igneous classification

7/25/2019 Igneous Classification

1/11

Plotting on ternary diagrams 1

Method for plotting a

point with the

components:70% X,20% Y, and 10% Z on

trianglar diagrams!

"or each component,

yo always measrefrom #ero of that

component $opposite

side toward the corner

of that component!&f done correctly, the

lines for all '

components shold

cross at the same point!


2/11

(he plotting position for

this point is:

X )ale * X+$XYZ

Y )ale * Y+$XYZ

Z )ale * Z+$XYZ

-here X, Y, and Z are

the nmerical )ales of

the three plotted

components $e!g!, weight

% of .i/2, l2/', and"e/ in a chemical

analysis, or art#,

lali feldspar, or

Plagioclase in a mode

for this one oint!

Plotting on ternary diagrams 2


3/11

Plotting on ternary diagrams 'nother method for

plotting a point with the

components: 70% X,

20% Y, and 10% Z on

trianglar diagrams!

(he X component line

is drawn at 70% X lie

the pre)ios two slides!(he second line is radial

from X to the position

3etween Y and Z

determined 3y:

Y+$YZ

(his is especially sefl

for the &45.

classification diagrams


4/11

6lassification of pltonic ocs:

P" classification scheme for

coarse8grained igneosrocs that ha)e more than

10% $9art# feldspar

feldspathoids! (he odd

names are mostly from theancient history of natral

science!

Quartz-richGranitoid

9090

6060

2020Alkali Fs.Quartz Syenite

QuartzSyenite

QuartzMonzonite

Quartz

Monzodiorite

Syenite Monzonite Monzodiorite

(Foid)-bearingSyenite

5

10 5 65

!Foid"-#earin$Monzonite

(Foid)-bearingMonzodiorite

90

Alkali Fs.

Syenite

!Foid"-#earin$Alkali Fs. Syenite

10

!Foid"Monzosyenite

!Foid"S

yenite

!Foid"Monzodiorite

!Foid"G

a##ro

Qtz. %iorite&Qtz. Ga##ro

5

10

%iorite&Ga##ro&Anorthosite

!Foid"-#earin$%iorite&Ga##ro

60

!Foid"olites

Quartzolite

Granite Grano-diorite

'onalite

Alk

ali

Feld

sparG

ranite

Q !Quartz"

A !Alkali-

(elds)ar *

!*la$ioclase"

F !Felds)athoids"

60

'he rock +ust

contain at least

10, o( thesu+ o(

the +inerals on the

corners.

(he prefi $"oid refers to feldspathoid, a

)ariety of generally low8silica felsicminerals lie nepheline! ;/ &. (=M? &t is meant to 3e replaced

3y the actal feldspathoid present, so a

nepheline83earing mon#odiorite wold

3e called a nepheline mon#odiorite!


5/11

6lassification of mafic and ltramafic igneos rocs

&45. classification schemes for coarse8

grained ga33roic rocs $left and ltramafic

rocs $3elow!


6/11

6lassification of )olcanic rocs: P"

&45. classification scheme for )olcanic

rocs! (his wors the same way as for

the &45. scheme for pltonic rocs, 3thistorically )olcanic roc names ha)e

3een different and fewer!

Yo might wonder how it is possi3le to

9antify all of the minerals in a )olcanicroc, gi)en that mineral grains in many

)olcanics are )ery small and many

)olcanics contain a lot of glass!

&n sch cases 9antification of theidentifia3le crystals is meaningless in

the sense of this diagram! &t is more

sefl to plot a )olme norm from a

chemical analysis instead!

!(oid"-#earin$ 'rachyte

!(oid"-#earin$ atite

!(oid"-#earin$Andesite&asalt

!Foid"ites

10

60 60

5 65

10

20 20

60 60

! P

"

3hyolite %acite

'rachyte atite Andesite&asalt

*honolite 'e)hrite

4o

olcanic

rocks

!Foid" !Foid"


7/11

6lassification of )olcanic rocs: fragmental tetres6lassification schemes for the pyroclastic rocs! Aeft, 3ased on the type of

material $after PettiBohn, 1C7@! ight, 3ased on the si#e of the )olcanic

fragments $after "isher, 1CDD!


8/11

6hemical classification of igneos rocs:


9/11

6hemical classification of igneos rocs: E8.i


10/11

6hemical classification of igneos rocs: .i8Zr8(i

&nterestingly, certain trace elements )ary more or less with the maBor

elements that define roc mineralogy! ;ata from the Partridge "ormation

)olcanics, Massachsetts $>ollocher, 1CC'!


11/11

6hemical

classificationof igneos

rocs:

igneous classification

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