with no Si–O–Si bonding. Other silicates are constructed from units of two or more
connected SiO 4 tetrahedra. Sorosilicates are dimers of SiO 4 tetrahedra.
Cyclosilicates have a ring structure composed of 3–6 SiO 4 tetrahedra. Inosilicates
Mineral
Rock
Element
0
2 0
4 0
6 0
8 0
1 0 0
Composition %
O
Si
Al
Fe
Mg Ca Na K Others
46.6
27.7
8.1 5.0
3.6 2.8 2.6 2.1 1.9
Felsic Intermediate Ultramafic
Mafic
10.4
11.6
42.5
0.2
27.4
7.9
Plagioclase
Quartz
Alkali feldspar
Pyroxenes
Micas
Amphiboles
Olivines
Clay minerals
Others
39
12
12
11 5 5
3 4.6 8.4
Metamorphic Sedimentary
Igneous
Fig. 2.1 Average element and rock and mineral (Wyllie 1971) compositions of the Earth’s crust
Igneous rocks
Weathering
Soil formation
Soil formation
Aeolian dust
Magma
Transportation
Oceanic crust
Continental
crust
Metamorphic rocks
Sedimentary rocks
Fig. 2.2 Schematic of the rock cycle. Various shortcuts are possible in this cycle
2.3 Silicate and Silica Minerals
13