# CHapter 7- SYstems with 2 components

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```					Ternary Systems

Winter Chapter 7
C = 3: Ternary Systems:
Example 1: Ternary Eutectic
Di - An - Fo
Anorthite
Note three binary eutectics
No solid solution
Ternary eutectic = M

M

T

Forsterite
Diopside
T - X Projection of Di - An - Fo

Isobaric diagram
illustrating the
liquidus temperatures
in the Di-An-Fo
system at
atmospheric pressure
(0.1 MPa). After
Bowen (1915), A. J.
Sci., and Morse
(1994), Basalts and
Phase Diagrams.
Krieger Publishers.
Crystallization Relationships
Liquid      a
An
An + Liq
Di + Liq

Di + An

Pure Fo forms
Just as in binary
f=?
F=?
f   = 2 (Fo + Liq)
F = 3 - 2 + 1 = 2

If on liquidus, need to specify
only 2 intensive variables
to determine the system
liq
 T and X An or
liq      liq
 X An and X Fo

X of pure Fo is fixed
Lever principle  relative proportions of liquid & Fo
o
 At 1500 C

Liq  x + Fo = bulk a
 x/Fo = a-Fo/x-a
New continuous reaction as liquid follows cotectic:
LiqA  LiqB + Fo + Di
Bulk solid extract
Di/Fo in bulk solid extract using lever principle

1274          M

b

Fo + Liq
1392
Diopside   c          1387
 At1300oC liquid = X
 Imagine triangular plane X - Di - Fo balanced on bulk a

Liq x

a
Di
m          Fo

/              /
Liq total solids = a-m Liq-a

total Di/Fo = m-Fo/Di-m
Partial Melting (remove melt):
Fo - An - SiO2   (at 0.1 MPa)

3 binary systems:
Fo-An eutectic
An-SiO2 eutectic
Fo-SiO2 peritectic

Isobaric diagram
illustrating the cotectic
and peritectic curves in
the system forsterite-
anorthite-silica at 0.1
MPa. After Anderson
(1915) A. J. Sci., and
Irvine (1975) CIW
Yearb. 74.
x
b
a

Fo   1890   En   y
Works the same way as the Fo - En - SiO2 binary

i
k
1557

Fo              En
f

e   b

Fo   En
Diopside-Albite-Anorthite
Isobaric diagram
illustrating the liquidus
temperatures in the
system diopside-
anorthite-albite at
atmospheric pressure
(0.1 MPa). After Morse
(1994), Basalts and
Phase Diagrams.
Krieger Publushers

Di - An Eutectic
Di - Ab Eutectic
Ab - An solid solution
Isobaric diagram
illustrating the liquidus
Isobaric    temperatures in the
system diopside-
polythermal   anorthite-albite at
atmospheric pressure
projection   (0.1 MPa). After Morse
(1994), Basalts and
Phase Diagrams.
Krieger Publishers.
Binary character is usually maintained
when a new component is added

 Eutectic behavior remains eutectic
 Peritectic behavior remains peritectic
 Solid solutions remain so as well

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