Due to all these unique properties, clay minerals are gaining interest in different fields. Georgius Agricola — , the founder of geology, was seemingly the first who gave the definition of clay in It has been modified several times due to which the clay definition raises the questions related of constituents of clay and implicitly which was very important [ 1 ]. According to these societies, clay, a naturally occurring material, composed mainly of fine-grained minerals, become plastic in presence of water and become hard when dried or fired.
By this definition of clay, engineered clays and clay-like materials can be distinguished as clay fine grained minerals exhibiting plasticity in presence of water and become hard on drying and firing [ 2 , 3 ]. Clay is a soft, freely bound, fine grained natural rock or earthy material having diameter less than 0.
Based on the standard definition of mineral, clays are mainly inorganic materials except peat, muck, some soils, etc. During weathering, the content of feldspar is distorted by hydrolysis process results in formation of clay minerals such as kaolinites the primary minerals in kaolin clays and smectite the primary minerals in bentonite clays.
Clay can incorporate with one or more clay minerals even in presence of minute quantities of quartz SiO 2 , metal oxides Al 2 O 3 , MgO etc. The plasticity of clays are due to their particle size, geometry as well as content of water and become hard, stiff, coherent and non: plastic upon drying or firing.
Plasticity and hardness are greatly affected by the chemical composition of the material present in the clay. Clays can be molded in any form when they retain water. Clays are easily molded into a form that they retain when dry, and they become hard and lose their plasticity when subjected to heat. In all definition of clays, the particle size is a key parameter, no generally upper limit is accepted till now.
Although clays can be distinguished from other fine-grained soils on the basis of their size difference and mineralogy. The particle sizes of silts fine-grained soils that do not consist of clay minerals is larger than clays. Individual clay particles are always smaller than 0. The difference between silt and clay varies by discipline. Mostly, geologic clay deposits composed of phyllosilicate minerals having variable amounts of water present in the mineral structure.
The colloidal suspensions are formed when clays are immersed in water and flocculation occurs when they immersed in saline water.
Clays are divided into two classes: Residual clay: Residual clays are found in the place of origin and formed by surface weathering which give rise to clay in three ways:.
Solution of rocks, such as limestone, containing clayey impurities, which, being insoluble, are deposited as clay. Disintegration and solution of shale [ 8 ]. Transported clay, also known as sedimentary clay, removed from the place of origin by erosion and deposited in a new and possibly distant position. Clay minerals are the characteristics minerals on the earth found near planetary surface the surface where the outer crust of the object comes in contact with atmosphere environment with variable amount of ions like iron, magnesium, alkali metals, alkaline earth metals and other cations.
They are considered as important constituents of soil and form by diagenetic and hydrothermal alteration of rocks in presence of water [ 9 ]. They are commonly found in fine grained sedimentary rocks such as shale, mudstone and siltstone.
As water is essential for clay minerals formation, therefore, most of the clay minerals are known as hydrous alumino silicate or hydrous aluminum phyllosilicate. The formation of clay minerals is due to the chemical weathering of rock [ 9 , 10 ].
The chemical and structural composition of clay minerals is found to be similar to the primary minerals which originate from the crust of earth mainly from igneous or metamorphic rocks. Transformations may occur in ambient conditions. Although some of the most resistant primary minerals such as quartz, micas and feldspar may remain in soils whereas other less resistant primary minerals pyroxenes, amphiboles are susceptible to breakdown by weathering, thus forming secondary minerals.
The resultant secondary minerals are the formed due to either modification of the primary mineral structure incongruent reaction or neoformation through precipitation or recrystallization of dissolved constituents of primary minerals into a more stable structure congruent reaction.
These secondary minerals are most probably defined as phyllosilicates because, as the name suggest Greek: phyllon, leaf , they exhibit a platy or flaky structure with irregular edges; while one of their most important basic structural units is an extended SiO 4 tetrahedra sheet [ 11 ].
Clay minerals are found to be the most interesting class of minerals that have attracted substantial worldwide attention and investment in research and development. In , the nature of clay can be defined with advanced development in X-Ray diffraction technology used to investigate the molecular nature of clay particles.
Most of the chemical and physical properties of the soil including swelling - shrinking capacity, cation exchange capacity etc. Clay minerals are look like micas due to their chemical composition [ 12 ]. The properties that define the composition of clay minerals are derived from chemical compounds present in clay minerals, symmetrical arrangement of atoms and ions and the forces that bind them together. The clay minerals are mainly known as the complex silicates of various ions such as aluminum, magnesium and iron [ 13 ].
On the basis of the arrangement of these ions, basic crystalline units of the clay minerals are of two types: silicon — oxygen tetrahedron consists of silicon surrounding by four oxygen atoms and unite to form the silica sheet. Structure of tetrahedral and octahedral unit. The basic building block of tetrahedral sheet is a unit of Si atom surrounded by four oxygen atom known as silica tetrahedra. The tetrahedral sheet is formed by sharing of three oxygen of each tetrahedra with three nearest tetrahedra as shown in Figure 2.
These oxygen atoms are known as basal oxygen which connect pairs of all tetrahedra together more or less in one plane whereas the fourth oxygen atom remain free and form the bond with other polyhedral elements known as apical oxygen. Apical oxygens are all in a separate plane and provide a link between both tetrahedral and the octahedral sheet [ 15 ]. As only one apical O is present per tetrahedron therefore, each tetrahedron shares a corner with an octahedron in the octahedral sheet.
Arrangement of tetrahedral unit to form the tetrahedral sheet. Since, octahedral sheet are present in two forms: dioctahedral or trioctahedral sheet. When aluminum having three positive valences present in the octahedral sheet, only two-thirds of the sites are filled so that the charges will be balanced which results in formation of dioctahedral sheet. When magnesium having two positive charge valences is present, all three positions are filled to balance the charge which results in formation of trioctahedral sheet [ 15 ].
The octahedral sheet is formed by sharing of two oxygen of each octahedra when various octahedra linked together horizontally Figure 3 [ 16 , 17 ]. Arrangement of octahedral unit to form the octahedral sheet. The difference in the composition of clay minerals occurs very frequently when substitution of ions takes place within the mineral structure. This process is known as isomorphous substitution where one structural cation is replaced by another of similar size and this kind of replacement signifies the primary cause of both negative and positive charges in clay minerals.
The net charge of the clay mineral is determined by after balancing electron loss and gain within the structure. In most soils, the net negative charge exceed by a positive charge after substitution [ 18 ]. The aluminosilicate layers comprises of the basic structural units of phyllosilicates which is formed by the combination of tetrahedral and octahedral sheets bound by shared oxygen atoms.
Both the tetrahedral and octahedral sheets are the main components of phyllosilicates due to their leaf like or plate like structure, they are known as phyllosilicates which bound together by sharing of oxygen atoms into different layers. Based on number of tetrahedral and octahedral sheets and their arrangement, the phyllosilicates are divided into following categories including layer and chain silicates, sesquioxide and other inorganic minerals:.
Clay can be classified depending on the way that the tetrahedral and octahedral sheets are packed into layers. The major groups of clay minerals present in the soil environment include layer and chain silicates, sesquioxides, and other inorganic minerals as shown in Figure 4 [ 19 ].
Classification of clay minerals. A silicate comprising of planar octahedral layer bound to tetrahedral layer above and below with a distinctive repeating distance between t-o-t layers. These are the primary component of soils and are known as excellent trappers of water held between layers. Minerals within these groups are further categorized into dioctahedral and trioctahedral [ 11 ].
On the basis of number and arrangements of tetrahedral and octahedral sheets present in clay, the layer silicate are divided into three categories: type of clay mineral. Each individual layer is assembled from one tetrahedral SiO 4 and one octahedral sheet AlO 6. Kaolinite and Halloysite are examples under this category [ 20 ]. The rocks that are found to be rich in Kaolinite are identified as Kaolin or china clay [ 21 ].
The chemical weathering of aluminum silicate such as feldspar results in formation of a soft, usually white, earthy mineral dioctahedral phyllosilicate clay The dickite and nacrite are rare forms of kaolinite which are chemically similar to kaolinite but amorphous in nature.
Kaolinite is found to be electrostatically neutral having triclinic symmetry. The hydrogen bonding is found in between oxygen atoms and hydroxyl ions of the layers that are paired. Since, hydrogen bonding is weak, random movements between the layers are quite common results in lower crystallinity of kaolinite minerals than that of the triclinic kaolinite. The ideal structure of kaolinite has no charge.
Hence, the structure of Kaolinite is fixed due to the hydrogen bonding therefore; there is no expansion between the layers or have low shrink-swell capacity when clay is wetted. Due to the low surface area and little isomorphous substitution, Kaolinite has low capacity to adsorb the ions [ 15 ].
Dickite and nacrite are polytypic forms of kaolinite consisting of a double layer and have monoclinic symmetry. Dickite and nacrite differentiate themselves by different stacking sequences of the two silicate layers [ 23 ]. It is illustrated by its tubular form in contrast to the platy form of kaolinite particles. Dehydration occurs on mild heating of Halloysite and will irreversibly get transformed to kaolinite. The dehydrated form of Halloysite has basal spacing with thickness of a kaolinite layer approximately 7.
The difference of 2. Consequently, in hydrated form, the layers of halloysite are separated by monomolecular water layers that are lost during dehydration [ 23 ]. Serpentine: Serpentine is a group of hydrous magnesium-rich silicate minerals and a common rock-forming mineral having the composition Mg 3 Si 2 O 5 OH 4 [ 24 ].
Serpentine generally appears in three polymorphic forms: chrysotile, a fibrous type used as asbestos; antigorite, a variety exists in either corrugated plates or fibers; and lizardite, a very fine-grained, platy variety. Serpentine is usually grayish, white, or green due to iron replacing magnesium but may be yellow chrysotile or green-blue antigorite. It usually occurs along the crests and axes of great folds, such as island arcs or Alpine mountain chains. Normal occurrences are in altered peridotites, dunites, or pyroxenites; serpentinite is a rock consisting largely of serpentine.
Most of the layer silicate clays are commonly found in soils and based on the mica structure in which a single octahedral sheet sandwiched between two tetrahedral sheets and form an individual composite layer as shown in Figure 5. In dioctahedral and trioctahedral layer silicates, two and three octahedral sites are occupied respectively out of the three available sites in the half- unit cell single Si 4 O 10 [ 26 ].
Different types of clay minerals. These types of clay minerals consist of one octahedral layer sandwiched between two tetrahedral layers.
They are further characterized into two categories: Expanding clay minerals: Smectite group and Vermiculite. Expanding clay minerals: This group includes mainly smectite group of clay minerals and vermiculite clay mineral.
They are known for their interlayer expansion which happens during their swelling behavior when they are wet. Smectites are mainly based on either trioctahedral talc or dioctahedral Pyrophyllite structure and differ from these neutral structures due to the presence of isomorphous substitution in the octahedral or tetrahedral layer.
The Smectite group of clay minerals are further divided into Saponites trioctahedral and Montmorillonite dioctahedral. Another important member of the Smectite family is Bentonite. Bentonite clay is also known as sedimentary clay and has unique property of water retaining. The most prominent members of this group are Montmorillonite. Beidellite, nontronite, and saponite. The flake-like crystals of smectite e. Each layer is composed an octahedral sheet sandwiched between two tetrahedral silica sheets.
Slight attraction is found between oxygen atoms present in the bottom tetrahedral sheet of one unit and in the top tetrahedral sheet of another unit. This allows a variable space between layers, which is occupied by exchangeable cations and water.
Therefore, the exchangeable cations and water can easily enter the interlayer space resulting in the expansion of layers that may vary from 9. In Montmorillonite, magnesium ions are replaced aluminum ions in some sites of octahedral sheet and likewise, some silicon ions in the tetrahedral sheet may be replaced by aluminum ions.
This type of replacement is known as isomorphic substitution which give rise to a negative charge on the surface of clay minerals. Therefore, the layer charge density of these minerals is found to be in between 0. The general structural formula of smectite group of clay minerals is Na, Ca 0. The structure, chemical composition, exchangeable ions are responsible for their several unique properties such as high cation exchange capacity, high surface area and high adsorption capacity.
The quantity of cations required to balance the charge deficiency induced by these substitutions is referred to as the cation exchange capacity CEC. The CEC for Montmorillonite ranges from 80 to milliequivalent per grams. Montmorillonite clays have very poor thermal stability. These minerals show some prominent characteristics like high cation exchange capacity, swelling and shrinkage capacity.
When smectite dominated soils e. Chemical composition of the unit cell has been represented as [ Si 8. It is a versatile mineral due to its platelet structure. The platelet consisting of a tetrahedral silicon oxide layer in which some silicon replaced by trivalent cations sandwiched between two octahedral aluminum oxide layers in which aluminum replaced by divalent cations.
Definition: Bentonite is defined as a naturally occurring material that is composed predominantly of the clay mineral smectite. Most bentonites are formed by the alteration of volcanic ash in marine environments and occur as layers sandwiched between other types of rocks. The smectite in most bentonites is the mineral montmorillonite, which is a dioctahedral smectite but occasionally other types of smectite may be present.
It is the presence of smectite which imparts the desirable properties to bentonites, although associated factors such as the nature of the exchangeable cations in the interlayer also affect properties. The image on this page shows a geosynthetic liner with bentonite granules as fill. Clays and Minerals.
If the glaze is to be used as a base for colored glazes the addition of 5 percent of an opacifier such as zirconium silicate will produce a warm white suitable for this purpose. A raw lead glaze that has been used very successfully on a number of types of body within the temperature range of cone 07 to cone 04 is given below. It is probable that the glaze could be used over a much longer range. A high-temperature glaze that has produced excellent results on a siliceous body is given below.
This glaze was used at cone 7 and cone 9, but should be usable from cone 6 to Colored glazes can be made by adding the correct oxides or stains. Volcanic ash glazes are used in at least three potteries in the State and by a number of schools. The chief advantage in the use of volcanic ash is the low cost, although there are the added advantages of an unusually long firing range and the fact that the colors in volcanic ash glazes are somewhat softer than those obtained with the conventional materials.
Kansas potteries also find that advertising the use of volcanic ash glazes attracts customers. The substitution of volcanic ash in ceramic glazes for equivalent amounts of other materials produces very little difference in the final glaze, although the firing temperature may be slightly lower due to the surprisingly low fusion temperature of the ash.
In ceramic bodies, however, the results are not so predictable. Generally the results are more beneficial than would be expected. A number of test bodies with different types of clays and shale and with varying amounts of volcanic ash indicate that from 7 to 15 percent volcanic ash additions to a shale or red-firing clay body lowers the vitrification temperature, increasing the firing range for a matured body, and producing a greater rigidity in the ware at the maximum temperature.
These qualities produced by the volcanic ash additions permit economy in use of fuel, and reduce losses in the kiln due to the less critical temperature range requirements and the ability of the ware to stand up under its own weight at the maximum temperatures attained in the kiln. Not all clays and shales react with equally favorable results.
Some materials are benefited only in that the firing temperature is reduced. The benefits of volcanic ash additions to sewer pipe bodies have received considerable attention. A group of clay plant operators sponsored a project at the Engineering Experiment Station at Ohio State University to test the value of additions of volcanic ash to sewer pipe bodies.
Everhart, research professor in charge of this project, reported to us that definite benefits were obtained by the use of volcanic ash. In a letter accompanying the report Everhart summarizes the effects of volcanic ash as follows: "It seems to have a somewhat stabilizing influence on the mix to which we added it, and might be of considerable value for use in local clay and shale mixes having a short firing range.
We attribute this influence to the fact that it forms a very viscous glass which remains so over a long range of temperatures. Pence personal communication of the University of Texas reports that very beneficial results are realized from the use of volcanic ash in a sewer pipe body in a Texas plant.
Somewhat similar results are obtained with additions of volcanic ash to pottery or whiteware bodies, although in this case the fired color of the body is darkened slightly by the iron content of the ash. The use of volcanic ash in amounts ranging from 10 to 25 percent lowers the firing temperature required, or to look at the matter from another angle, it makes it possible for the art potter whose maximum temperature is limited to produce hard-fired ware that does not leak or craze.
In general the casting properties of pottery bodies are improved with the addition of volcanic ash. This is due largely to the size and shape of the particles. At least one pottery in Kansas is using volcanic ash with Kansas clay in the casting body and produces a vitrified ware at cone 4. Volcanic ash performs the same function in glass and in vitreous enamels as it does in ceramic glazes.
Due to the iron oxide of about 1. Volcanic ash has been seriously considered as an ingredient in fiber glass batches and in foam glass where the slight darkening of color is of minor importance.
If used in the production of fiber glass the problem of preventing the disintegration of the platinum dies by the iron present in the ash would have to be solved. Laboratory trials with volcanic ash as an ingredient in vitreous enamel were made by one of the major manufacturers of sanitary ware.
The laboratory reported that the cream-colored and ivory-colored enamels produced with additions of volcanic ash were slightly superior to those produced with feldspars, but that due to the distance the ash would have to be shipped to their plants no saving in cost would be realized.
The Oklahoma Geological Survey has investigated the possibility of producing cellular products similar to Foamglas and an extremely lightweight aggregate consisting of bloated individual particles of volcanic ash Burwell, The cellular product was produced by heating volcanic ash to a high temperature in refractory molds.
The resulting product, which was named "pumicell" by the Oklahoma Survey, is a glass containing small disconnected cells of air. It has high insulating value, and can be sawed or nailed. The bulk density of the product ranges from 45 to 90 pounds per cubic foot as compared to a true specific gravity of 2. The volume of closed cells in the product was as much as Experimental bloating of Kansas volcanic ash in the laboratory of the State Geological Survey of Kansas indicates that the Kansas ash has the same bloating characteristics as the Oklahoma material.
The lightweight aggregate produced in the laboratory of the Oklahoma Geological Survey is similar to expanded perlite, although the method used to "pop" the volcanic ash was not the same as that used to expand perlite. The volcanic ash was expanded by introducing a stream of volcanic ash into the air intake of an inspirator-type gas burner. The product consists of glassy beads containing one or more bubbles.
The bulk specific gravity of the "popped" volcanic ash ranges from 0. Products made from this material insulate against the transmission of heat, sound, and electricity. It can be used in acoustical and insulating plasters, wall board, lightweight blocks, and slabs. The State Geological Survey of Kansas has been able to produce a similar expanded or "popped" product from Kansas volcanic ash of Pleistocene age.
Attempts to produce a similar product from Pliocene ash were not successful. Additional testing is planned, and the results will be published in a Survey bulletin in An expanded volcanic ash product similar to perlite is being produced at Hutchinson, Kansas, under the trade name Mira-Colite. The method used for production of this material is not known in detail.
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