Igneous Textures and Classification - Brock University · Igneous Textures and Classification ERSC 2P17 Brock University Igneous Textures • The texture of a rock is defined as:

Igneous Texture and Classification 9/13/2005

1

ERSC 2P17 Brock University

Igneous Textures and Classification


Igneous Textures• The texture of a rock is defined as:

– ______________________________________________________________________________

• In the case of the igneous rocks the texture is largely determined by the______ ______ of the magma that resulted in the specimen being examined


Igneous Textures• Examining igneous rocks reveals that they

may consist of:– ___________ grains which may be;

• large or small or a mixture of both• _______________________________

– solid _________• _______________________________

– individual ______ __________ packed together• _______________________________


2


Igneous Textures• The rate at which a magma cools controls:

–

–• ___________________ = glassy• ___________________ = crystalline• ____________________= mix of both


Igneous Textures• For slow cooling many mineral grains

________ and ______, with the rate of cooling controlling the final size of the mineral grains

• Grain size– _______________ < 1 mm

• _______ (cannot be distinguished with unaided eye)– _______________ 1-5 mm

• __________– _______________ > 5 mm

• ___________


Glassy = Fast

Cooling


3


Fine Grained


Medium Grained


Coarse Grained


4


Coarse Grained


Very Coarse Grained =Very Slow Cooling


Igneous Textures• The degree of crystal development reflects

how a mineral nucleated and grew and the ratio of solid to liquid at the time of growth

• Grain shape– __________

• composed of good crystal faces– __________

• some good crystal faces– __________

• no good crystal faces


5


Euhedral


Subhedral


Anhedral


6


Igneous Textures• Some igneous melts cool in two stages,

reflecting changes in the conditions under which the magma exists

• Resulting rocks typically have two different sizes of grains and are called ____________

• The large grains are referred to as ____________ and they are set in a finer grained ___________


Porphyritic Textures_____________________________________________

__________

________


Porphyritic TexturesLarge grains (Phenocrysts) in a finer grained matrix

PhenocrystsMatrix


7


Porphyritic TexturesLarge grains (Phenocrysts) in a finer grained matrix

Phenocrysts

Matrix


Igneous Textures• Vesicles - _________________• Amygdules - ______________

Vesicles

Amygdules


Plutonic Rock Types

(Intrusive Rocks)


8


Hornblende Syenite

Nepheline Syenite

Syenite• Major Minerals:

– _____________– _____________

• NO QUARTZ• Accessories:

• ________, ________, ___________


PT-190 Granodiorite• Major Minerals:

– ______________– ______________

• up to 10% quartz• Accessories:

– ______, _________BUPI 67


BUPI 59 Granite• Major Minerals:

– ____________– ____________– __________

• Accessories:– ______, _________,

__________

2002-6


9


Gabbro• Major Minerals:

– __________– __________

• Accessories:– _________, ______,

________

2000-2


Ultramafic• Major Minerals:

– _________– _________– _________

• Accessories:– __________

PT-175


Volcanic Rock Types

(Extrusive Rocks)


10


86-1

PI-4-2

Rhyolite• Major Minerals:

– _____________– _____________– ____________

• Accessories:– ______, _________,

_________


88-23

86-27

Dacite• Major Minerals:

– ___________– ___________– up to 15% ______

• Accessories:– ______, _________,

__________


86-72

86-73

Andesite• Major Minerals:

– ___________– ___________– _______

• Accessories:– _________

• Minor:– ______,

_____________


11


PT-96

90-132 Basalt• Major Minerals:

– __________– __________– _______________

• Accessories:– ______, _________


Ultramafic• Major Minerals:

– __________– __________

• Accessories:– ______,

__________


Feldspar Coarse Fine Coarse Fine Coarse FineK-feldspar> plagioclase

Granite Rhyolite Syenite Trachyte Nepheline Syenite Leucite Syenite

Phonolite Leucite Phonolite

Plagioclase> K-feldspar

Granodiorite Dacite Monzonite Latite Nepheline Monzonite

Plagioclase (oligoclase or andesine)

Tonalite Quartz Andesite

Monzodiorite Latite Basalt

Nepheline Diorite

Plagioclase (labradorite to anorthite)

Quartz Diorite

Andesite Gabbro Peridotite (ol dominant)

Basalt Nepheline Gabbro

Tephrite

No Feldspar Pyroxenite Hornblendite

Komatiite Ijolite Nephelinite

Quartz > 5% No Quartz, No Feldspathoid Feldspathoid > 5%Simplified Classification of Igneous Rocks


12


(1) If biotite is the dominant mafic mineral, constituting < 10%, the

rock is termed a Trondhjemite.

(3)The type of alkali feldspar

should be specified if

possible, e.g., Microcline

granite.

Q

PA(3)

90

60

20 35 65 90

Quartz-richgranitic rocks

Granite

Granodiorite

Tonalite (1)

Alka

li-fe

ldsp

ar g

rani

te

Percentage of Plagioclase

Perc

enta

ge o

f Qua

rtz

Quartzsyenite

Quartzmonzonite

Quartzmonzodiorite

or quartzmonzogabbro

Syenite Monzonite Monzodiorite ormonzogabbro

Alk-

feld.

qtz

syen

ite

Quartz diorite orquartz gabbro (2)

Diorite orgabbro

Alk-feldsyenite

(2) With < 5% mafic minerals, the rock is anorthosite. With

>40% mafic minerals, it is typically gabbro. Rocks with

5-40% mafic minerals are either diorite or

leucodiorite, and require determination of the

plagioclase content with the limiting composition being

An50.

IUGS Classification of Igneous Rocks


(1) If biotite is the dominant mafic mineral, constituting < 10%, the

rock is termed a Trondhjemite.

(3)The type of alkali feldspar

should be specified if

possible, e.g., Microcline

granite.

(4) The feldspathoid should be specified in each rock name; e.g., Nepheline

syenite

(2) With < 5% mafic minerals, the rock is anorthosite. With

>40% mafic minerals, it is typically gabbro. Rocks with

5-40% mafic minerals are either diorite or

leucodiorite, and require determination of the

plagioclase content with the limiting composition being

An50.

Q

P

F(4)

A(3)

90

60

20 35 65

10 50

90

90

Quartz-richgranitic rocks

Granite

Granodiorite

Tonalite (1)

Alka

li-fe

ldsp

ar g

rani

te

Percentage of Plagioclase

Perc

enta

ge o

f Qua

rtz

Quartzsyenite

Quartzmonzonite

Quartzmonzodiorite

or quartzmonzogabbro

Syenite Monzonite Monzodiorite ormonzogabbro

Alk-

feld

.qt

z sy

enite

Quartz diorite orquartz gabbro (2)

Diorite orgabbro

Foid-bearingsyenite

Foid-bearingmonzonite

Foid-bearingmonzodiorite ormonzogabbro

Foid-bearingdiorite orgabbro35 65

Foid-bearingalk-feldspar

syenite

Foidmonzosyenite

Foid monzodioriteor foid monzogabbro

Foidilite(as nephelinite, etc.)

Foid syenite

Foid

dio

rite

or fo

id g

abbr

o

Alk-feldsyenite

(file=iugsclas.ds4)

IUGS Classification of Igneous Rocks


Pl

OlPx

90

65

35

10 10

35

65

90

OlivineGabbronorite

Plag. bearing ultramafic rocks

Gabbronorite Troctolite

Anorthosite(plagioclasite) Anorthosite

Gabbroids

Ultramafic rocks

(leuco-)

(mela-)

Anorthosite

(leuco-)

(mela-)

Gabbroids

Ultramafic rocks

Pl

Px

65

35

10

90

Hbl1010

10

35

65

90

Gabbronorite

Anorthosite(plagioclasite)

Pyroxene -hornblende

gabbronorite

Hornblendegabbro

plag.-bearinghbl pyroxenite

plag.-bearingpx hornblendite

plag.-bearinghornblendite

plag.-bearingpyroxenite

Pl Pl

Opx Cpx

Gabbronorite

Plag.-bearing pyroxenites

GabbroNorite

(file=iugsclas.ds4)

Gabbroic rocksplagioclase +

pyroxene + olivine

Gabbroic rockscontaining hornblende

Gabbroic rocksplagioclase +

orthopyroxene +clinopyroxene

IUGS Classification of Mafic Igneous Rocks

Documents

Igneous Textures and Classification - Brock University · Igneous Textures and Classification ERSC 2P17 Brock University Igneous Textures • The texture of a rock is defined as: