Geoscience Reference
In-Depth Information
1600 °
M
1500 °
Melt
T
T 2
M 2
1400
°
X 2
X 1
Anorthite + melt
Diopside + melt
M 3
1300 °
T 3
T 4
1200 °
Diopside + anorthite
R
CaAl 2 Si 2 O 8
Anorthite
CaMgSi 2 O 6
Diopside
20
30
40
50
wt%
60
70
80
90
Figure 7.24 Equilibrium diagram of the system diopside anorthite at pressure 1 bar [108] .
this, Morey [109] , published a systematic investigation of the ternary system
H 2 O
SiO 2 . Here, for the first time, studies were carried out in a system-
atic fashion with the temperature carefully controlled and measured and the pres-
sure held constant throughout the experiment. Figure 2.6 shows the isothermal
polybaric saturation curves and the isobaric polythermal saturation curve at 1 atm
pressure of H 2 O vapor. This marked the beginning of the phase equilibria studies
in the silicate system and, followed by this, several other important publications
came out especially from the Geophysical Laboratory in Washington, pertaining to
the silicate systems. In fact, Bowen [110] developed his famous petrologic ideas
based on these phase equilibrium data. One of the most important phase equilib-
rium data among the silicate systems is for the system MgO
a
K 2 SiO 3 a
H 2 O given by
Bowen and Tuttle [111] . This work, in many respects, laid the foundation for much
of the subsequent work on silicate systems. In this work, the authors describe the
change of assemblages with temperature and also show the effect of pressure on
the temperatures involved. Figure 7.25 shows the pressure
a
SiO 2 a
temperature curves of
univariant equilibrium in the system MgO
115] . There are quite
a large number of such silicate systems reported in the literature, contributing to
the understanding of complex geological processes. Some of the systems like
Al 2 O 3 a
a
SiO 2 a
H 2 O [112
SiO 2 a
H 2 O [116
118] , CaO
a
SiO 2 a
H 2 O [119
122] , SrO
a
SiO 2 a
H 2 O
[123] , MgO
a
Al 2 O 5 a
SiO 2 a
H 2 O [112
115] ,
and alkali
a
Al 2 O 3 a
SiO 2 a
H 2 O
[124
127] are noteworthy to mention here, as they provide a vast amount of
information on the understanding of the natural geological processes leading to
the formation of various rocks and minerals.
We give here some of the earliest works on the synthesis of various silicates in
general, before going into the systematic synthesis of selected silicates with device
potential, gemstones, and of general interest.
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