Factors such as parental material and biological formers as well as physical and chemical agents such as exfoliation and cation exchange give rise to soils and minerals.
Identifying the structure of the soils, especially their mineralogical composition, is fundamental since it controls the shape, size, properties and behavior of the soils.
formation-mineralogy-soilsIn the formation of clay minerals, inheritance, neoformation and transformation mechanisms intervene, as well as their structure and atomic bonds provide us with information about the clay mineral group and its properties. Within the chemical interaction between soil and water, the Diffuse Double Layer theory explains the mechanisms by which water molecules are attracted to the surface of the clay particle. To know how the soil is formed, it is necessary to understand the influence of sediment transport, erosion and deposition, as well as its post-depositional changes, therefore, we will delve into these concepts and the physical and chemical changes that occur during the conversion of sediment into rock. sedimentary.
Keywords- atom, cycle, diagenesis, dipole, bond, structure, mineral, rock, sediment, and soil.
1. Introduction
What motivated this article is to delve into how the soil and its minerals originated and formed since this helps us to develop engineering applications for the benefit of humanity, understanding as soil the agglomeration of mineral aggregates that can be divided by processes mechanical or water. For geotechnical engineers, it is essential to understand the soil, that is, to know what its properties are since it is essential for the design and construction of a civil work and without this understanding we would be full of insecurity and uncertainty about the risks and circumstances that affect the structures, therefore, a good visual inspection, collection of weather information,seismic and geological as well as laboratory tests lead us to the development of a soil study that gives us security about our work and translates into an efficient and economical design.
The objectives are to know the agents and factors that give rise to soils and minerals, to understand how the atomic structure of the minerals that make up the soil affects their properties and to deepen the theory of the double diffuse layer on the soil-water interaction.
In general, the article deals with which are the agents that affect both physically and chemically in the evolution of the soil, their properties are analyzed individually and collectively in addition to their geological characteristics. It is important to understand the mechanisms of mineral formation and how their atomic structure alters their properties. The theory of the diffuse double layer will be addressed, which explains how the chemical interaction between water and soil occurs. To know how the soil was formed and its properties, it is necessary to take into account the processes of erosion, transport and deposition. Finally, it will be analyzed how the transformation of clay mineral into rock and soil occurs through a set of processes known as diagenesis.
Structure:
- Behavior, Geology and Formation of Soils Evolution of Clay Minerals Structure and Types of Atomic Bonds in Minerals Water-Soil Chemical Interaction Diffuse Double Layer Theory Erosion, Transport and Deposition Post Depositional Changes in Sediments: Diagenesis
2. Main Body
2.1. Behavior, Geology and Formation of Soils
2.1.1 Behavior
To analyze how the soil acts, it is necessary to analyze it individually and collectively. The main characteristics individually are shape and size, and if we refer specifically to clays, it would be the mineralogical composition. Collectively, the set of particles presents main characteristics such as relative density if it is a non-cohesive soil and consistency if it is cohesive.
The origin of the soils due to physical-chemical weathering of the rocks can be residual or transported, a residual soil is that material from the rock that has not been transported from its initial location and preserves the weakness planes of the rock within delimited depths, a soil is considered transported if it is the product of the action of transport factors that operate on the rock or the original soil, among these we have volcanoes, rivers, wind and glaciers, producing wind, alluvial and glacial deposits. Soils can also originate through the decomposition of organic matter, these are created on site due to the grouping of solid skeletons or pieces of animals.
2.1.2 Geology
Geologically the earth is divided into crust, mantle (upper and lower), core (inner and outer) and its approximate radius measured at the equator is 6400 km. An important geological property is the geothermal gradient, which is defined as the increase in temperature with depth. The larger the geothermal gradient, the magma will increase its solidification speed and produce tiny crystalline structures due to the lack of time for the atoms to react. The earth is made up of different elements, the most abundant of which are oxygen, silicon, aluminum and iron "Figure 1".
Figure 1. Composition of the earth
Source: Mitchell and Soga (2005)
The geological cycle is a continuous process of transformation that began billions of years ago and consists of four phases that are removal, deposition, sediment formation and movements of the crust "Figure 2"
Figure 2. Simplified geological cycle Source: Mitchell and Soga (2005)
2.1.3 Training
It is important to mention that rocks, like soils, are made up of small crystalline units known as minerals. A mineral with a complicated structure to break forms a coarse-grained (stable) soil, but another mineral with an easy-to-break structure forms fine-grained (more unstable) soils.
Among the main factors that influence the formation of soils are:
- The matter that gave rise to the soil, be it igneous, sedimentary or metamorphic rock The water that produces physicochemical reactions and induces the hydrolysis and carbonation process The relief since water also acts on the topography of the region The climate because it determines the color of the soil The temperature because the relationship between the amount of clay in a soil and the temperature is directly proportional The human being as it builds and alters natural conditions The main agents that act on the formation of soils They are divided into two groups: Physical alterations that produce the decomposition of the particles without changing their original composition, for example: erosion, exfoliation and load relief.Chemical alterations that produce a decrease in particle size and a chemical change in the parent rock, for example: oxidation and cation exchange.
2.2. Evolution of Clay Minerals
Among the processes of formation of clay minerals through weathering we have inheritance, in this the mineral was created by reactions at some stage of the geological cycle and was stable enough to preserve its initial characteristics. Another process is Neo-formation, in this the mineral was formed thanks to reactions between other minerals through solution or chemical weathering and the last formation mechanism is transformation, in this the mineral originated through reactions, but retains some properties initials.
The mineralogical composition of the soil is fundamental as it establishes the shape, size and properties of the particles. Minerals can be classified into primary and secondary, they are considered primary if they retain their authentic crystalline structure, and secondary if they originate through changes between parent minerals.
2.3. Structure and Types of Atomic Bonds of Minerals
It is important to mention that the elemental structure of a large part of minerals are Oxygen-Silica Tetrahedron and Alumine-Hydroxyl Octahedron "Figure 3".
Figure 3. Basic structure of most minerals. Source: Faculty of Agronomy -UBA Lic. Silvana Torri (2015)
Silicates are made up of two elements silicon Si and oxygen O, along with other elements such as aluminum Al, iron Fe and magnesium Mg. Silicates are the base of several minerals formed by a silicon atom tetrahedrally arranged at four oxygen atoms, producing the anion SiO44-.
Clays are formed from the weathering of feldepasts, micas and pyroxenes, in addition they are built from sheets of silica tetrahedron integrating a hexagonal network.
The atomic structure of minerals is formed from primary and secondary bonds, the primary bonds are covalent, ionic and metallic. Covalent bonds occur when two or more atoms exchange electrons from their last orbital level to achieve stability, ionic bonds are caused by electrostatic attraction generated by ions with electrically opposite charges, and metallic bonds are those that are produced by electrostatic attraction. between electrons and cations located in metals and that are free to move. Among the secondary bonds we have the hydrogen bonds product of the attraction of the positive end of a dipole with the negative end of a nearby molecule,potassium bonds are of a chemical type and are given by the union of continuous tetrahedral sheets of clay minerals since potassium K fits into the available hexagon. A type of weak secondary bond is the Van Der Walls Force, this is formed by attraction and repulsion of induced dipoles or molecules.
Structure of some clay minerals:
- Kaolinite: laminar form of greater thickness, consists of continuous layers of elemental sheets of Gibbsite Silica. 1: 1 configuration and baseline separation of 7.2 Å (Å is the unit of measure equivalent to one millionth of a millimeter) “Figure 4”.
Figure 4. Mineral formation - Kaolinite
Source: Barrios, Deeyvid Oscar Sáez. 2017. Origin and Formation of Soils.
- Illite: laminar form, consisting of a Gibbsite sheet linked with two Silica sheets. 2: 1 configuration and 10 Å basal spacing "Figure 5".
Figure 5. Mineral formation - Illite
Source: Barrios, Deeyvid Oscar Sáez. 2017. Origin and Formation of Soils.
- Montmorillonite (smectite): laminar, tubular, elongated form, consisting of a Gibbsite sheet linked with two Silica sheets. 2: 1 configuration and 9.6 Å basal spacing "Figure 6".
Figure 6. Mineral formation - Montmorillonite
Source: Barrios, Deeyvid Oscar Sáez. 2017. Origin and Formation of
Floors
2.4. Water-Soil Chemical Interaction Diffuse Double Layer Theory
For engineering, water is classified into interstitial (pore water) and absorbed water, interstitial water is that which is not affected by inter-particular interactions, while absorbed water is the one that is affected by this type of interactions.
The theory of the double diffuse (ionic) layer refers to the solid-liquid interface and mentions a first layer where the charge is found on the surface of the clay and a second layer that corresponds to the diffuse layer of ions adjacent to the surface. made of clay that neutralizes its negative charges.
Among the forces acting on the diffuse double field we have the electrostatic attraction force which is inversely proportional to the square of the distance between the clay and the cations, the electrostatic repulsion force and the diffusion force which is the one that equals the concentration in all points.
There are several models of the diffuse layer, including Helmholtz's (1879), Gouy-Chapman (1910-1913 and Stern's (1924) models.
- Helmholtz model: a layer of charges on a solid surface and a rigid layer of ions of opposite charge in the solution Gouy-Chapman model: a layer of charges on a solid surface and a diffuse layer of ions with statistical distribution in the Stern's model: a layer of charges on the solid surface and another layer of counterions formed by a rigidly absorbed counter-ion sublayer and a diffuse sublayer of ions in solution.
Figure 7. Diffuse Double Layer
Source: Barrios, Deeyvid Oscar Sáez. 2017. Origin and Formation of Soils.
2.5. Erosion, Transport and Deposition
Erosion is the wear caused on the surface of a body by external agents (such as wind or water) or by the continuous friction of other bodies. Transport is the displacement of eroded materials in a specific place for their subsequent sedimentation in a different material. Sedimentation is the last process of morphogenesis and is based on the accumulation of materials after having been eroded and transported.
Erosion consists of the physical or chemical removal of soils, alluvium, colluvium, sediments or unconsolidated materials. It differs from weathering because it is static, that is, erosion involves transport.
Soil erosion is mainly caused by factors such as water and air currents, particularly in dry land without vegetation, as well as ice, among others. Soil erosion reduces its fertility because it causes the loss of minerals and organic matter "Figure 8".
Figure 8. Comparison of erosion and transport curves for air and water flow. Air is a slightly more effective erosive agent than streams for very small particles, but it is ineffective for particles larger than sands.
Source: Mitchell and Soga (2005)
If the sediment transport occurs by water, it can affect the size of the sediments reducing it by solution, by abrasion in suspended load and by some abrasion and impact in tensile load. Another effect of water is on the shape and roundness since it causes rounding of the sands and gravels, and on the surface texture the water softens and polishes the sands and does not have much effect on the silt. The transport of sediment by air also causes a considerable reduction in particle size, a high degree of roundness and a frosted surface. Transport by ice (glaciers) generates considerable impact and pulverization, angular shapes and damaged surfaces. If transport is by gravity then the effect on size is considerable,the shape it gives to the sediment particles is angular and not spherical, it also produces a damaged surface. Sedimentation consists of grouping eroded and transported materials. The properties of the deposits depend on the origin of the transport agent. For example, if it is through rivers, seas or wind, the material is deposited when the displacement in the medium decreases below the speed of deposition of the load. In the case of ice, deposition originates when it encounters an obstacle or when the mass of ice reaches its maximum extension.seas or wind the material is deposited when the displacement in the medium decreases below the rate of deposition of the load. In the case of ice, deposition originates when it encounters an obstacle or when the mass of ice reaches its maximum extension.seas or wind the material is deposited when the displacement in the medium decreases below the rate of deposition of the load. In the case of ice, deposition originates when it encounters an obstacle or when the mass of ice reaches its maximum extension.
2.6. Post Depositional Sediment Changes: Diagenesis
Diagenesis is a variety of processes that lead sediments to form sedimentary rock. According to the type of sediment, detrital rocks can be formed, that is, those originated from the accumulation of fragments of weathered and eroded rocks or non-detrital rocks can be formed, that is, from substances dissolved in water and made up of remains of organisms.
Possibly there are 3 requirements that must be met for diagenesis in a clay mineral to occur, the first requirement is that there are enough elements such as potassium, magnesium, aluminum and silicon. This can be seen in Arizona specifically in Blue Mesa where the blue Illita "Figure 9" only formed in places where potassium was available.
Figure 9. Clay mineral known as Blue Illite.
Source: Athinarom.gr, 2017
The second requirement is that the combining ion must be accompanied by energy of sufficient intensity to activate the reaction. The energy could be chemical (strong atomic bond), mechanical (high pressure), or thermal (high temperature). The third requirement would be geological time, the passage of a long period of time may not always be necessary, but there are times when it is a characteristic of certain geological systems and could be a special requirement in certain cases.
Clays deposited in a sedimentary environment such as a basin are buried, heated, and gradually enter the diagenetic environment. An important reaction that occurs in shales formed from muds that originally contained Montmorillonite is the gradual conversion of Montmorillonite into mixed Illite-Montmorillonite layers with increasing burial depth and temperature. According to Perry and Hower (1970) an example would be on the Gulf Coast in the United States when the temperature reaches 60ºC. According to Hower, the reaction is generally K-Feldepasts + Montmorillonite à IS + Chlorine + Quartz (1)
3. Conclusions
The origin of soils are rocks and their formation is the product of processes in which the material that makes them up is transformed, that is, weathering. In weathering, the rock undergoes disintegration and decomposition as a result of factors such as water, climate, air or time. Minerals are natural, solid and inorganic substances that have a crystalline structure and are formed as a result of geological processes. Clay minerals are very abundant and form the general matrix of the soil, these minerals can be very varied, for example: Illite, Kaolinite and Montmorillonite, each one is formed in specific climatic conditions and due to their characteristics they give the soil different mechanical properties.
To explain the water-soil interaction, the theory of the diffuse double layer arose, the term diffuse double layer describes the surface of the negatively charged particle and the dispersed layer of cations, the characteristics of this layer are that it is a thin layer of strongly water bonded and viscous, in addition the amount of cations is inversely proportional to the distance between the cations and the clay particle.
Sedimentary processes are those that produce, move, deposit and accumulate sediments and that intervene in the formation of sedimentary rocks. They are part of the sedimentary cycle and occur on the earth's surface or shallowly below the earth's surface.
Diagenesis are processes that alter a sediment when it is on or near the earth's surface. The alterations as a result of the movements of the Earth and the increase in pressure are metamorphic in nature; however, diagenetic changes gradually become metamorphic.
REFERENCES
- Barrios, Deeyvid Oscar Sáez. 2017. Origin and Formation of Soils. Soil Mineralogy. Panama, 2017.Clay Mineral Formation and Transformation in Rocks and Soils Eberl, DD 1984. Denver Colorado: Phil. Trans. R. Soc. Lond, 1984. 80225.Diagenesis in Clay Minerals - a Review. Keller, WD Missoury, ColumbiaSoga, Mitchell and. 2005. Soil Formation. John Wiley & Sons. 2005 Beatriz, Cabrera Rivera and Tamara. Geotechnical characteristics of the residual soils of the Cordillera de la Costa batholith. Undergraduate Thesis. 2007.Dictionary of Earth Sciences. Spain: Complutense, 2000. Torri, Silvana. slideshare.net. March 10, https://es.slideshare.net/Shvana/unidad-1a-45676959. Jorge, Nelly Lidia. slideplayer.es. 2016. http://slideplayer.es/slide/10258333/. Erosion, Transport and Sedimentation. María, Blog de. 2011 Hernández, Alberto.slideshare.net. July 24, 2010. https://es.slideshare.net/Alberkar/los-procesos-geolgic os-externa-y-el-reliieve-2008-9.
