How to Plot Ternary Diagrams

8/11/2019 How to Plot Ternary Diagrams

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How to plot ternary diagrams


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Ternary diagrams

Used to represent three variables

Very useful for geochemical and petrological

data

Often used as a means of classifying data and

rocks


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Ternary Diagrams

Suppose we have a hypothetical rock with the following

hypothetical minerals:

P 23.2%Q 25.2%

X 36%

Y 10.4%

Z 5.2%

Total 100%

Now suppose we want torepresent this rock just in terms

of the minerals X, Y & Z

How would we do this?


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Ternary Diagrams

First, we would have to normaliseour data to

just these three variables:

P 23.2%

Q 25.2%

X 36%

Y 10.4%

Z 5.2%

Total 100%

X 36

Y 10.4

Z 5.2

Total 51.6

So, we multiply each

by 100/51.6 = 1.94

X 70

Y 20

Z 10

Total 100

x 1.94 =


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Ternary

There are two methods for plotting this data

on a ternary diagram..


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Ternary Diagrams

Method 1

Use when ternary diagram

has grid lines

Each apex represents 100%of that component

The horizontal lines opposite

each apex

Count up from 0% for eachcomponent

E.G. 1,A 40 %

B 50 %

C 10 %


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Ternary Diagrams

Method 1


has grid lines



each apex


E.G. 2,X 70 %

Y 20 %

Z 10 %


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Ternary Diagrams

Method 1


has grid lines



each apex


E.G. 2,X 70 %

Y 20 %

Z 10 %


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Ternary Diagrams

Method 2Use when ternary diagram hasno grid lines (manyclassification diagrams)

Ratio the two smallestcomponents (100Y/(Y+Z)).Here, this equals 2000/30 =67%

This Y/Z ratio will remain thesame regardless of X. So draw a

line from the X apex to a Y:Zratio of 67% and plot where itcrosses the 70% X position

E.G. 2,X 70 %

Y 20 %

Z 10 %


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Ternary Diagrams - examples

We have a course-grained (plutonic)igneous rock with the followingmineral proportions:

Hornblende 10.4%

Pyroxene 5.2%

Quartz 29.8%

Alkali Feldspar 10.4%

Plagioclase Feldspar 44.2%


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This particular classification diagramrequires that Quartz (Q), Alkali-feldspar (A) and Plagioclase Feldspar(P) make up a total >10%

Hornblende 10.4%

Pyroxene 5.2%Quartz (Q) 29.8%

Alkali Feldspar (A) 10.4%

Plagioclase Feldspar (P) 44.2%


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This particular classification diagramrequires that Quartz (Q), Alkali-feldspar (A) and Plagioclase Feldspar(P) make up a total >10%

Hornblende 10.4%

Pyroxene 5.2%Quartz (Q) 29.8%

Alkali Feldspar (A) 10.4%

Plagioclase Feldspar (P) 44.2%

Now, how do we plot this data on

our ternary (classification)

diagram?


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First, normaliseour data to just these three

variables:

Hbl 10.4%

Pyx 5.2%

Q 29.8 %

A 10.4%

P 44.2%

Total 100%

Q 29.8

A 10.4

P 44.2

Total 84.4

So, we multiply each

by 100/84.4 = 1.18

Q 35.2 %

A 12.3 %

P 52.5 %

Total 100

x 1.18 =


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Q 35.2 %

A 12.3 %

P 52.5 %

Total 100 %

Q/A ratio = 100x35.2/(35.2+12.3)

= 74.1 %

GRANODIORITE

52.5% P74.1% Q/A

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How to Plot Ternary Diagrams