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Clay - Geology

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An Introduction to Clay Geology

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Clay is a fine-grained natural material of soil and contains many clay minerals. The size of the soil particles of clay is usually less than 0.005 mm. There are also rocks that are composed of clay particles. The rock here means a composition of soils, ceramic clays, clay shales, mudstones, glacial clays, and deep-sea clays. Characterised by the presence of clay minerals in varying amounts of organic and detrital materials, such as quartz, the clay geology is formed. The clay geology is also defined by plasticity which is developed when there is a molecular film surrounding the clay particles making it flexible and when in dried form it becomes hard and brittle and non-plastic. Most of the clay is formed as the result of weathering.


Features of Clay Geology

As mentioned above, the defining characteristic of clay is the plasticity when it is wet and the hard nature in dried form. Clay geology shows a huge variety and broad range of water content holding in between the minimum when it moist enough to be moulded and the maximum when the moulded clay is just dry enough for holding on to a shape. For example, the plasticity limit of kaolinite clay, from the kaolinite geology, ranges from about 36% to 40% and the liquid limit ranges between 58% and 72%.


The characteristics of the plasticity of clay geology are attributed to the mineral content such as hydrous aluminium phyllosilicate minerals. There are thin plates formed by interconnecting oxygen and hydroxyl ions which are part of the mineral content. These plates are tough and flexible thus providing the inherent characteristics of the clay. 


The chemistry of the clay minerals and their ability to retain nutritional content such as the cations like potassium and ammonium are important for soil fertility. Some clay minerals are known as the swelling clay minerals as they can take up water to great extent. They increase in volume with the absorption of water and when dried they shrink back to their original volume which can produce cracks and other distinctive textures such as “popcorn” texture in clay deposits. Examples include clay from the smectite geology site and bentonite geology site which is also known as the blue clay. Especially, the clay from the bentonite geology (or blue clay geology) isn't favourable for civil engineering projects because of this property. 


Varieties of Clay Geology

The main kinds of clays are obtained from the kaolinite geology, montmorillonite-smectite geology, illite geology and bentonite geology (or blue clay geology). There are a wide variety of clays, approximately, 30 different types of “pure” clays with a variety of mineral content. But the most naturally available clay deposits consist of the different types of clay along with other weathered minerals. The easiest way to identify clay minerals is X-ray diffraction rather than any other chemical or physical tests. Another kind of clay geology from which a type of clay is obtained is the fire clay geology. The fire clay geology, from which the fire clay is obtained, consists of mineral aggregates of hydrous silicates of aluminium with the presence or absence of free silica. 


Chlorite, vermiculite, talc and pyrophyllite are the types of minerals obtained from metamorphic rocks. The particles of such clay metamorphic rocks are very high in nutritional value and thus provide a significant amount of nutrition nurturing life. Thus, the plant life throws on the mineral content derived from the clay metamorphic rocks. 


Concluding with the Importance of Clay

Clay is one of the most important of the various soil components. It has a wide variety of usage and essential material in various industries. As a component of the soil, they are responsible for providing the plants with the environment for growth and by extension nearly all life on the surface of the Earth. Their porous nature aids them in providing aeration, and in water retention. Clay is also a reservoir of nutrient material such as potassium oxide, calcium oxide, and nitrogen as well. 


Furthermore, they are used in pottery. This culture of pottery making surpasses many centuries of human history. Clay pottery also serves as a record of past civilizations. They are used as building materials in bricks either in baked form or even in raw form for ages. Fire clay is another type of clay that is used for the manufacture of ceramics such as fire brick which is used for making furnaces, fireplace, kilns, fireboxes, etc.


Along with bricks clay is also used for making tiles, the cruder types of pottery, as china clay or kaolin for the finer grades of ceramic materials. Another major usage of the china clay is paper coating and filler giving the paper a glossy appearance and increases the opacity of the paper. It is also used in refractory materials including fire brick, chemical ware, and melting pots for glass and also in heat insulators as it increases the resistance to heat. Wool scouring is another example of usage of a certain type of clay known as fuller’s earth. In the process of rubber compounding, the addition of clay increases the resistance for wear and eliminates the moulding troubles. 


Even in engineering, clay materials serve vital purposes. In the construction of the dams, clay provides water impermeability characteristic when added with porous soil. It serves the same purpose of controlling water loss in canals. Along with the limestone, clay either in pure or impure form is utilized as the raw material of portland cement. After treating it with acid, clay can be used as a water softener. Clay also helps in removing calcium and magnesium from the solution and substitutes sodium. One of the other major usages of clay is drilling mud i.e. heavy suspension consisting of chemical additives and weighting materials when employed in rotary drilling. 

FAQ (Frequently Asked Questions)

1. What is Clay and How is it Formed?

Ans: Clay is a type of soil. It is a mixture of particles from weathered minerals from rocks. These rocks are usually in contact with water, air, or stream. It is fine-grained with particles of a size less than 0.005 mm diameter. As mentioned above, the rocks are weathered by a natural force such as wind and water which include boulders on a hillside, sediments on sea or lake bottoms, and rocks in contact with water heated by magma. 

2. Is Clay Rock or Mineral?

Ans: Clay is a fine-grained minute soil particle with diameters below 0.005 mm. It is formed of component minerals that have been weathered over time by natural weathering of sedimentary rocks containing minerals. Thus, clay is neither a rock nor a mineral, as it is a soil-type composed of many mineral particles.