Geoscience Reference
In-Depth Information
Table 7.14 Early Hydrothermal Synthesis of Various Dense
Anhydrous Aluminosilicates
[128]
Temperature (
C)
Silicate
Starting Material
Pressure
1
20,000 kg/cm
4
Jadeite
Sodium sulfate, kaolin
1
silica
900
20,000 kg/cm
2
NaCr(SiO
3
)
2
Sodium dichromate
1
silica
900
20,000
30,000
kg/cm2
600
900
Andalusite
Kaolin
1
sodium salts
Kyanite
Alumina
silica
20,000
40,000
kg/cm
2
600
900
1
Sillimanite
Kaolin
1
fluorides
20,000
30,000
kg/cm
2
600
900
Topaz
Kaolin
1
fluorides, but
higher fluoride contents
or kaoline
1
NH
4
HF
2
20,000 kg/cm
2
Epidote and zoisite
hydrated calcium and
iron nitrates, hydrated
alumina and silica
800
Garnet
Grossularite
15,000 kg/cm
2
600
800
20,000 kg/cm
2
Andradite
600
800
20,000 kg/cm
2
Almandine
600
900
30,000 kg/cm
2
Pyrope
900
30,000 kg/cm
2
Mg
3
Fe
2
(SiO
4
)
3
900
20,000 kg/cm
2
Mn
3
Fe
2
(SiO
4
)3
800
20,000 kg/cm
2
Fe
3
Fe
2
(SiO
4
)3
800
20,000 kg/cm
2
Mg
3
Cr
2
(SiO
4
)3
800
7.9.1 Bismuth Silicate
Bismuth silicate, Bi
12
SiO
20
(BSO), is of considerable interest for optical signal pro-
cessing. It is popular as a photorefracting crystal. The photorefractive effect can be
described as a combination of the photoconductive and the electro-optic effects
used in a variety of applications like nonlinear mixing including active spatial filter-
ing phase conjugation by way of degenerating four-wave mixing optical processing
devices such as optical oscillators, and as a technique useful for nondestructive mate-
rials analysis. Litvin
[129]
has studied the system Na
2
O
a
Bi
2
O
3
a
SiO
2
a
H
2
Ounder
450
C, P
5
hydrothermal conditions: T
5
350
400
500 atm in NaOH solution up
to 40 wt%.
Figure 7.26
shows the fields of crystallization of BSOs in the system
Na
2
O
-Bi
2
O
3
(bismite), Bi
2
SiO
20
(sillenite), and Bi
4
Si
3
O
12
(eulytite). Bi
2
SiO
20
crystallizes under
hydrothermal conditions in NaOH (1
a
Bi
2
O
3
a
SiO
2
a
H
2
O. The following phases have been obtained:
α
40 wt%) solutions
and 350 atm pressure
[130]
. Whereas eulytite crystallizes with NaOH (21 wt%),
and it does not depend on the ratio of the starting components (Bi
2
O
3
1
60 wt%) and KOH (1
SiO
2
). It