22.09.2019
Clays and clay minerals. Basic properties of clay minerals
Currently, there is no generally accepted classification of clay minerals. Individual researchers approach their classification from different positions and attach different significance to certain structural features of minerals. Therefore, it is most convenient to consider, as is done in many manuals, the structure of the most common clay minerals and their main varieties.
Based on the nature of the connection and alternation of hetrahedral and octahedral networks in the structure of clay minerals, they can be divided into the following main groups, represented in nature by the most common types of clay minerals;
- kaolinite group,
- group of smectites (montmorillonites),
- illite group (hydromica),
- a group of chlorites.
The minerals of the latter group are not clayey, but they are present in clayey rocks and have much in common with clay minerals in structure.
Kaolinite group. The structure of kaolinite is an endless alternation of packets, reminiscent of the pages of a thick book, each of which consists of two layers; tetrahedral and octahedral. The layers are connected into packets due to common oxygen cations that simultaneously belong to the tetrahedron and octahedron of the corresponding layers (Fig. 10.3). The centers of two out of every three octahedra are occupied by Al3+ cations. Thus, the octahedral network of kaolinite is dioctahedral. There are no ionic bonds between neighboring packets in the kaolinite structure and they are held in a single, infinitely alternating layered crystal structure by hydrogen bonds acting between the groups (OH) of the free surface of the octahedral networks and the adjacent oxygen atoms of the free surface of the tetrahedral networks of the neighboring packet. The structural formula of kaolinite is Al4Si4O10(OH)8. This corresponds to the following oxide ratio; SiO2 - 46.56%; Al2O3 - 39.50 and H2O - 13.94%. Chemical analyzes of kaolinites show that isomorphic substitutions in their structure are extremely insignificant. The distance between the corresponding surfaces of the tetrahedral or octahedral networks of two adjacent packets, i.e., the interplanar distance, for kaolinite is 7.1-7.2 A.
In table Figure 10.1 shows the characteristic interplanar distances and intensities of X-ray reflections of kaolinite.
In cases where kaolinite is present in samples in the form of a mixture with chlorite, the interplanar distance of which is d001 = 14.3 A, it may not be noticeable, since for chlorite d002 = 7.15 A, i.e., almost equal to d001 of kaolinite. Therefore, in the presence of chlorite, in addition to the natural sample, a diffraction pattern of the sample treated with warm 10% hydrochloric acid. When treated with acid, chlorites dissolve, but kaolinite remains unchanged and can be identified by characteristic reflections. In table Table 10.2 shows the effect of various sample treatments on clay minerals, which make it possible to determine clay minerals in mixtures.
A detailed study of the nature of the unit cell of kaolinite showed that it belongs to the triclinic system.
Kaolinite gives a very characteristic thermogram during thermographic analysis. The differential heating curve shows a clear endothermic reaction corresponding to the loss of hydroxyl water, starting after 400°C and reaching a maximum at 600°C (Fig. 10.4), as well as an exothermic reaction, apparently associated with the formation of crystalline alumina (Al2O3) , the maximum of which occurs at 950°C.
Examination of kaolinite particles in transmission and scanning electron microscopes shows that kaolinite is usually represented by more or less well-formed hexagonal (pseudo-hexagonal) lamellar crystals, often with predominant elongation in one direction (see Fig. 10.5).
Polymorphic modifications of kaolinite are dickite and nacrite, which have the same composition as kaolinite - Al4Si4O10(OH)8. According to J. Gruner, dickite is a monoclinic mineral. Nakrit, according to S. Hendricks, can be classified as a rhombic system.
The formation of dickite is characteristic of cements of clastic rocks at the stage of late catagenesis-metagenesis. It can occur together with kaolinite in clayey rocks and, having, like kaolinite, a lamellar pseudohexagonal habit (electron microscopy), the shape of the particles is practically indistinguishable from kaolinite. However, according to the results of X-ray phase (Table 10.3) and thermographic (see Fig. 10.4) analyses, dickite is diagnosed quite confidently.
Nakrite is a rare mineral. It is present in rocks. exposed to low-temperature hydrothermal solutions.
Close in structure to kaolinite is halloysite, the formula of which Al4Si4O10*(OH)8*4H2O indicates the presence of interpacket water in the mineral. Halloysite has a characteristic thermogram (see Fig. 10.4), which clearly shows an endothermic reaction in the range of 60-100°C, indicating the loss of interpacket water. The presence of water molecules in the interpacket voids leads to an increase in the interplanar distance of halloysite to 10-10.1 A (see Table 10.3). Unlike kaolinite and dickite, halloysite particles have an elongated, tubular shape(see Fig. 10.5). In clayey rocks, halloysite can occur together with kaolinite and montmorillonite, and in weathering crusts it can form independent accumulations.
Together with kaolinite and halloysite, allophane can be found - an X-ray amorphous clay mineral of colloidal nature, which is an amorphous colloidal mixture or a solid solution of free alumina and silica, formed during their joint coagulation. The chemical formula of allophan is mAl20*nSiO2*pH2O. The mineral was found in weathering crusts, coal strata, bauxites, brown iron ores and other rocks.
Group of smectites (montmorillonite). To designate minerals that have a similar structure and form one structural group, a typical representative of which is montmorillonite, the term “smectites” is often used. Along with this, the terms “montmorillonite minerals” or “montmorillonites” can be found as a group name in the geological literature.
The structure of smectite (montmorillonite) can be represented as an endless alternation of flat packets, each of which has a three-layer structure: in the middle there is an octahedral aluminum-oxygen-hydroxyl layer, at the top and bottom there is one tetrahedral silicon-oxygen layer (see Fig. 10.3). The tetrahedral networks are rotated so that the vertices of the tetrahedrons are directed inward towards the octahedral layer. At the vertices of octahedra, common with tetrahedra, oxygen atoms are located instead of hydroxyl groups (OH). The structure is dioctahedral. Due to the fact that the surfaces of three-layer packets are formed by the neutral bases of tetrahedra, the connection between the packets is very weak; they are held in the three-dimensional crystal structure only by van der Waals forces. Therefore, water molecules are located in the interpacket space, causing expansion of the crystal lattice in the direction of the c axis, i.e. leading to an increase in the interplanar distance, which for smectites (minerals of the montmorillonite group) is a variable value, depending on the degree of saturation of the interpacket space with water molecules, some organic compounds or cations.
The theoretical structural formula of idealized smectite (without taking into account isomorphic substitutions) is quite simple - Al2Si4O10(OH)2*nH2O. The formulas of real smectites always differ from this idealized formula, since in tetrahedral networks part of Si4+ (up to 15%) is replaced by Al3+, less often by Fe3+; and in the octahedral network, part of the Al3+ (and sometimes all of the Al3+) is replaced by Mg2+ or Fe3+. When octahedral aluminum is completely replaced by Mg2+, the mineral acquires the trioctahedral structure of the octahedral layer. With isomorphic substitutions, an excess negative charge of the packets arises, which is usually compensated by Na+ and Ca2+ cations, sometimes partially by K+ or Mg2+, which, together with water molecules, fill the interpacket space of the crystal lattice.
The widespread development of processes of isomorphic substitution of Al in octahedra and Si in tetrahedra determines the formation large quantity varieties of clay minerals belonging to the smectite group.
In table Figure 10.4 shows the composition of the main minerals from the smectite group.
In addition to those listed in the table, there are many other minerals classified as smectites, including relatively rare ones: volkonskoite (chromium smectite), soconite (zinc smectite), etc.
Between such minerals as montmorillonite and beidellite, montmorillonite and nontronite, beidellite and nontronite, etc., there may be isomorphic series of minerals of variable composition, a generally accepted classification and nomenclature of which has not yet been developed.
The most common mineral in the smectite group in nature is montmorillonite, after which the entire group is often called. Depending on the cations and the number of water molecules filling the interpacket spaces, the structure of montmorillonite is characterized by different interplanar distances. Thus, the structure of montmorillonite with Na+ cations and one molecular layer of water has an interplanar distance of approximately 12.5 A. Montmorillonite with Ca2+ cations usually contains two molecular layers and has an interplanar distance of 15.5 A (Table 10.5).
The presence of montmorillonite with an interplanar distance 001 = 14.0-14.5 A is often noted in samples. To determine montmorillonite, according to X-ray phase analysis, important role plays the ability of the lattice of this mineral to expand along the c axis, i.e. the ability to increase the interplanar distance when the interpacket spaces are saturated with molecules of organic compounds such as ethylene glycol and glycerin. Regardless of the initial interplanar spacing of natural montmorillonite, after its saturation with ethylene glycol, the interplanar spacing increases to 17.0A. If the sample is saturated with glycerol, it increases to 17.7-17.8 A (Table 1.0.6). Calcination of montmorillonite samples for two hours at a temperature of 600°C leads to a decrease in the interplanar distance to 9.5-10.0 A, which also helps to identify the mineral (see Table 10.2).
When comparing diffraction patterns of natural samples and samples saturated with ethylene glycol or glycerol, the presence of montmorillonite is easily established by increasing the interplanar distance even in mixtures with other clay minerals. For more accurate diagnosis of varieties of smectite minerals, chemical analysis data is used, from which structural formulas minerals.
The results of their thermographic analysis provide significant assistance in identifying smectite minerals. The thermograms of all smectites clearly show an endothermic reaction with a maximum between 150° and 200°C, associated with the loss of interpacket water from the mineral lattice. The nature of thermograms of individual minerals of the smectite group is shown in Fig. 10.4.
Electron microscopic examination of montmorillonite shows that its particles do not have crystallographic outlines and are chaotic, vague masses with blurry, indistinct edges (see Fig. 10.5), apparently formed by aggregates of superimposed tiny scaly particles with a thickness of approaching the thickness of an elementary packet.
Close in structure to smectites are vermiculites, often identified as an independent group of minerals. The structure of vermiculites is three-layer, consisting of two external tetrahedral networks and an internal octahedral network (for the structure of montmorillonite, see Fig. 10.3). In the interpacket space, Mg, Ca and some others, as well as water molecules, are present as exchange cations. General formula of vermiculites
where x = 0.5/0.7 to 1.0.
In clay rocks, finely dispersed vermiculites are often present as an admixture to other clay minerals or form mixed-layer formations such as montmorillonite - vermiculite, chlorite - vermiculite, etc. The interplanar distance d001 of vermiculites is 28-29 A. The diffraction patterns usually clearly show reflection 002, equal to 14. 0-14.5A, due to which vermiculite minerals are determined in the presence of montmorillonites or chlorites. Vermiculites differ from montmorillonites by the absence of an increase in the interplanar distance when treated with glycerin after preliminary saturation of the mineral with magnesium cations; and from chlorites - by decreasing d001 to 9.4-10.0A after calcination at 600°C (see Table 10.2).
Thus, vermiculites of clay rocks have the structure of illites and smectites, and the connections between the packets in vermiculites are weaker than in minerals of the illite group (hydromica), but stronger than in minerals of the smectite group (montmorillonite).
Illite group (hydromica). The term “illite” was proposed by American researchers R. Grim, R. Bray and W. Bradley (1937) to designate various mica-like clay minerals. Currently, in this understanding, it is widely used in foreign geological literature. In Russia, the term “hydromica” is more often used to designate mica-like clay minerals. In this case, illite is understood as a finely dispersed clay mineral, which is a hydrated analogue of muscovite.
The structure of illites is similar to the structure of smectites (cf. Fig. 10.6 and 10.3). It is formed by alternating three-layer packets, each of which consists of two tetrahedral silicon-oxygen networks, with the vertices of the tetrahedrons turned towards each other and an octahedral aluminum-oxygen-hydroxyl layer enclosed between them. The idealized formula of illite, which actually coincides with the formula of muscovite, KAl2(AlSi3)O10(OH2), shows that as a result of the isomorphic substitution of part of Si4+ in silicon-oxygen tetrahedra with Al3+, an excess negative charge arises, which is compensated by K+ cations. The latter are located in the interpacket spaces in hexagonal " depressions" existing on the surface, formed by grounds tetrahedrons, and rigidly bind adjacent packets, preventing the expansion of the lattice along the c axis. The interplanar distance characteristic of illites is 10 A. It does not change either when the mineral is saturated with ethylene glycol or glycerol, or after it is calcined at a temperature of 600 ° C (see Table 10.2).
Mica-like dioctahedral clay minerals (illites) differ from muscovite in a lower degree of substitution of Si4+ for Al3+ and, accordingly, in a lower content of potassium, which compensates for the excess negative charge of the packets. Thus, in muscovite the theoretical K2O content is 11.8%, while in illites it in most cases ranges from 3-4 to 8%. In illites, isomorphic substitutions of aluminum in octahedra with Fe3+, Mg2+, Fe2+, etc. are quite widely developed. The general formula of minerals of the illite group can be presented in the form
where x = 0.5/0.75.
In the interpacket complex, along with the significantly predominant k, there are water molecules and sometimes a certain amount of Na, Ca, and Mg cations is noted. As the degree of substitution of Al3+ in octahedra with Fe3+, Fe2+ and Mg2+ increases, a clay mineral known as glauconite appears. According to S. Hendricks and K. Ross, the average composition of dioctahedral glauconite without taking into account interpacket water is expressed by the formula
Mica-like clay minerals - illites - are the main components of the vast majority of clay rocks. The overwhelming mass of clayey rocks consists of minerals of the illite group and mixed-layer formations, in the composition of which illites play a significant role. It has been established that clayey rocks contain three polytypic varieties of illite minerals, differing from each other in the nature of the overlay of layers that form their crystal lattice;
- polytype 1M - illites with an interplanar distance of 10A, possessing a monoclinic crystal lattice, giving clear sharp symmetrical peaks in diffraction patterns. This also includes 10-angstrom illites with a disordered lattice, i.e., poorly crystallized (subtype 1Md). In their diffraction patterns, they are characterized by low diffuse reflections, “spreading out” towards large angles of 20;
- polytype 2M1 (M1 means one of two theoretically possible varieties) - illites of the mo1ucline system, the unit cell of which covers two packets with an interplanar distance d001 = 20A;
- polytype 3T - illites of trigonal system with a unit cell including three packets with an interplanar distance d001 = 30A. The 3T polytype is much less common than 1M, (1Md) and 2M1.
It is not always possible to distinguish between different types of illustrators based on X-ray phase analysis of finely dispersed fractions. The fact is that pure, monomineral accumulations of illite minerals are very rare. In most clayey rocks, illites are present in a mixture with other clay minerals, chlorites, and in the form of mixed-layer formations.
G.V. Karpova provides data from separate X-ray analysis of illites of the 1M (1Md) and 2M1 polytypes (Table 10.7).
The thermograms of illite (see Fig. 10.4) in the temperature range 100-200°C show an endothermic reaction associated with the loss of interpacket water. The second endothermic reaction, corresponding to the loss of hydroxyl water by the mineral, begins around 450-500 °C and has a maximum between 550-650 °C. The intensity and temperature range of this reaction varies among different illites. The third endothermic reaction, apparently associated with the destruction of the illite structure, occurs between 850° and 950°C. Finally, around 1000°C, a weak exothermic reaction of the formation of alumina and spinel is observed.
Studying the shape of illite particles using an electron microscope shows that clay rocks contain two types of illite particles:
- subisometric lamellar particles belonging to the 2M1 and 1M polytypes, according to a number of researchers, entering the sediment due to the erosion of older sedimentary and metamorphic rocks;
- elongated lamellar, “split-like” particles (Fig. 10.5) of the 1M (1Md) polytype, having an authigenic origin.
Chlorite group. Minerals of the chlorite group have a four-layer structure (Fig. 10.6), and the elementary package consists of two parts: a three-layer part, similar to illite packages, and another layer of magnesium-hydroxyl octahedra (brucite layer). The interplanar distance of finely dispersed chlorites of clayey rocks is 14.0-14.3. The composition of chlorites is significantly different due to the widespread phenomenon of isomorphic substitutions within tetrahedral and octahedral networks. The general formula of chlorites is
In clayey rocks, finely dispersed chlorites are always present in a mixture with clay minerals or in the form of mixed-layer formations such as chlorite-montmorillonite, illite-chlorite, etc. The presence of chlorites in clay fractions is detected by characteristic X-ray reflections, the main of which are reflections from the basal plane 001, especially reflections from plane 001 = 14.0-14.3 A (Table 10.8).
In cases where the rock contains a mixture of clay minerals and chlorites, the latter are difficult to distinguish from montmorillonites having doo1 = 14.0-14.5 A or even kaolinites (d001 = 7.15 A), if the reflection of chlorite 14.3 A is unclear . To control, the samples are treated with warm hydrochloric acid HCl, in which the chlorites are dissolved and their reflections on the diffraction patterns disappear accordingly, as well as the samples are saturated with glycerol, after which, if montmorillonites are present in the samples, reflections 001 = 17.8 A appear (see Table 10.2).
A group of mixed-layer formations. As studies of various clay rocks have shown, clay minerals are widespread in them, the crystal lattice of which is an alternation of packets of illite, montmorillonite and vermiculite structures with each other or with packets of chlorite structure. Such clay minerals are called mixed-layer minerals. They usually alternate between two types of packages; illite-montmorillonite, illite-chlorite, chlorite-vermiculite, etc. Mixed-layer minerals with alternating two-layer packets have not yet been reliably established.
There are two main types of mixed-layer formations.
Ordered formations. Packets of different compositions alternate regularly in them: ABABAB or ABBABBABBb, etc. Ordered mixed-layer formations are minerals of a certain composition. Their interplanar distance is equal to the sum of the interplanar distances of alternating packets. The diffraction patterns show a series of corresponding basal reflections 001, 002, 003, etc. Some mixed-layer minerals received special names. For example, corrensite is a natural alternation of chlorite and montmorillonite packets, bravaisite is illite and montmorillonite, and rectorite is vermiculite and pyrophyllite.
Disordered formations. Packets of different types alternate randomly, irregularly: ABAAAAABABBB, etc., which greatly complicates the study of the details of the structure of such minerals. Decoding diffraction patterns obtained from disordered mixed-layer structures is often very difficult. difficult task. Disordered mixed-layer formations, especially of the illite-montmorillonite type, are extremely widespread in sections of clayey strata.
In Fig. Figure 10.7 shows a diagram proposed by J. Luca, T. Kamets and J. Millot, showing the interplanar distance of the main clay minerals, mixed-layer formations and changes in these interplanar distances after various processing of the samples.
39. Clay minerals (general properties). What explains the moisture holding capacity of clays? Their sorption properties.
Clay minerals. Clay minerals are widespread in sedimentary rocks. They constitute a large and complex group of layered and layered-ribbon silicates and aluminosilicates. Their structure is layered or layered-ribbon. Separate layers are formed by interconnected tetrahedrons and octahedra. Oxygen ions are located at the vertices of the tetrahedrons, and silicon ions (sometimes aluminum in quadruple coordination) are located in the center. Oxygen and hydroxyl ions are located at the vertices of the octahedra, in the center -
aluminum, iron, magnesium (six-six coordination). Octahedral layers can be completely populated (trioctahedral) and partially populated - two out of every three are populated (dioctahedral). These layers form two-layer (one layer of tetrahedra and one layer of octahedra) and three-layer (two layers of tetrahedra with a layer of octahedra sandwiched between them) packages. The connection between the layers is carried out through oxygen and hydroxyl, which are the common vertices of tetrahedrons and octahedra. The spatial lattice of kaolinite is a set of two-layer packets with a thickness (interplanar distance) of 0.71-0.72 nm. Basal reflections 001 first order 0.71 -0.72, second - 0.355-0.360, fourth - 0.1775-0.1800 nm.
For hydromica, the lattice consists of a set of three-layer bags with a thickness of 1.0- 1,02 nm. Basal reflections OO1 first order 1.00-1.02, second - 0.50-0.51, fourth - 0.250-0.255 nm.
The spatial lattice of montmorillonite is formed by three-layer packets, between which are layers of water and exchangeable cations. The content of the latter can vary greatly, therefore the interplanar distance of montmorillonite varies widely - from 0.96-1.001 nm in the absence of water and exchangeable cations to 1.7-1.8 nm or more with a high content of water and exchangeable cations (average the value at normal humidity is approximately 1.40-1.50 nm).
Along with ordinary clay minerals, there are more complex formations - mixed-layer intergrowths of minerals. The spatial lattice of such intergrowths consists of packets belonging to various minerals: montmorillonite and chlorite (U = 2.80 nm), hydromica and kaolinite (U = 1.70 nm), montmorillonite and kaolinite (c1= 2.10-2.30 nm), etc. These mineral formations are peculiar “hybrids” and are considered by a number of scientists as epitaxial accretion. In studying them especially great importance has x-ray analysis - the only method that allows you to identify these intergrowths.
By origin, clay minerals can be both authigenic and allotigenic formations. Due to their high degree of dispersity, their diagnosis is difficult using conventional methods of crystal-optical and chemical analysis. The study of clay minerals during mass petrograph work should be comprehensive using optical, chromatic and droplet analyses. In parallel, some of the samples should be studied by precise methods: x-ray, thermal and electron microscopy. A summary of the optical and some other properties of clay minerals is given in Table. 72-74.
The common features of all clay minerals are: 1) the small size of their crystals; 2) chemical composition (AI2O3, SiO2, H2O, sometimes K, and AI and Si in some minerals are replaced by other elements, especially Mg, Fe); 3) lamellar or scaly shape due to the structure of the lattice, and 4) some optical properties - low refractive indices, mostly slightly higher, rarely slightly lower, than those of Canada balsam; crystalline ones have a monoclinic system.
Hardness (2.5) and sp. weight (2.40-2.59) are determined precisely only for kaolinite. The color of kaolinite and halloysite is white (colorless); other minerals of this group sometimes have a yellowish, reddish, bluish or greenish color.
PROPERTIES OF CLAY ROCKS
Knowing the factors that determine the properties of clayey rocks and methods for assessing mineral composition and microstructure, we will try to explain the nature of some important and very specific properties of clays that are of great importance in people's lives.
Swellability
Swelling is the ability of clay rocks to increase in volume during interaction with water or aqueous solutions. The swelling process is accompanied by an increase in humidity, rock volume and the appearance of swelling pressure.
The swelling of clay rocks is an important property that must be taken into account when carrying out construction work and operating engineering structures. Underestimating the swelling ability of clays can lead to serious consequences and accidents. Explaining the nature of clay swelling, it should be noted that this process takes place in two stages: the first stage is adsorption or intracrystalline swelling, the second is macroscopic or “osmotic” swelling. At the first stage, clay rock absorbs moisture due to the adsorption of water molecules by the surface of clay particles and the interlayer spaces of the crystal lattice of clay minerals. This stage has virtually no effect on the change in rock volume. In the second stage of swelling, moisture absorption is carried out using osmotic pressure. It occurs near the surface of clay particles due to the excessive concentration of numerous exchangeable cations dissociated (removed) from the surface of clay particles into the solution. The main increase in the volume of the swelling clay occurs precisely at this macroscopic stage.
The magnitude and nature of swelling of clayey rocks are determined by many factors, the main of which are mineral composition, dispersion and structure. Clay rocks that contain clay minerals with a mobile crystal structure (for example, montmorillonite) have the greatest swelling; minerals with a more rigid crystal structure (kaolinite) have the least swelling. The swelling of clays is also strongly influenced by their structure, and the nature of the structural bonds is of decisive importance.
Clay rocks with a predominant orientation of structural elements are characterized by pronounced swelling anisotropy. The greatest swelling is observed in the direction perpendicular to the orientation of the particles. During the swelling process, a significant restructuring of the initial microstructure of the clay rock occurs.
It is particularly difficult to consider the strength properties of clayey rocks due to their specific behavior when interacting with water. The loss of strength when clays are moistened, when they turn from dense and high-strength rocks into plastic or fluid bodies, is well known.
a group of aqueous silicates that make up the bulk of clays and determine their physicochemical, mechanical and other properties. Gems are a product of weathering mainly of aluminosilicates and silicates of igneous and metamorphic rocks on the surface. During the weathering process, minerals undergo stage-by-stage transformations in their structure and chemical composition depending on changes in the physicochemical conditions of the weathering and sedimentation environment. The particle sizes of hydrocarbons in clays for the most part do not exceed 0.01 mm. According to the crystal structure, hydrocarbons are classified as layered or pseudolayered silicates. In the crystal lattices of typical hydrocarbons, networks of silicon-oxygen tetrahedra (silicon ions in quadruple coordination) alternate with networks of hydroxyl octahedra, in the center of which there is an atom of aluminum, iron, or magnesium; divalent magnesium fills all octahedra (trioctahedral silicates), and trivalent aluminum only two out of three (dioctahedral silicates).
G. stones with a two-story structure are formed by tetrahedral and octahedral networks - the Kaolinite group, for example, kaolinite, dickite, nacrite, halloysite; Hydromicas with a three-story structure consist of two outer tetrahedral and middle octahedral networks - a group of hydromicas (See Hydromicas), for example hydromuscovite and glauconite (a potassium atom is located in the interlayer spaces); Montmorillonite group, for example Al-montmorillonite and Fe-montmorillonite (nontronite) (water and exchange cations in the interlayer spaces); group of chlorites (See Chlorites) - the structure alternates three-story layers and interlayer spaces (octahedral networks). G. m. of a more complex structure are also known.
Crystal chemical differences in the structure of gemstones correspond to certain differences in their chemical composition. Because of this, the properties of hydrocarbons differ sharply. For example, montmorillonite minerals have a very high exchange capacity and adsorption properties, while these properties are weakly expressed in kaolinite minerals. G. m., belonging to the group of hydromicas, sharply increase in volume when heated. To diagnose G. m., infrared spectroscopy, chemical x-ray, electron diffraction, electron microscopic, and thermal methods are used.
Lit.: Ginzburg I.I., Rukavishnikova I.A., Minerals of the ancient weathering crust of the Urals, M., 1951; X-ray methods of studying and structure of clay minerals, trans. from English, M., 1965.
V. P. Petrov.
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Great Soviet Encyclopedia
"Clay minerals" in books
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From the book Relief press in 3 months author Tolkachev Alexey IvanovichMinerals After water, the most important substances for cell life are minerals. The minerals that you should pay attention to are potassium, sodium, magnesium and calcium, because these are the ones that humans need in large quantities. In the life of the cell, as well as for its
Clay minerals plugging the pores, mainly illite fibers (Fig. 3-14c), are bound throughout the pore space. This type is the main reason for the reduction in permeability, since plugging is most easily achieved in the ducts, and it also reduces the pore size. The effect on porosity is less because microporosity is maintained between very fine fibers.[...]
Clay minerals in shelf sediments are primarily clastic in origin, and their distribution partly reflects differences in source. The montmorillonite-rich sediment in the north comes from lime-rich soils, while the kaolinite-illite-montmorillonite clays of the south reflect their origin in more alkaline soils. The distribution of clays along the shelf is also different, influenced by the fact that montmorillonite is deposited predominantly in deeper, offshore waters. Illite and kaolinite are concentrated closer to the shore, the same ratios are usually observed in ancient sections.[...]
Clay layered minerals can also reversibly absorb and release oxyhydryl groups. In addition, due to the special location of these groups on the surface of clay particles, they have specific mobility. These properties distinguish the OH„-groups of clay minerals from adsorbed water and made it possible to distinguish them into an independent group - “interlayer water”.[...]
Clay minerals of the hydromica and montmorillonite group have an important ability to accumulate chemical elements necessary for the development of herbaceous plants. Therefore, in the conditions of northern forests, rocks rich in these minerals are more favorable for the formation of sod-podzolic soils than rocks devoid of supergene silicates, on which podzolic soils are formed. Overfilling the soil-forming rock with detrital quartz creates conditions for a deficiency of nutrients for plants. This is also true for rare and dispersed chemical elements. Suffice it to recall the phenomenon of a lack of copper and some other trace elements in leached soils formed on fluvio-glacial and ancient alluvial sand deposits.[...]
Clay minerals are capable of sorbing non-ionic water-soluble substances contained in wastewater, such as polymers such as polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP). These substances are widely used in various industries (in particular, textile, etc.). The molecules of these polymeric substances are practically non-biodegradable. Smectites, including montmorillonite, illites and other clay minerals, are capable of actively sorbing PVA and PVP of various molecular weights from aqueous solutions (Fig. 2.3.5).[...]
Clay minerals actively absorb pesticides and other low molecular weight organic pollutants. The mechanism of sorption and its intensity depend on the chemical structure of molecules and aqueous molecular complexes of pesticides, in particular the presence of ionic and nonionic groups. Ionogenic (cationic) pesticides and other low molecular weight organic pollutants are most actively sorbed. However, there is evidence that montmorillonite is capable of sorbing nonionic pesticides through an ion exchange mechanism. The amount of sorption of pesticides by clay minerals is greatly influenced by the pH of the pore solution (Fig. 2.3.8).[...]
The clay minerals covering the pores (essentially illite, chlorite, and montmorillonite) form a thin layer of flakes on the pore walls, parallel or perpendicular to the pore wall (Fig. 3-14b), but the growth does not extend far into the pore space. Significant microporosity may be present between the scales, although the pore diameter is less than 1 cm. This type of authigenic clay mineral significantly reduces permeability and also affects many electrical properties of the rock, since it can greatly increase the surface area. [...]
Clay minerals are secondary aluminosilicates with the general chemical formula “SiO2Al2O3-tH20 and a characteristic molar ratio SiO2:Al2O3, varying from 2 to 5. [...]
The reserves of clay minerals in the USSR are practically inexhaustible. In particular, according to M. S. Merabishvili and G. A. Machabeli, about 400 deposits and occurrences of bentonite clays are already known on the territory of the Soviet Union. If we take into account the low cost of natural sorbents, and this plays a big role when including one or another reagent in technological scheme water purification, then we can assume that it is rational to use highly dispersed minerals as an additive before introducing coagulants in order to more completely remove pathogenic microorganisms from water.[...]
Silty and silty-clayey silts are displaced to the periphery of upwelling zones and are distributed either in the outer part of the shelf or in the lower half of the continental slope. Thus, fine aleurite silts are found in isolated areas in the outer part of the Peruvian shelf (7-10° S). They are 80% composed of quartz grains, the rest are fragments of metamorphic rocks (10%), plagioclases (1%) and potassium feldspars (7%). Silty-clayey silts consist of aggregates of clay minerals with low interference color and disordered texture. Characterized by an abundance of thin mica flakes and plates of hornblende, and in areas of modern volcanism (outskirts of Peru) also volcanic glass.[...]
The negative charge of crystalline clay minerals is independent of pH. Colloids that carry only a negative charge are called acidoids, and those that carry only a positive charge are called bases and.[...]
Clay formation is the process of formation of secondary clay minerals. It can be carried out as a result of the direct on-site transformation of primary minerals into secondary ones under the influence of biochemical and chemical agents, as well as as a result of processes of secondary synthesis from mineralization products of organic residues. Clay formation is facilitated by sufficient profile moisture under conditions of a long period with positive temperatures, as well as intensive processes of biological circulation of substances. In the development of clayification processes in the soil profile, the participation of microorganisms and waste products and decomposition of higher plants is important. Clay formation occurs in the middle part of the profile, where the state of thermal and water regimes is most stable and favorable for clay weathering. On stony-cartilaginous rocks, clay formation is observed from the surface. During claying, silt, iron, aluminum, manganese, phosphorus, magnesium, calcium and other elements accumulate in the soil profile.[...]
A typical desert aerosol consists of 75% clay minerals (35% montmorillonite and 20% each of kaolinite and illite), 10% each of calcite, and 5% each of quartz, potassium nitrate and iron compounds limonite, hematite and magnetite with an admixture of some organic substances . According to line 1a of table. 7.1, the annual production of mineral dust varies widely (0.12-2.00 Gt). The concentration decreases with height, so that mineral dust is observed mainly in the lower half of the troposphere up to altitudes of 3-5 km, and above areas of dust storms - sometimes up to 5-7 km. The size distribution of mineral dust particles usually has two maxima in the ranges of the coarse (mainly silicate) fraction r = 1... 10 µm, which significantly affects the transfer of thermal radiation, and the submicron fraction r[...]
At the same time, depending on the composition of brines and clay minerals, the filtration properties of clays and loams change sharply. When filtering sodium chloride solutions, changes in the filtration properties of sandy-clay deposits compared to fresh water are significantly greater (up to 5-10 times) than when filtering calcium chloride solutions (1.5-2 times). The permeability of montmorillonite clays increases especially sharply (10 times or more) and, to a lesser extent, kaolinite. In addition, the temperature of the filtered water affects the permeability of clays. An increase in temperature from 20 ° C to 30 ° C increases the permeability of montmorillonite clays by 10, sometimes 100 times [Goldberg , Skvortsov, 1986] In general, depending on the composition of clay minerals, their permeability in the temperature range 20-90°C increases by an order of magnitude or more.[...]
The sorption properties of the mineral part of soils are determined by the clay fraction, represented by a mixture of various clay minerals: layered aluminosilicates, oxides and hydroxides of various elements. The ability of clay minerals to stoichiometrically bind metal cations, exchanging them for other cations, is called cation exchange capacity. [...]
The skeleton and plasma of the soil are isolated in thin sections. The skeleton consists of minerals larger than 2 microns - mainly various primary soil minerals; plasma is represented by thin particles less than 2 microns in diameter. It consists of clay minerals, secondary non-silicate oxides of iron and aluminum, humus and, depending on the composition, is divided into clayey, humus-clayey, carbonate-clayey, and ferruginous-clayey. In thin sections, the nature of porosity, aggregation and various new formations are clearly visible, indicating the nature of the soil-forming process.[...]
As was shown above, at a constant pH value, the adsorption capacity of clay minerals decreases in the sequence montmorillonite-illite->kaolinite. In soils with a neutral (pH 7) or alkaline (pH 7-10) reaction between soil particles and the herbicide, only weak van der Waals forces act. Under these conditions, only molecular adsorption is possible. In an acidic environment, the forces of electrostatic interaction begin to manifest themselves, and as a result, in acidic soils, adsorption on the so-called N-clay minerals is much stronger. The amount of adsorption depends on the amount of exchangeable hydrogen ions (or monovalent cations) in the soil. In neutral and especially alkaline environments (pH above 7), for example in calcium clay minerals, herbicides are much less adsorbed. Adding acidic mineral fertilizers to such soils leads to an increase, and lime - to a weakening of their adsorption capacity. [...]
Study on the use of adsorption and adhesive properties of highly dispersed clay minerals and ion exchange capacity polymer materials for water disinfection are not carried out systematically. However, the classification data for water purification, as well as their experimental testing, indicate that such research will improve water treatment methods, and the use of the above materials will be one of the most realistic ways to solve the problem of water disinfection even from the most resistant forms of pathogens of various diseases, and especially viruses.[...]
The use of highly dispersed additives of clay minerals with adsorption properties for water disinfection should be considered a necessary measure in cases where conventional disinfection methods are not effective enough. Since, with increased turbidity of water, pathogenic agents are to a certain extent protected from the destructive effects of radiation, oxidizing agents or heavy metal ions, subsequent disinfection of water requires deep clarification. Hudson's data can serve as an illustration of what has been said. He found that the incidence of infectious hepatitis in US cities was related to the turbidity of the water supplied to the population and the number of bacteria in it. With a water turbidity of 0.15 mg/l, the incidence rate was 3, at 0.3 mg/l - 31, and at 1 mg/l - 130 people for every 100 thousand [...]
Iron ores. Most works on selective flocculation are devoted to the separation of iron oxides from quartz and clay minerals during the beneficiation of iron ores.[...]
Depending on the type of mineral, packages of two or three spruces or sheets are formed. The crystal lattice of minerals consists of many such packages. There are free interpacket spaces between them. There are two main types, the structure of the crystal lattice of clay minerals.[...]
Sandy and sandy loam soils consist of quartz and feldspars, loamy soils are composed of a mixture of primary and secondary minerals, and clayey soils are predominantly composed of secondary clay minerals with an admixture of quartz. Many important physical, physicochemical and chemical properties of the soil depend on the mechanical composition of the soil. The content in soils of iron, calcium, magnesium, potassium, sodium and other nutrients that are included only in the mineral part of the soil, and to some extent also phosphorus, which is found in both the mineral and organic parts of the soil, is determined mainly by their mechanical composition. Heavier clay and loamy soils are richer in nutrients than light sandy and sandy loam soils.[...]
From the previous remarks it is obvious that knowledge of the type of distribution (flaky, structural or dispersed) and the nature of clay minerals is very important for predicting the range of changes in permeability and the existence and distribution of permeability barriers. [...]
The thermal method of fixing microquantities of radioactive isotopes in silicate materials is based on the property of clay minerals to lose their ion-exchange properties as the temperature increases. In bentonite clays, a relatively reliable effect was achieved at 1000 °C. Fixation can also be carried out in carbonate rocks.[...]
Having in an exchangeable state a number of elements that, due to their weak connection with the crystal lattice, are easily absorbed by plants, clay minerals such as montmorillonite at the same time act as a regulator of the soil solution not only in terms of its concentration, but also the diversity of the salt composition.[ .. .]
As materials that provide the necessary adhesion effect, we investigated natural dispersed aluminosilicates - kaolin, bentonites, palygorskite and other clay minerals (Table 47). As a result of the experiments, it turned out that palygorskite and vermiculite have the maximum sorption capacity in relation to coli bacteria, a suspension of which in concentrations of 200-500 mg/l completely precipitates bacteria suspended in water (up to 300,000 individuals/l).[...]
Humins of soil humus, according to modern research, are humic acids of a more simplified structure, which are firmly associated with the mineral part of the soil, with particles of clay minerals of the montmorillonite group. This explains the higher resistance of humins to acids and alkalis. The nitrogen of this humus fraction makes up 20-30% of the total soil nitrogen and is the most tightly bound and resistant to decomposition by microorganisms.[...]
In addition, the absorption of heavy metal cations occurs through isomorphic substitutions and fixation in the lattice. Thus, A11+ of the montmorillonite lattice can be replaced by Fe +, Me2+, Na2+, 2g, Cu2+, Co2+, in vermiculite - by Mg2+, Fe2+, Fe3+, Cr3+, V. Clay minerals are also capable of absorbing anions (molybdate ion, for example), mainly due to the presence of free positive charges in the ionic layer of the crystal lattice.[...]
In geochemical terms, 137C3 can be considered as an analogue of potassium. In nature, the only stable isotope of cesium (its clarke in the earth's crust is 6.5 10 4%) due to isovalent isomorphism is part of the crystal lattice of potassium minerals - micas and feldspars. Radiocesium can bind firmly to the solid phase of soils, penetrating into the interstitial space of clay minerals. The cesium ions fixed in them pass into the soil solution to a much lesser extent. According to Gorina (1976), in gray forest, meadow soils and chernozem, 37Se is distributed between exchangeable (9-15%), non-exchangeable acid-soluble (4-6%) and fixed (81-85%) forms. In light sandy loam soils, the proportion of fixed forms decreases to 60% and the content of exchangeable (28%) and acid-soluble (12%) forms increases. It is believed that the role of organic matter in the sorption of 137C3 is small.[...]
Along the periphery of the bay, especially along the western coast, sand and shell deposits form at the bottom. Hard bedrock, mainly represented by marls, dolomites and mudstones, is exposed near the coast up to an isobath of 5 m. It is known that clay minerals are characterized by sorption properties. The presence of metamorphosed organic matter and humic acids in clay sediments sharply increases the accumulative properties of the latter in relation to metals - copper, lead, zinc, cadmium, nickel - and the toxic non-metal arsenic. Bottom areas with black silts are “traps” for heavy toxic metals. These zones are also favorable for the deposition of material entering the bay with runoff from small rivers, storm drains, sewers and through the mouth of the bay. This process is facilitated by hydrodynamics in the bay, especially during the action of southerly winds, when in the center of cyclonic whirlpools there are relatively low speeds currents compared to the peripheral zone. Thanks to this, we note extensive maximums of heavy metals (Cu - up to 72.4 mg/kg, Zn - up to 77.0 mg/kg, Pb - up to 46.4 mg/kg, Cd - up to 12.0 ■ 10 2 mg/ kg) in the central part of the mainly eastern half of the bay. Areas of elevated metal contents (Cu, Cd, Zn, Pb) are confined to areas of sediment contamination with petroleum products (OP). The greatest pollution of sea water in the NP was observed on the course of ships moving towards the passenger berth, in the area of the passenger berth, and in the ships' roadstead. In the sediments of the bay, three areas of pollution of the NP were noted: passenger and cargo berths, the mouth of the river. Su Aran, center of the bay. Oil pollution also accumulates in fine silt sediments in the center of the bay. According to the classification, sediments are classified as clean soils (NP content up to 100 mg/kg). The main sources of pollution in the NP are maritime cargo and passenger transport, and urban storm drains. The distribution of technogenic organic substances in marine environment bays (PAHs, phenols, surfactants and organochlorine pesticides). The observation results showed that the concentrations of organic substances are observed at background levels.[...]
The mineralogical composition of soddy-podzolic soils is varied and depends mainly on the mechanical composition and properties of the soil-forming rocks. Quartz, feldspars, micas and other primary minerals are found in large fractions of mechanical elements. According to N.I. Gorbunov, in the silty (less than 0.001 mm) fraction of soils formed on moraine and cover loams, the most characteristic highly dispersed minerals are hydromicas, vermiculite, minerals of the montmorillonite group, and non-silicate amorphous sesquioxides. Sometimes there is a small admixture of kaolinite, quartz, and rarely goethite and gibbsite. At the same time, highly dispersed clay minerals and sesquioxides are usually less in the podzolic horizon and more in the illuvial horizon. Soils formed on massively crystalline or well-drained sedimentary rocks are dominated by hydromicas, vermiculite, kaolinite, minerals of the montmorillonite group, and chlorites. Among the accompanying minerals, there are amorphous oxides, quartz.[...]
Ammonification is a process of decomposition of organic substances that occurs with the participation of specific ammonifying microorganisms and leads to the formation of N113 or NH. Ammonium ion can be leached or absorbed in the soil complex or permanently fixed by three-layer clay minerals with an expanding lattice. The content of fixed ammonium in soils varies from 1-2 to 10-12 mmol/100 g of soil. Ammonification is the first stage of mineralization of nitrogen-containing organic compounds.[...]
One of the most important reasons for polymer adsorption on suspended particles is the formation of chemical valence bonds during polymer adsorption. The possibility of the formation of such bonds is indicated during the reaction of carboxyl groups of polyacrylates and hydrolyzed polyacrylamide with clay minerals containing calcium and surface calcium salts. Strong chemical compounds are formed by starch containing esters of phosphoric acid in the presence of Ca, Ag and Zn cations. Finally, this type of reaction includes the irreversible replacement of ion-exchange cations of clay minerals with organic amines: decylamine chloride, hexadecyloxymethylpyridium chloride, etc. We have shown that such a replacement occurs during flocculation of clay suspensions (illite, gumbrine, kaolinite and bentonite) with cationic flocculants B A-2 and VA-3, the molecule of which contains groups of quaternary ammonium bases.[...]
Effective way The fight against radioactive contamination is the fixation of radionuclides with organic matter with the formation of insoluble complexes (chelates). In most soils, an increase in pH and the amount of exchangeable potassium and calcium promotes the sorption of radionuclides (for example, strontium). Clay minerals are good at fixing radionuclides such as strontium and cesium.[...]
Clay fractions ([...]
Exchange absorption (sorption) of anions is pronounced in acidic soils rich in colloidal forms of sesquioxides or other, for example organic, ampholitoids. Such soils are expected to have positively charged surfaces. V. M. Klechkovsky and N. V. Kashirkina showed the possibility of reversible exchange of hydroxyls of some clay minerals for phosphate ions. On soils rich in sesquioxides, the possibility of exchange absorption of anions C1, N0, BO-, etc., along with cation exchange processes, has been experimentally shown. However, for many polyvalent anions, the experimental study of exchange sorption is difficult due to the simultaneously occurring chemical non-exchange absorption of these ions.[. ..]
The predominant climatic factors that control the type of sediment on the shelf are temperature and precipitation (Fig. 9.5). The most significant changes in these parameters coincide with the most noticeable latitudinal variations in the nature of shelf sediments. In polar climates, for example, silt deposits contain few clay minerals, the characteristic component of the clay fraction being chlorite, and extensive gravel deposits are adjacent to land glaciers. In the rainy tropical climate However, abundant silts contain a large proportion of clay minerals; Kaolin is often abundant near small rivers; quartz predominates in coarse-grained sediments. In hot, dry climates, windblown sand and silt may predominate. In the most temperate climates, it is impossible to distinguish distinct types of precipitation.[...]
The most important nonspecific nitrogen-containing substances that are found in soils in a free state are proteins. In addition to proteins, soils contain amino acids, amino sugars, nucleic acids, chlorophyll, and amines. Most of these nitrogen-containing substances, which are not part of humic substances, are adsorbed on the surface of clay minerals or form insoluble compounds with the mineral components of soils. Under the influence of the enzymatic activity of microorganisms, proteins are broken down into less complex components, easily humified and mineralized.[...]
Thus, in the Aptian in the Central Atlantic, margins appeared that, in their appearance and facies spectrum of sediments, were close to the modern margins of peneplainized areas of cratons. The same margins arose along the periphery of the South Atlantic basin (the modern Argentine and Cape basins). The lower horizons penetrated by these wells are dominated by illite (30-50%) and kaolinite (20-45%) with an admixture of chlorite and mixed-layer formations (the latter is dominated by the vermiculite phase). The same association is recorded in deposits of Early Aptian age. However, up the section the content of montmorillonite gradually increases in it (from 5 to 85%). It is interesting that palygorskite is found as an impurity in these same layers. Such a change in minerals along the section may indicate tectonic activation that captured transition zones in the first half of the Early Cretaceous, with subsequent leveling of the relief and the formation of vast coastal plains, in the depths of which there were residual uplifts with weathering crusts formed on them. Thus, the study of clay minerals in sediments of passive margins makes it possible to reconstruct not only the climate of the past, but also the tectonic state of a particular area.[...]
With increasing temperature, the solubility of hydrocarbons increases. But the role of temperature is manifested not only in increasing the solubility of hydrocarbons, but also in reducing the adsorption capacity of rocks. Thus, according to U. M. Dau, with an increase in temperature from 32 to 38 ° C, the adsorption capacity of adsorbents for C2 - C6 hydrocarbons decreases by 25%. The adsorption capacity of rocks also decreases as a result of the restructuring of clay minerals: the adsorption capacity of hydromicas is reduced by 3-4 times compared to the adsorption capacity of montmorillonite.[...]
The amount of exchangeable bases is high - up to 50 mEq, with exchangeable magnesium making up 25-50% of the amount and its content increases with depth. Exchangeable sodium is usually low - up to 5% of the amount. In terms of humus content in the upper horizon (3-8%), dark drained soils are close to chernozems, CHA/CFA is equal to 1.5-2. Among humic acids, the content of the fraction associated with clay minerals and stable sesquioxides is relatively high. In the upper layers there may be an increased content of brown humic acids. [...]
Heavy metals in the soil undergo various transformations: fixation by humic substances, which occurs as a result of the formation of HM salts with organic acids, adsorption of ions on the surface of colloidal systems or complexation with humic acids. Some part of HM ions is adsorbed on the surface of mineral particles. It is also possible for them to penetrate into the interplanar space of clay minerals or isomorphically replace ions of other elements in the crystal lattice.[...]
The mobility of molybdenum in soils, its availability to plants and the effectiveness of molybdenum fertilizers are determined by a number of factors, the most important of which is the reaction of the environment. The alkaline reaction enhances the mobility of molybdenum, while at the same time, in an acidic environment, it transforms into compounds that are less mobile and difficult to reach for plants. In acidic soils, molybdenum is associated with iron, aluminum, manganese, and clay minerals in the soil. When the acidic environment is neutralized, which is achieved by liming, molybdenum transforms into forms that are more digestible by plants. Moreover, the less mobile molybdenum is contained in soils, the higher the efficiency of molybdenum fertilizers.[...]
When microwave heating occurs, a significant transformation of the chemical and mineral composition of soils occurs. Thus, in the temperature range of 100-300 °C, soil dehydration occurs with the loss of not only free, but also bound water. At the same time, soil shrinkage develops and the proportion of condensation structural bonds increases. At a temperature of 350-600 °C, organic combustion and destruction of low-temperature pollutants occur, and sulfides are oxidized (350-500 °C). In the range of 450-800 °C, hydroxyl groups are removed from clay minerals and contaminants with OH groups. At the same time, irreversible phase contacts are formed in the soil, the proportion of which in the soil increases with increasing temperature. In the range of 400-900 °C, carbonates dissociate with the formation of oxides (CaO), which have hydraulic binding properties and increase soil pH. At temperatures above 1000 °C, melting and formation of high-temperature mineral phases in the soil occur.[...]
At any given time only small area the cone receives sediment. In other places, in areas devoid of sediment, post-sedimentation processes take place, which can last hundreds of years and significantly transform the features of the sedimentary origin itself. The main post-sedimentation agents are weathering, runoff atmospheric precipitation and wind. Chemically unstable clasts continue to break down, and the products of this process are washed away either into the underlying sediments or along the surface of the fan into more distal settings. Some of the fine-grained material can apparently be transported by wind deflation, with wind-blown sands accumulating in the form of dunes, most often in the lower parts of the fan surface. Precipitation lead to the formation of gullies and ravines, and in the areas between them a “desert pavement” is formed from angular fragments closely pressed together, often covered with a desert tan. Such “pavements” protect the fan surface from further deflation, and large clasts usually rest on a layer of silt. In semiarid settings, fan sediments are often colored red as weathering breaks down ferromagnesian minerals and biotite to form hematite and clay minerals. Such transformations take millennia and are facilitated by alternating periods of wetting and drying.
And the physical, chemical, mechanical and other properties that determine them.
Clay minerals are a product of weathering mainly of aluminosilicates and silicates of igneous and metamorphic rocks on the surface. During the weathering process, clay minerals undergo stage-by-stage transformations of structure and chemical composition depending on changes in the physicochemical conditions of the weathering and sedimentation environment. The particle sizes of clay minerals in clays for the most part do not exceed 0.01 mm. According to their crystal structure, clay minerals belong to layered or pseudolayered silicates.
High specific surface area, isomorphic substitutions, abundance of crystal lattice chips and uncompensated charges give clay minerals cation exchange ability. They are also capable of chemically binding water.
The composition of minerals includes layers consisting of silicon-oxygen tetrahedra and aluminum-hydroxyl octahedra; these layers are combined into elementary packages, the totality of which forms a mineral particle. Based on the set of layers in the package, several groups of clay minerals are distinguished:
- A group of kaolinite (kaolinite, halloysite) with a package consisting of one layer of octahedra and one layer of tetrahedra. The packages are firmly connected to each other and fit tightly to each other, as a result of which water molecules and metal cations cannot enter the interpacket space and the mineral does not swell in water, and also has a low cation exchange capacity (CEC).
- Montmorillonite group or smectite group (montmorillonite, nontronite, beidelite, etc.) with a three-layer tetrahedron-octahedron-tetrahedron package. The connection between the packages is weak, water penetrates there, which is why the mineral swells greatly. It has a high CEC (up to 80-120 mEq per 100 g).
- A group of hydromicas (hydrobiotite, hydromuscovite, etc.) also with a three-layer package, but with a strong bond between them. They practically do not absorb water and do not swell in it. They are distinguished by their high potassium content, since its ionic radius allows it to enter the voids of the mineral structure.
- Chlorite group with a four-layer swelling structure.
- A group of mixed-layer minerals with alternating packets of different types. They are called illite-montmorillonite, vermiculite-chlorite, etc., the properties vary greatly.
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Literature
- Ginzburg I.I., Rukavishnikova I.A., Minerals of the ancient weathering crust of the Urals, M., 1951;
- X-ray methods of studying and structure of clay minerals, trans. from English, M., 1965.
Excerpt characterizing Clay minerals
The comrade soldiers walking next to Pierre did not look back, just like him, at the place from which a shot was heard and then the howl of a dog; but a stern expression lay on all faces.The depot, the prisoners, and the marshal's convoy stopped in the village of Shamsheva. Everything huddled around the fires. Pierre went to the fire, ate the roasted horse meat, lay down with his back to the fire and immediately fell asleep. He slept again the same sleep that he slept in Mozhaisk after Borodin.
Again the events of reality were combined with dreams, and again someone, whether he himself or someone else, told him thoughts, and even the same thoughts that were spoken to him in Mozhaisk.
“Life is everything. Life is God. Everything moves and moves, and this movement is God. And as long as there is life, there is the pleasure of self-consciousness of the deity. Love life, love God. It is most difficult and most blissful to love this life in one’s suffering, in the innocence of suffering.”
“Karataev” - Pierre remembered.
And suddenly Pierre introduced himself to a living, long-forgotten, gentle old teacher who taught Pierre geography in Switzerland. “Wait,” said the old man. And he showed Pierre the globe. This globe was a living, oscillating ball that had no dimensions. The entire surface of the ball consisted of drops tightly compressed together. And these drops all moved, moved and then merged from several into one, then from one they were divided into many. Each drop sought to spread out, to capture the greatest possible space, but others, striving for the same thing, compressed it, sometimes destroyed it, sometimes merged with it.
“This is life,” said the old teacher.
“How simple and clear this is,” thought Pierre. “How could I not know this before?”
- There is God in the middle, and every drop strives to expand so that largest sizes reflect it. And it grows, merges, and shrinks, and is destroyed on the surface, goes into the depths and floats up again. Here he is, Karataev, overflowing and disappearing. “Vous avez compris, mon enfant, [You understand.],” said the teacher.
“Vous avez compris, sacre nom, [You understand, damn you.],” a voice shouted, and Pierre woke up.
He rose and sat down. A Frenchman, who had just pushed aside a Russian soldier, sat squatting by the fire and was frying meat that had been put on a ramrod. Veiny, rolled-up, hairy, red hands with short fingers deftly turned the ramrod. A brown gloomy face with frowning eyebrows was clearly visible in the light of the coals.
“Ca lui est bien egal,” he grumbled, quickly turning to the soldier standing behind him. -...brigand. Va! [He doesn't care... a robber, really!]
And the soldier, twirling the ramrod, looked gloomily at Pierre. Pierre turned away, peering into the shadows. One Russian soldier, a prisoner, the one who had been pushed away by the Frenchman, sat by the fire and ruffled something with his hand. Looking closer, Pierre recognized a purple dog, which, wagging its tail, was sitting next to the soldier.
