Phase Diagrams Continued
n
Liquid
2000
o
Anorthite
p
Two Liquids
1800
T oC
1713
1695
Liquid +
Forsterite
Cristobalite + Liquid
1600
1557
1543
c
Forsterite
+ Enstatite
Enstatite + Cristobalite
M
1470
Enstatite + Tridymite
1400
Mg2SiO4
20
40
MgSiO2
60
80
SiO2
T
Wt.% X2
Forsterite
Updates/questions
- Next week Review and Midterm
Topics: phase diagrams
- 2 component systems:
- Peritectic
- 3 component systems
Solid Solution with Eutectic:
Ab-Or (the alkali feldspars)
Figure 6-16. T-X
phase diagram of the
system albiteorthoclase at 0.2 GPa
H2O pressure. After
Bowen and Tuttle
(1950). J. Geology.
Effect of PH O on Ab-Or
2
Figure 6-17. The Albite-K-feldspar system at various H2O pressures. (a) and (b) after
Bowen and Tuttle (1950), J. Geol, (c) after Morse (1970) J. Petrol.
Binary Peritectic Systems
Liquid
2000
a
Two Liquids
1800
T oC
1713
1695
Liquid +
Forsterite
b
Cristobalite + Liquid
1600
1557
1543
Enstatite + Cristobalite
Forsterite
+ Enstatite
e
1470
Enstatite + Tridymite
1400
20
Mg2SiO4
Forsterite
40
MgSiO2
Enstatite
60
Wt.% X2
80
SiO2
Figure 6-12. Isobaric T-X phase
diagram of the system Fo-Silica at
0.1 MPa. After Bowen and Anderson
(1914) and Grieg (1927). Amer. J.
Sci.
The Peritectic 1: X between Fo-En
1557
im
k
d
Fo
En
Bulk X
c
The Peritectic 2: X between En-Cr
x
i
m
k
y
1557
1543
d
c
bulk X
Fo
En
Cr
Incongruent Melting of Enstatite
i
1557
d
1543
c
bulk X
Fo
En
Cr
Ternary Systems
C = 3: Ternary Systems:
Example 1: Ternary Eutectic
Di - An - Fo
Anorthite
M
T
Forsterite
Diopside
Crystallization Relationships
Liquid
a
Fo + Liq
Di + Liq
Di + Fo
An
Pure Fo forms
Just as in binary
f=? F=?
Ternary lever w/ 3 phases
 Imagine
triangular plane X - Di - Fo balanced on bulk a
Liq x
a
Di
m
/
/
total Di/Fo = m-Fo/Di-m
Liq total solids = a-m Liq-a
Fo
Pressure Effects