Geoscience Reference
In-Depth Information
Discrete 12-membered ring [Si
12
O
36
]. This was observed in the structure of
Na
5
Ce[Si
4
O
12
](
Figure 7.9
)
[66]
. The other ring type [Si
12
O
36
] is found in Ba
5
FeTi
(OH)
4
[Si
6
O
18
]
[67]
. The rings in either structure differ greatly from one another,
e.g., the latter case has higher symmetry and the earlier case has lower symmetry.
Spiral chains [Si
24
O
72
] are found in the structure of Na
3
Y[Si
3
O
9
]. This new type
of infinite spiral formation metachain silicate [Si
12
O
36
] agrees with the formula 12
[SiO
4
]-tetrahedra. Such a matachain silicate is shown in (
Figure 7.10
)
[68]
.
Layers from 6-, 8- and 12-rings [Si
3
O
8
] have been reported in the structure of
K
8
Yb
3
[Si
6
O
15
]
2
(OH) (
Figure 7.11
)
[69]
.
Layers from 4-, 5-, 6-, and 8-membered rings [Si
2
O
5
] was found in the structure
of NaNd[Si
6
O
13
](OH)
2
nH
2
O(
Figure 7.12
)
[70]
. This type of layer forms as a
result of the condensation of the ribbon from the reflection of the 8-membered
rings. Layered radical from [SiO
4
]-tetrahedra with such an arrangement of the rings
is unique among silicate structures.
Layers from 4-, 6-, and 8-membered rings [Si
2
O
5
] was observed in the structure
of K
3
Nd[Si
6
O
15
](
Figure 7.13
)
[71]
. Such an arrangement has been noticed in sev-
eral other rare earth and nonrare earth silicates. Usually the layers are extended and
structures are highly distorted.
Triple columnar [Si
3
O
7
] was demonstrated in the structure of NaR[Si
6
O
14
](
Figure
7.14
)
[72]
. The structure is made up of 3d network from 12-membered complexes.
Figure 7.12 Layers from 4-, 5-, 6-,
and 8-membered rings, [Si
2
O
5
], in the
structure of NaNd[Si
6
O
13
]
(OH)
2
nH
2
O
[70]
.
