Soil Minerals | What are the minerals found in soil?
Soil particle composition plays an important role in the basic understanding Of soil behavior. Soils can be organic or inorganic, depending on their source.
However, Except for the fact that organic soils are a mixture of rotten plant life, skeletons, or small shells Organisms, and soil particles, not much is known about organic soil composition.
Inorganic soils are formed by mechanical or chemical weathering. The inorganic clay particle may be a rock fragment or mineral.
In the present case, the mineral is a chemical element or a compound formed in nature in a geological process, and the stone fragment is a representative of the original rock, which may contain one or more minerals.
Depending on the nature of the atoms, minerals are classified as carbonates, phosphates, oxides, and silicates. Silicate minerals are important to civil engineers.
However, Different systems of atoms in silicate minerals lead to different silicate structures. The most abundant clay minerals are common stone-forming minerals, that is, sheet and framed silicate minerals. These are discussed below.
Clay Minerals
Soil minerals are formed by two basic structural components: tetrahedral and octahedral.
The tetrahedral unit The central silicon atom surrounded by four oxygen atoms is placed at the vertices of the tetrahedron (the basic unit and its symbolic representation are shown in Figure 1.6).
Since Tetrahedrons are composed of hexagonal units called silica sheets.
However, The octahedral unit consists of central ions of aluminum or magnesium surrounded by six hydroxyl ions (the basic unit and its symbolic representation are given in Figure 1.6).
Combining aluminum-oxygen octahedrons gives the gibbsite sheet and magnesium-oxygen Octopods provide a bruise sheet.
Therefore, Considering the valence of atoms in tetrahedral and two octahedral units, it is clear that the units are not electrically neutral and do not exist as single units.
However, the gibbsite and brucite sheets exist because they are electrically neutral.
Sheets can be combined to form two-layer or three-layer sheet minerals or clay minerals.
Watch this to understand the concept of soil minerals:
The original kaolinite component (a two-layer unit) is formed by stacking the gibbsite sheet on the silica sheet.
These components can be stacked on top of each other to form a mineral mesh (Fig. 1.7a).
The bond between the basic kaolinite components is due to hydrogen bonding and secondary valence forces.
Kaolinite minerals are thus very stable and do not allow water to enter the mesh and therefore do not expand when saturated.
However, Kaolinite is the most abundant component of residual soil deposits. Isomorphous substitution (switching from one type of atom to another) is quite common during the formation of sheet silicate minerals.
In kaolinite minerals, the magnitude of isomorphous substitution is negligible. Other clay minerals with two-layer sheets include sarpine (brucite silica sheet composition, Figure 1.7b) and halocyte (similar to kaolinite except for the presence of water between the sheets).
Of the three-layer sheet minerals, montmorillonite and elite clay minerals are the most common.
The original three-layer sheet units are formed by placing one silica sheet at the top and one at the bottom of the gibsite sheet.
Figure 1.8a shows the montmorillonite mineral component and lattice. Magnesium or iron isomorphous substitution for aluminum is common in the gibsite sheet.
However, The bond between Through three-layer units Secondary valence forces and interchangeable ion contact. The bonding of these sheets is very weak and water can enter between the components.
The mineral has a significant affinity with water and absorbs large amounts of water, causing swelling.
Similarly, there is shrinkage in dry weather. Most Indian black cotton soils contain this mineral and care must be taken to design structures in such soil.
Illite consists of basic montmorillonite units but is bound by secondary valence bonds and potassium ions (K +) as shown in Figure 1.8b.
However, Aluminum is replaced by silicon in the gibbsite sheet by about 20% due to isomorphous substitution.
The mineral is very stable and does not swell or shrink, unlike montmorillonite.
Since The basic constituents of clay particles are sheet structures, the particle formed by stacking such base units ends up with a plate shape.
The surface area of clay particles per unit mass is usually called the specific surface.
However, The clays with the smallest particles have the largest surface area. The surface area of kaolinite is very low Compared to montmorillonite.
The specific surfaces of kaolinite, elite, and montmorillonite are about 15, 90, and 800 m2 / g, respectively.
Framework Silicate Minerals
Quartz and feldspar are very common stone-forming minerals, and their frames are abundant in soil.
Move the fractional minerals particlesMaru is equal to the signal due to the nature of their formation.
Therefore, Quartz is one of the minerals that makes it more resistant to weather.
Feldspars can be weathered to form clay minerals. Thus, these minerals sometimes rank in clay and silt-sized particles.
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