Saif Elden Abo Khashaba Prepared by Supervised by Prof.Dr. Elmetwally Mohammed Lebda Kafrelsheikh University Faculty of science Geology Department 2018
  • 2. Classification of igneous rocks  Classification of igneous rocks is one of the most confusing aspects of geology.  This is partly due to historical reasons, partly due to the nature of magmas, and partly due to the various criteria that could potentially be used to classify rocks.  Igneous Rocks Are Most Classified Into Groups On The Basis Of : Textures Mode of occurrence Chemical composition
  • 3. Classification according to textures  Phaneritic: rocks with mineral grains that are large enough to be identified by eye. Slowly cooled intrusive rocks. Ex: gabbro and granite  Aphanitic: rocks with grain too small to be identified by eye. Rapidly solidified extruded magma and marginal facies of shallow intrusions. Ex: basalt and rhyolite .  Porphyritic: bimodal grain size distribution. The large grains (phenocrysts) imbedded in fine grains (ground mass)  Glassy: no crystals formed due to very rapid cooling  Pyroclastic: including the rocks come from explosive eruptions of lava into the air resulting in fragmental, typically glassy material which fall as volcanic ash, lapilli and volcanic bombs.  Pegmatitic: very large xtals (cm to 10s of cm); i.e., slowly cooled, Forms veins or layers within plutonic body
  • 4. Classification according to mode of occurrence A. Plutonic rocks (Intrusive): • Igneous rocks of deep-seated origin • They have phaneritic texture • Generally medium to coarse grained in size (individual crystal can be distinguished with the naked eyes). • Examples: gabbro, diorite and granite
  • 5. Classification according to mode of occurrence B. Volcanic rocks (extrusive): • Igneous rocks formed at or very near to the surface of the earth. • They have aphanitic texture. • very fine grained or glassy rocks (Most of the individual crystals cannot be distinguished with naked eyes). • Examples are basalt, andesite .and rhyolite
  • 6. Classification according to chemical composition 1-Silica percentage (% SiO2)  Felsic: feldspar + silica ~55-70% silica, K-feldspar > 1/3 of feldspars present light-colored silicate minerals — Continental crust  Intermediate: between felsic and mafic ~55-65% silica, plag > 2/3 of feldspars present Na-rich plag predominates over Ca-rich plag  Mafic: magnesium + ferric iron ~45-50% silica; Ca-rich plag dominant feldspar dark silicate minerals — Oceanic crust  Ultramafic: >90% mafic minerals, silica < 45%, few or no feldspars Mantle-derived
  • 7. 2- Silica saturation The silica saturation concept can thus be used to divide rocks in silica undersaturated, silica saturated, and silica oversaturated rocks. The first and last of these terms are most easily seen. This is an easy concept which leads to a simple classification that actually utilizes the mineralogy of the rock.  Rocks are classified into 3 groups:  Saturated: Are rocks which do not contain either quartz or feldspathoids.  Oversaturated: Are rocks containing quartz.  Undersaturated: Are rocks which contain feldspathoids (no quartz). In addition to Qz and feldspathoids, other minerals can be used to indicate the level of silica saturation in a rock.
  • 8. 3-Alumina (Al2O3) Saturation The concept of alumina saturation is based on whether or not there is an excess or lack of Al to make up the feldspars.  Note that Al2O3 occurs in feldspars in a ratio of 1 Al to 1 Na, 1K, or 1 Ca:  KAlSi3O8 -- 1/2K2O : 1/2Al2O3  NaAlSi3O8 -- 1/2Na2O : 1/2Al2O  CaAl2Si2O8 -- 1CaO : 1Al2O3  Three possible conditions exist: 1. If there is an excess of Alumina over that required to form feldspars, we say that the rock is peraluminous.This condition is expressed chemically on a molecular basis as: Al2O3 > (CaO + Na2O + K2O).
  • 9. 3. Peralkaline:  rocks are those that are oversaturated with alkalies (Na2O + K2O), and thus undersaturated with respect to Al2O3.  On a molecular basis, these rocks show: Al2O3 < (Na2O + K2O).  Peralkaline rocks are distinguished by the presence of Na-rich minerals like aegerine, riebeckite, arfvedsonite , or aenigmatite in the mode. 2. Metaluminous: rocks are those for which the molecular percentages are as follows: Al2O3 < (CaO + Na2O + K2O) and Al2O3 > (Na2O + K2O).  These are the more common types of igneous rocks That characterized by lack of an Al2O3-rich mineral and lack of sodic pyroxenes and amphiboles in the mode
  • 10. Classification of Igneous Rocks Figure 2-4. A chemical classification of volcanics based on total alkalis vs. silica. After Le Bas et al. (1986) J. Petrol., 27, 745-750. Oxford University Press.
  • 11. Classification according to mineral composition Figure 2-1a. Method #1 for plotting a point with the components: 70% X, 20% Y, and 10% Z on triangular diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall.
  • 17. BASALT – With or Without Useful Clues As with the previous image, the sample on the left exhibits a few slightly larger olivine crystals [green arrows], and probably has pyroxene as the other mineral. In the right sample, the purple arrows point to amygdules, which are minerals precipitated in once-empty vesicles. Given that they may have formed well after the lava cooled, and be unrelated to it, they are no indicator of the lava’s composition.
  • 18. BASALT – Clues in Vesicular Basalts The scoria, or scoriaceous basalt, on the left has a few clues to its chemistry. Many of the vesicles have a lining of pale pea-green material [green arrows] often derived from the weathering of olivine, and the iron content is confirmed by the reddish-brown oxidized (rusted) weathered surface [red arrows]. The right sample has obvious olivine crystals, perhaps phenocrysts, but no lining to the vesicles.
  • 19. BASALT – Pillow Basalt from a Mid-Ocean Ridge Submarine eruption of basalt lavas leads to very rapid cooling of the exterior surface, to produce a flexible skin that contains the lava. Successive eruptions look like a stack of pillows, with rounded, convex upper surfaces. On the left we see the fresh surface (broken and also cut with a rock saw) with the yellow arrows pointing to the rapidly weathered exposed surface, seen on the right.
  • 20. COLUMNAR BASALT This outcrop is the Giant’s Causeway in Ireland; the Devil’s Post Pile is a similar exposure in California. The polygonal columns result from cooling, contraction, and cracking of thin, widespread sheets of mafic rock. These occur either by subaerial eruption of fluid basalt at rifts within continents, or by intrusion of mafic magma as near-surface sills between layers of cooler sediments.
  • 21. BASALT This is a porphyritic basalt, whose phenocrysts tell us much about the composition. The plagioclase phenocrysts [red arrows] suggest this is mafic, not ultramafic. As such, the matrix between the phenocrysts is likely a mixture of pyroxene and plagioclase, without any appreciable olivine.
  • 22. TRACHYTE – an Intermediate Volcanic Rock The classic intermediate composition volcanic rock is andesite. These samples, from the Crowsnest Pass, are alkali-rich (K, Na) intermediate rocks, whereas true andesite would be higher in Ca. The black phenocrysts are garnet [yellow arrows], with dodecahedral habit (the mafic minerals in intermediate rocks are more typically amphibole or pyroxene). The pink phenocrysts [blue arrows] are feldspar.
  • 23. RHYOLITE The lighter colour is indicative of the felsic composition of this extrusive rock, though we cannot distinguish the minerals. We expect, based on its felsic composition, that it would have quartz and potassium feldspar, and perhaps some mafic mineral content. The black spots [red arrows] are in fact not mafic minerals, but small blobs of black volcanic glass, or obsidian, which itself is felsic.
  • 24. RHYOLITE This would normally be called pumice, a term that describes the texture rather than being a proper rock name used in classification. It represents a case in which gas-rich felsic lava has turned into a sort of sticky froth that has eventually hardened. Flow of this taffy-like material has produced many glassy strands spanning the vesicles [blue arrows]. It is otherwise like the previous sample.
  • 25. OBSIDIAN This rock would have erupted as a rhyolite lava in the form of pumice, then collapsed. Rocks have minerals, which are crystalline, yet this is felsic volcanic glass, and is an exception to the basis for colour index. There are no mafic minerals (or, technically, any other for that matter), so this rock has a Colour Index of zero, even though it is completely black on the fresh surface. The brown weathered surface is a clue to the presence of iron, dispersed through the glass to make it black.