Soil Minerals | Clay Minerals | Gropus of Clay

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In this article, we will discuss soil minerals.


  1. Introduction  

Soil particles arc composed of minerals. Soil minerals are further divided into primary minerals and secondary minerals. Primary minerals will have the same composition as that parent rock. Sand and gravel, which are the products of mechanical weathering, arc composed of primary minerals. They do not possess cohesion and plasticity characteristics. They are bulky particles and gravitational forces govern their behavior. Secondary minerals occur in silts and clays and are the results of minerals.

Non-clay minerals are amorphous and impart little or no cohesion and weathering. They are further classified as non-clay minerals and clay plasticity al characteristics to the soil. Clay minerals are very tiny crystalline substances.


Soil Minerals


The soil minerals also consists clay mineral which is called as clay minerals


  Clay Minerals  

The three most important groups of clay minerals are montmorillonite, illite, and kaolinite. They are all crystalline hydrous alumino-silicates. The result of studies using the electron microscope and X-ray diffraction techniques show that the clay minerals have a lattice structure in which atoms are arranged in several sheets. The arrangement and chemical composition of these sheets determine the type of clay minerals.

The basic structural units of most clay minerals consist of silica tetrahedrons and an alumina octahedron. Silicon and aluminum may be partially replaced by other elements in these.



  i) Kaolinite  

It consists of alternating silica and alumina sheets, sheets are held together with strong chemical bonds, so kaolinite is a very stable clay. Unlike, other clay minerals, kaolinite does not expand appreciably when wet, so it is used to make pottery. It is also an important ingredient in paper, paint, and other products.
Index Properties of Soil


Read More: Field Identification of Soil


  ii) Montmorillonite  

It is also known as a smectite. It has layers made of two silica sheets and one alumina sheet. The bonding between these layers is very weak, so large quantities of water can easily enter and separate them, thus causing the clay to swell.

This property can be very troublesome or very useful, depending on the situation. Problems with soil expansion include extensive distortions in structures, highways, and other civil engineering projects.

However, this expansive behavior and the low permeability of montmorillonite can be useful for sealing boreholes or providing groundwater barriers. Bentonite, a type of montmorillonite, is commercially mined and sold for such purposes.


Read More: Soil Compaction Numerical


  iii) Illite  

It has layers similar to those in montmorillonite but contains potassium ions between each layer. The chemical bonds in this structure are stronger than those in montmorillonite but weaker than those in kaolinite, so illite expands slightly when wet. Glacial clays in the Great lakes region are primarily comprised of illite.

A number of engineering properties are attributable to the size, shape, surface area, and negative surface charge carried by all clay particles. Two basic types of particle orientations, namely flocculated (edge to face) and dispersed (face to face) are observed in clay minerals.

The net repulsion between particles results in dispersed structures whereas the flocculent structure occurs when there is Diet attraction.



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