Geology Reference
In-Depth Information
Fig. 6.7 Phase relation in the
diopside
-
nepheline system
under 2.8 GPa (after Singh
et al. 2000)
170
1700
1600
X
1500
L
Ne
+
ss
1400
Di +L
ss
L
E
1300
Di +Ne +L
ss
ss
1200
Di +Ne
ss
ss
1100
1000
2
20
30
40
50
60
70
80
90
100
Nepheline
(NaAlSiO
4
Diopsid
(Weight percent)
(CaMgSi O )
2
6
Fig. 6.8 Phase relation in the
diopside
1300
126
nepheline system in
presence of H
2
O at 1.0 GPa
(after Singh et al. 2000)
-
1200
Di
+L+V
ss
11 00
L+V
Di
+Amph+L+V
1000
ss
900
800
700
600
Di +Amph+Ne
+V
ss
ss
Ne +Di
+L+V
ss
ss
500
0 0 0 0 0 0 0 0 0 0 0
Diopside
Nepheline
(NaAlSiO
4
(Weight percent)
(CaMgSi O )
26
nepheline
ss
+ diopside
ss
+ amphibole. Melilite and olivine, which appear as a
reaction product of diopside and nepheline at atmospheric pressure are absent.
Singh et al. (2000) studied a composition Di
40
Ne
60
in presence of excess water
pressure (Fig.
6.9
). They fused this starting material to glass and crystallized it at
800
C. The crystalline material contained diopside
ss
, melilite and nepheline. Their
results are summarized in Fig.
6.9
. The line A
°
C denotes the solidus for the
studied composition. Reference to the study of the join under atmospheric pressure
(Schairer et al. 1962) suggests that there is a drastic decrease in the solidus from
1,100
B
-
-
C. Above 0.3 GPa there is no
change in the temperature of the solidus and it is essentially constant at 700
°
at 1 bar to 750
°
C at 0.17 GPa, a drop of 350
°
°
C.
Above the line D
E, melilite and forsterite
ss
completely disappear. Below the curve
-
B
C, forsterite reacts with the liquid and is eliminated. The curve F
G marks the
-
-
disappearance of amphibole at higher temperatures. The curve I
H
J marks the
-
-
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