Environmental Engineering Reference
In-Depth Information
Figure 9.2.3
Structure of minerals
(a) Tectosilicates: quartz (SiO
2
). SiO
4
tetrahedra are shown in yellow, O atoms in red.
(b) Tectosilicates: albite (Na-feldspar: NaSi
3
AlO
8
). SiO
4
tetrahedra are shown in yellow,
AlO
6
octahedra in pink, O atoms in red, and Na atoms in blue.
(c) Phyllosilicates: kaolinite [Si
4
Al
4
O
10
(OH)
8
]. SiO
4
tetrahedra are shown in yellow, AlO
6
octahedra in pink, O atoms in red, H atoms in white. The sheets are held together by
hydrogen bonding.
(d) Phyllosilicates: smectite [C
x
(Si,Al)
8
(AlFeMg)
4
O
20
(OH)
4
.
nH
2
O, where C is the interlayer
cation that balances the negative structural charge of the clay sheet, in this case
Na
+
. SiO
4
tetrahedra are shown in yellow, AlO
6
octahedra in pink, MgO
6
octahedra
in green, O atoms in red, H atoms in white, Na atoms in blue. As smectites are swell-
ing clay minerals, the interlayer space contains a variable number of water molecules
(in this case, two statistical water monolayers; therefore, the fi gure shows the two-
layer hydrate of Na-smectite).
sediments followed by fi ne sediments are commonly preserved in sedi-
mentary rock sequences.
Figure 9.2.4
illustrates the layered structure of
sediments that are formed by these periodic variations.
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