Geology Reference
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Fig. 11.5 Phase relation in
the join Ak
60
Ab
40
-Lc
60
Ab
40
-
(SiO
2
)
60
Ab
40
at 1 atm (after
Gupta and Gupta 1997)
Ak
Ab
60
40
1260
12
1
2
C
Diopside
SS
13
3
8
5
4
6
11
7
1160
1110
9
(K, Na) Feldspar
Leucite
Trid
ymite
1110
D
Lc
Ab
(SiO ) Ab
260
60
40
40
(1) One at Lc
20
Ak
17
Q
38
Ab
25
(Di
ss
+K
-
Na Felds + Tri + L) and 1,135
±
5
°
C, and
(2)
the other at Lc
44
Ak
15
Q
16
Ab
25
(Lc
ss
+K
Na Felds + Di
ss
+ L) and
-
1,132
±
5
°
C.
Figure
11.5
shows that 40 wt% albite join cuts the phase volumes of leucite
ss
,
(K
Na) feldspar, diopside
ss
and tridymite. Two piercing points also occur in this
join at
-
(1) Lc
13
Ak
11.5
Q
35.5
Ab
40
(Di
ss
+K
Na Felds + Tri + L) and 1,085
°
C, and
-
(2) Lc
41
Ak
15.5
Q
3.5
Ab
40
(Lc
ss
+K
Na Felds + Di
ss
+ L) and 1,139
°
C.
-
11.3 Petrological Signi
cance of the System
Leucite-Akermanite-Albite-SiO
2
If a small amount of possible alumina present in diopside (as Ca-Tschermak
s
molecule) and melilite (as gehlenite molecule), respectively, are ignored, the system
leucite-akermanite-SiO
2
(Fig.
11.2
) may be treated as ternary and the points G, H
and K may be considered to have been formed by the intersection of three uni-
variant lines and the akermanite-leucite-SiO
2
plane. The subsolidus phase relations
in the join Lc
75
Ab
25
-Ak
75
Ab
25
-Q
75
Ab
25
and Lc
60
Ab
40
-Ak
60
Ab
40
-Q
60
Ab
40
are
summarized in Figs.
11.6
and
11.7
, respectively. The course of crystallisation of
liquids in this system is shown in Fig.
11.8
. Final assemblages in the system leucite-
akermanite-SiO
2
are controlled by the joins Lc-(Di + Wo) and Sa-(Di + Wo). The
invariant assemblages in different sections of the system are summarized in
Fig.
11.3
. It is also re
'
flowsheet diagram (Fig.
11.8
). Although wol-
lastonite
ss
is one of the critical phases controlling subsolidus phase assemblages in
ected in the
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