includes non-crystalline inorganic constituents, such as volcanic glasses. Volcanic
glasses and apatite are introduced in Chap. 4 and Sect. 6.3, respectively.
Particles larger than silt includes fine rock fragments, complex particles of
different minerals, and partially weathered minerals. After introducing the major
primary minerals in soils, this chapter exemplifies the mineral composition of fine
rock fragments on a polished section, and partially weathered minerals.
2.2 Average Mineral Composition of the Earth’s Crust
Earth’s surface is naturally mobile. The mobile layer is made up of plates comprising
the Earth’s crust and uppermost mantle. On average, the Earth’s crust is 40 km thick
on continents and 6 km thick in the oceans. The upper mantle consists mainly of
peridotite, whereas the crust consists of igneous rocks, sedimentary rocks, and
metamorphic rocks (Fig. 2.1). These three rock families of the Earth’s crust can
interchange through diastrophism (the rock cycle, Fig. 2.2) (Skinner and Mruck
2011). The phases of the rock cycle can undertake various shortcuts. The rock cycle
is active in the subduction zone of a plate and in the collision zones of continents, but
it is relatively inactive in stable continental crust. However, on the surface of the
continental crust, soil formation processes are continuously active.
According to the estimated average element composition of the Earth’s crust,
oxygen is the most abundant element, followed by Si and Al (see Fig. 2.1). The crust
consists of 65% igneous rocks, 27% metamorphic rocks, and 8% sedimentary rocks
(Fig. 2.1). Approximately two-thirds of the igneous rocks are basic rocks; neutral
and acidic rocks constitute approximately one-sixth each. The very surface of the
Earth’s crust is dominated by sedimentary rocks, which are strongly affected by
weathering, erosion, transportation, and deposition (Fig. 2.2).
The rocks of the Earth’s crust are dominated by plagioclase, followed by quartz,
alkali feldspar, and other silicates. Collectively, these minerals constitute approximately 92% of the rock material (Fig. 2.1). Other minerals are non-silicate minerals
such as carbonates, sulfates, phosphates, sulfides, fluorides, and chlorides. The
alteration of rocks and minerals depends on the soil formation factors, which vary
across the surface of the Earth.
2.3 Silicate and Silica Minerals
2.3.1 Grouping of Silicate and Silica Minerals
Silicate and silica minerals are grouped into six types based on the bonding structure
of their silicate tetrahedrons. Examples and the ideal chemical formulas of the six
types of silicates are summarized in Table 2.1. The model structures of five silicate
types are shown in Fig. 2.3. Nesosilicates are characterized by single SiO 4 tetrahedra
12
2 Primary Minerals
glasses and apatite are introduced in Chap. 4 and Sect. 6.3, respectively.
Particles larger than silt includes fine rock fragments, complex particles of
different minerals, and partially weathered minerals. After introducing the major
primary minerals in soils, this chapter exemplifies the mineral composition of fine
rock fragments on a polished section, and partially weathered minerals.
2.2 Average Mineral Composition of the Earth’s Crust
Earth’s surface is naturally mobile. The mobile layer is made up of plates comprising
the Earth’s crust and uppermost mantle. On average, the Earth’s crust is 40 km thick
on continents and 6 km thick in the oceans. The upper mantle consists mainly of
peridotite, whereas the crust consists of igneous rocks, sedimentary rocks, and
metamorphic rocks (Fig. 2.1). These three rock families of the Earth’s crust can
interchange through diastrophism (the rock cycle, Fig. 2.2) (Skinner and Mruck
2011). The phases of the rock cycle can undertake various shortcuts. The rock cycle
is active in the subduction zone of a plate and in the collision zones of continents, but
it is relatively inactive in stable continental crust. However, on the surface of the
continental crust, soil formation processes are continuously active.
According to the estimated average element composition of the Earth’s crust,
oxygen is the most abundant element, followed by Si and Al (see Fig. 2.1). The crust
consists of 65% igneous rocks, 27% metamorphic rocks, and 8% sedimentary rocks
(Fig. 2.1). Approximately two-thirds of the igneous rocks are basic rocks; neutral
and acidic rocks constitute approximately one-sixth each. The very surface of the
Earth’s crust is dominated by sedimentary rocks, which are strongly affected by
weathering, erosion, transportation, and deposition (Fig. 2.2).
The rocks of the Earth’s crust are dominated by plagioclase, followed by quartz,
alkali feldspar, and other silicates. Collectively, these minerals constitute approximately 92% of the rock material (Fig. 2.1). Other minerals are non-silicate minerals
such as carbonates, sulfates, phosphates, sulfides, fluorides, and chlorides. The
alteration of rocks and minerals depends on the soil formation factors, which vary
across the surface of the Earth.
2.3 Silicate and Silica Minerals
2.3.1 Grouping of Silicate and Silica Minerals
Silicate and silica minerals are grouped into six types based on the bonding structure
of their silicate tetrahedrons. Examples and the ideal chemical formulas of the six
types of silicates are summarized in Table 2.1. The model structures of five silicate
types are shown in Fig. 2.3. Nesosilicates are characterized by single SiO 4 tetrahedra
12
2 Primary Minerals