Geoscience Reference
In-Depth Information
121
010
120
110
011
111
211
122
100
101
201
221
310
210
320
012
843
411
311
100
401
Figure 7.36 Schematic diagram of the crystal morphology
[182]
.
Figure 7.37 NC diagram of
crystallization in the system
Na
2
O
a
CaO
a
SiO
2
a
H
2
O
[182]
.
μ
SiO
2
Na
2
CaSi
3
O
8
NaCa
2
Si
3
O
8
(OH)
Ca
6
Si
6
O
17
(OH)
2
Ca
5
(SiO
4
)
2
(OH)
2
μ
Na
2
O
a
a
SiO
2
a
Several other compounds crystallize from the system Na
2
O
MO
H
2
O
(where M
Cd, Ca, Ba, and Mn). Among them, the Cd- and Mn-bearing silicates
show interesting physical properties
[175,182,184
5
186]
. Similarly, the Ca-bearing
silicates carry great geological significance and such systems are being studied
extensively
[187
190]
.
Several phases crystallize in the Na
2
O
H
2
O under hydrothermal
conditions.
Figure 7.37
shows the NC diagram of crystallization in the system Na
2
O
a
CaO
a
SiO
2
a
a
CaO
H
2
O. Following are the important phases crystallizing in this system: Ca
[SiO
3
], Ca
6
[Si
6
O
17
](OH)
2
(xonolite), Ca
5
[SiO
4
]
2
3
a
SiO
2
a
(OH)
2
(khondrodite), Ca
6
[Si
4
O
14
]
(kilkhoanite), Ca
8
[Si
5
O
18
] (orthorolite), Ca
6
[SiO
4
][Si
2
O
7
](OH)
2
(dellaite), and so on.
The studies of the crystallization of monocationic calcium silicates reveal that
they are formed in at least two ways:
i. Interaction of soluble silica with calcium compound (through neutralization reaction).
ii. Interaction of aqueous solutions of silica with amorphous or crystalline portlandite.
