Plan.

Option number 6.

1. Classification of minerals and conditions of their formation: the main rock-forming minerals of exogenous and endogenous origin.

2. Glaciers, their geological role, distribution. Rocks formed as a result of the work of glaciers during the Ice Age.

3. Geotechnical research for industrial and civil construction.

4. Laboratory methods for determining the deformation and strength properties of soils.

5. Structure, texture, material composition of chemical and biochemical sedimentary rocks.

6. Inflow of pressure water into a perfect well.

Introduction.

Geology is a complex of sciences about composition and structure. The history of the development of the Earth, movements of the earth's crust and the placement of minerals in the bowels of the Earth. The main object of study, based on the practical tasks of man, is the earth's crust.

In recent decades, engineering geology has received special development - a science that studies the properties of rocks (soils), natural geological and technogenic-geological (engineering-geological) processes in the upper horizons of the earth's crust in connection with human construction activities.

The main goal of engineering geology is to study the natural geological situation of an area before the start of construction, as well as to predict the changes that will occur in the geological environment, and primarily in rocks, during the construction process and during the operation of structures. In modern conditions, not a single building or structure can be designed, constructed and reliably operated without reliable and complete engineering and geological materials.

1. Classification of minerals and conditions of their formation: the main rock-forming minerals of exogenous and endogenous origin.

Mineral– a natural body with a certain chemical composition and crystalline structure, formed as a result of natural physical and chemical processes and being an integral part of the earth’s crust, rocks, ores, and meteorites. The science of mineralogy is the study of minerals.

The earth's crust contains more than 7,000 minerals and their varieties. Most of them are rare and only a little more than 100 minerals are found frequently and in fairly large quantities and are part of certain rocks. Such minerals are called rock-forming minerals.

Origin of minerals. The conditions under which minerals are formed in nature are very diverse and complex. There are three main processes of mineral formation: endogenous, exogenous and metamorphic.

Endogenous process is connected with the internal forces of the Earth and manifests itself in its depths. Minerals are formed from magma - a silicate fiery liquid melt. In this way, for example, quartz and various silicates are formed. Endogenous minerals are usually dense, with great hardness, resistant to water, acids, and alkalis.

Exogenous process characteristic of the surface of the earth's crust. In this process, minerals are formed on land and in the sea. In the first case, their creation is associated with the weathering process, i.e. the destructive effects of water, oxygen, temperature fluctuations on endogenous minerals. In this way, clay minerals (hydromica, kaolinite, etc.), various ferruginous compounds (sulfides, oxides of chemical precipitation from aqueous solutions (halite, sylvite, etc.) are formed. In an exogenous process, a number of minerals are also formed due to the vital activity of various organisms (opal and etc.).

Exogenous minerals vary in properties. In most cases, they have low hardness and actively interact with water or dissolve in it.

Metamorphic process. Under the influence of high temperatures and pressures, as well as magmatic gases and water at some depth in the earth's crust, the transformation of minerals that were previously formed in exogenous processes occurs. Minerals change their original state, recrystallize, acquire density and strength. This is how many silicate minerals are formed (hornblende, actinolite, etc.).

Classification of minerals. There are many classifications of minerals. The most widely used classification is based on chemical composition and crystal structure. Substances of the same chemical type often have a similar structure, so minerals are first divided into classes based on chemical composition, and then into subclasses based on structural characteristics.

All minerals are divided into 10 classes.

Silicates- the most numerous class, including up to 800 minerals, which are the main part of most igneous and metamorphic rocks. Among silicates, there are groups of minerals characterized by some common composition and structure - feldspars, pyroxenes, amphiboles, micas, as well as olivine, talc, chlorites and clay minerals. All of them are aluminosilicates in composition.

Carbonates. These include more than 80 minerals. The most common are calcite, magnetism, and dolomite. The origin is mainly exogenous and associated with aqueous solutions. In contact with water, they slightly reduce their mechanical strength, although weakly, but they dissolve in water and are destroyed in acids.

Oxides and hydroxides. These two classes combine about 200 minerals, accounting for up to 17% of the total mass of the earth's crust. The most common are quartz, opal and limonite.

Sulfides contain up to 200 minerals. A typical representative is pyrite. Sulfides are destroyed in the weathering zone, so their admixture reduces the quality of building materials.

Sulfates. This class includes up to 260 minerals, the origin of which is associated with aqueous solutions. They are characterized by low hardness and light color. Relatively well soluble in water. The most common are gypsum and anhydrite. Upon contact with water, anhydrite turns into gypsum, increasing in volume up to 33%.

Halides contain about 100 minerals. The origin is mainly associated with aqueous solutions. The most widespread is halite. It can be a component of sedimentary rocks and easily dissolves in water.

Minerals of the phosphate, tungstate, and native element classes are much less common than others.

2. Glaciers, their geological role, distribution. Rocks formed as a result of the work of glaciers during the Ice Age.

Geological evidence suggests that in ancient times the glaciation of the Earth was significant. Over the past 500-600 thousand years, several large glaciations have occurred in Europe. Glaciers advanced from the Scandinavian region.

Currently, ice covers 10% of the land surface, 98.5% of the glacial surface is in the polar regions and only 1.5% is in high mountains. There are three types of glaciers: mountain, plateau and continental.

Mountain glaciers are formed high in the mountains and are located either on the peaks or in gorges, depressions, and various depressions. Such glaciers are found in the Caucasus, Urals, etc.

Ice is formed due to the recrystallization of snow. It has the ability to flow plastically, forming flows in the form of tongues. The movement of glaciers down slopes is limited by the altitude where solar heat is sufficient to completely melt the ice. For the Caucasus, for example, this height is 2700 m in the west, 3600 m in the east. The speed of movement of mountain glaciers is different. In the Caucasus, for example, it is 0.03-0.35 m/day, in the Pamirs – 1-4 m/day.

Glaciers of the plateaus formed in mountains with flat tops. The ice lies in an indivisible continuous mass. Glaciers in the form of tongues descend from it through the gorges. This type of glacier, in particular, is now located on the Scandinavian Peninsula.

Continental glaciers common in Greenland, Spitsbergen, Antarctica and other places where the modern era of glaciations is currently taking place. The ice lies in a continuous layer, thousands of meters thick.

The geological activity of ice is great and is determined mainly by its movement, despite the fact that the speed of ice flow is approximately 10,000 times slower than water in rivers under the same conditions.

Construction properties of glacial deposits. Moraine (coarse, heterogeneous, non-layered clastic materials) and fluvioglacial (fluvio-glacial) deposits are a reliable basis for structures of various types. Boulder loams and clays, which have experienced the pressure of thick layers of ice, are in a dense state and in some cases even over-compacted. The porosity of boulder loams does not exceed 25-30%. On boulder loams and clays, buildings and structures experience low settlement. These soils are weakly permeable and often serve as a waterproof barrier for groundwater.

Almost all types of moraine deposits have such high strength properties.

From a construction point of view, fluvioglacial deposits, although inferior in strength to moraine clayey soils, are a reliable foundation. For this purpose, various sandy, gravelly and clayey deposits of eskers and outwash are successfully used. Some exceptions are cover loams and band clays. Covering loams get wet easily. Band clays are quite dense, slightly permeable to water, but can be fluid under conditions of saturation with water.

Glacial deposits are successfully used as building materials (stone, sand, clay); The sands of eskers, kames and outwash are suitable for the construction of embankments and for the production of concrete. Boulders are a good building stone. There are examples of the use of boulders to make monolithic pedestals for monuments.

3. Geotechnical research for industrial and civil construction.

The main task of engineering-geological research for industrial and civil construction is to obtain information about the engineering-geological conditions of the territory, which include: relief, rocks and their properties, groundwater, geological and engineering-geological processes and phenomena, as well as forecasting changes in these conditions under the influence of human engineering activities.

Engineering geological studies are carried out sequentially,

in accordance with the design stage. The detail of research increases during the transition from one stage to another, and the methods of engineering and geological research also change.

At the initial stage of engineering surveys, the main type of engineering-geological research is engineering-geological survey, which makes it possible to assess engineering-geological conditions in a short time and at low cost.

During engineering-geological survey, rocks, their occurrence conditions, relief, groundwater, geological and engineering-geological processes are identified, studied and traced in the study area and depicted on an engineering-geological map.

It is important to understand that the composition and volume of engineering-geological research depends on the complexity of engineering-geological conditions, the design stage, the degree of exploration of the area and other factors.

Attention should be paid to the significant complexity of engineering-geological research in areas of karst development, landslides, buried valleys, where all research is carried out to a greater depth than during research in areas with more favorable engineering-geological conditions.

4. Laboratory methods for determining the deformation and strength properties of soils.

Strength soil is estimated by the maximum load applied to it at the moment of destruction (loss of continuity). This characteristic is called tensile strength R c MPa, or temporary compressive strength.

The strength of soils is affected by:

    mineral composition

    nature of structural connections

    fracturing

    degree of weathering

    degree of softening in water, etc.

For non-rocky soils, another important strength characteristic is shear strength. Determining this indicator is necessary to calculate the stability of the foundations, i.e. bearing capacity, as well as for assessing the stability of soils in the slopes of construction pits, calculating soil pressure on retaining walls, etc.

Deformation properties characterize the behavior of soils under loads that do not exceed critical loads and do not lead to destruction. The deformability of soils depends both on the resistance and compliance of structural bonds, porosity, and on the ability of the materials composing them to deform. The deformation properties of soils are assessed by the deformation modulus E, MPa.

Soils determine the stability of buildings and structures erected on them, therefore it is necessary to correctly determine the characteristics that determine the strength and stability of soils during their interaction with construction objects.

Soil samples for laboratory research are selected from soil layers in pits in boreholes that are located on construction sites.

Soil samples are delivered to the laboratory in the form of monoliths or loose samples. Monoliths are samples of soil with an undisturbed structure. Such monoliths are selected in rocky and cohesive (silty-clayey) soils. The dimensions of the monoliths must be no less than the established standards. Thus, to determine the compressibility of soil, samples taken in pits must have dimensions of 20 × 20 × 20 cm. In monoliths of silty clay soils, natural moisture must be preserved. This is achieved by creating a waterproof paraffin or wax shell on their surface. In loose soils (sand, gravel), samples are taken in the form of samples of a certain mass. Thus, to carry out granulometric analysis of sand, it is necessary to have a sample of at least 0.5 kg.

In laboratory conditions, all physical and mechanical properties can be determined. Each characteristic of these properties is determined according to GOST, for example, natural moisture and soil density - GOST 5180-84, tensile strength - GOST 17245-79, granulometric (grain) and microaggregate composition - GOT 12536-79, etc.

Laboratory research today remains the main type of determination of the physical and mechanical properties of soils. A number of characteristics, for example, natural humidity, density of soil particles and some others are determined only in laboratory conditions and with fairly high accuracy. At the same time, laboratory soil studies have their drawbacks:

    they are quite labor-intensive and time-consuming;

    the results of individual analyzes, for example, determination of the modulus of total deformation, do not give sufficiently accurate results, which is due to improper selection of monoliths, improper storage, and low qualifications of the analysis performer;

    Determining the properties of a soil mass based on the results of analyzes of a small number of samples does not allow one to obtain a correct idea of ​​its properties as a whole.

This is due to the fact that soils of the same type, even within the same massif, still have known differences in their properties.

5. Structure, texture, material composition of chemical and biochemical sedimentary rocks.

Rocks are natural mineral aggregates that are “born” in the earth’s crust.

According to their origin, they are divided into three types: igneous, sedimentary and metamorphic. In the earth's crust, igneous and metamorphic rocks occupy 95% of its total mass. Sedimentary rocks are located directly on the surface of the Earth, covering in most cases igneous and metamorphic rocks.

Sedimentary rocks. Any rock located on the earth's surface is subject to weathering, i.e. the destructive effects of water, temperature fluctuations, etc. As a result, even the most massive, durable igneous rocks are gradually destroyed, forming fragments of various sizes and disintegrating into the smallest particles.

Destruction products are transported by wind, water and, at a certain stage of transport, are deposited, forming loose accumulations or sediments. Accumulation occurs at the bottom of rivers, seas, oceans and on the surface of the land. From loose accumulations (sediments) various sedimentary rocks are formed over time.

Sedimentary rocks make up the uppermost layers of the earth's crust, covering rocks of igneous and metamorphic origin with a kind of cover. Despite the fact that sedimentary rocks make up only 5% of the earth's crust, 75% of the earth's surface is covered with these rocks, and therefore construction is carried out mainly on sedimentary rocks. Engineering geology pays the greatest attention to these rocks.

Sedimentary rocks are usually divided into three main groups:

1) clastic;

2) chemical origin (chemogenic);

3) organogenic, resulting from the vital activity of organisms.

This division is somewhat arbitrary, since many rocks are of mixed origin, for example, some limestones contain material of an organogenic, chemical and clastic nature.

Chemogenic rocks are formed as a result of the precipitation of their aqueous solutions of chemical precipitation. This process occurs in the waters of the seas, continental drying basins, salty springs, etc. These rocks include various limestones, calcareous tuff, dolomite, anhydrite, gypsum, rock salt, etc. A common feature of these rocks is their solubility in water and fracturing.

The most common rocks are limestones, which in their origin can also be clastic or organogenic.

Organogenic (biochemogenic) rocks are formed as a result of the accumulation and transformation of animal and plant remains, are characterized by significant porosity, many dissolve in water, and are highly compressible. Organogenic rocks include limestone-shell rock and diatomite.

6. Inflow of pressure water into a perfect well.

The water located in the upper part of the earth's crust is called groundwater. The science of groundwater, its origin, conditions of occurrence, laws of movement, physical and chemical properties, connections with atmospheric and surface waters is called hydrogeology.

There are several classifications of groundwater, but there are two main ones. Groundwater is divided according to the nature of its use and the conditions of occurrence in the earth's crust. The first includes household and drinking water, technical, industrial, mineral, thermal. The latter include: perched water, groundwater and interstratal water, as well as water from cracks, karst, and permafrost. For engineering and geological purposes, it is advisable to classify groundwater according to hydraulic criteria - free-flow and pressure.

Interlayer pressure waters. These waters are located in aquifers between aquitards. They can be non-pressure and pressure (artesian).

Interstratal non-pressure waters are relatively rare. They are associated with horizontal aquifers filled with water completely or partially.

Pressure (artesian) waters are associated with the occurrence of aquifers in the form of synclines and monoclines. The area of ​​distribution of confined aquifers is called an artesian basin.

Inflow of pressure water to water intake structures. Water intakes are structures with the help of which groundwater is captured (withdrawn) for water supply, drained from the construction site or simply for the purpose of lowering groundwater levels. There are different types of underground water intake structures: vertical, horizontal, radial.

Vertical water intakes include boreholes and shaft wells, horizontal ones include trenches, galleries, adits, and radial water intakes include drainage wells with water receiving filter beams. The type of structure for underground water intake is selected on the basis of a technical and economic calculation, based on the depth of the aquifer, its thickness, the lithological composition of the aquifer and the planned water intake capacity.

Water intakes consisting of one well, well, etc. are called single, and those consisting of several are called group.

Water intake structures that tap the aquifer to its full capacity are perfect, and those that do not tap the aquifer to its full capacity are imperfect.

The removal of groundwater from construction sites or the reduction of their levels can be carried out temporarily, only for the period of construction work or for almost the entire period of operation of the facility. Temporary water removal (or lowering the level) is called construction water intake, and in the second case - drainage.

Water intake wells. Wells and trenches, the bottom of which reaches aquicludes, are called perfect; if the bottom is located above the aquiclude, then imperfect. The water level in the well before pumping is called static, and the level reduced during pumping is called dynamic.

If water is not pumped out of the well, then its level is in the same position as the surface of the ground flow. When water is pumped out, a depression funnel appears and the water level in the well decreases. The productivity of the well is determined by the flow rate. The flow rate of a well is understood as the amount of water it can produce per unit of time. When pumping water in an amount greater than the flow rate, i.e. more than what flows into the well from the aquifer per unit time, the level drops sharply. The well may remain without water for some time.

The influx of water (flow rate) to a perfect well is determined by the formula

Q = π k f [H 2 -h 2 )/lnR-lnr]

Where r– radius of the well, m.

In an imperfect well, water enters through its walls and bottom. This complicates the calculation of inflow. The flow rate of such wells is less than the flow rate of perfect wells. When pumping, water enters the well only from a part of the aquifer, which is called the active zone N 0 . The depth of the active zone is taken to be 4/3 of the height of the water column in the well before pumping. These provisions allow the flow rate for an imperfect well to be calculated using the Dupuis formula, as interpreted by Parker:

Q = 1.36 k f [H 2 -h 2 )/lnR-lnr]

A well releases water in the volume of its maximum flow only if neighboring wells are located from it at a distance of at least two radii of influence.

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    • Currently, ~3000 minerals are known and their number is increasing every year. How to navigate this large and diverse world of minerals? To do this, scientists group or systematize them based on certain characteristics. That is, they carry out classification. In mineralogy there have been attempts to create a classification based on different signs: for example, by hardness, shine or cleavage; according to the conditions of education or genesis. But there are minerals that can be formed completely in different conditions. Since the middle of the last century, minerals began to be classified according to their chemical composition - according to the dominant anion or anionic group. But only after the advent of X-ray diffraction analysis and the determination of the internal structure of minerals with its help, it became possible to establish a close connection between the chemical composition of a mineral and its crystal lattice. This discovery laid the foundation for the principle of crystallochemical classification of minerals. This was first done by scientists Bragg and Goldschmidt for silicates.

    In this classification, the basic unit is taken to be a mineral species that has a certain crystalline structure and a certain stable chemical composition. The mineral type can have varieties. A variety is understood as minerals of the same type that differ from each other in some way physical sign, for example, the color of the mineral quartz comes in numerous varieties (black - morion, transparent - rock crystal, purple - amethyst).

    During the process of mineral formation, minerals of the same mineral species may differ from each other in appearance - crystal size or shape. In this case, each mineral of one mineral species is called a mineral individual.

    Existing classifications group mineral species into classes or groups. Their number varies among different authors as the classification improves and new data on mineral species are obtained. We will look at eight classes:

    Characteristics of minerals by class

    1. Native

    2. Sulfides

    3. Oxides and hydroxides

    4. Halides

    5. Carbonates

    6. Sulfates

    7. Phosphates

    8. Silicates

    1. Native elements (minerals).

    This class includes minerals consisting of one chemical element and named after this element. For example: native gold, sulfur, etc. All of them are divided into two groups: metals and non-metals. The first group includes native Au, Ag, Cu, Pt, Fe and some others, the second - As, Bi, S and C (diamond and graphite).

    Genesis - mainly formed during endogenous processes in intrusive rocks and quartz veins, S - during volcanism. During exogenous processes, rocks are destroyed, native minerals are released (due to their resistance to physical and chemical influences) and their concentration in places favorable for this. Thus, placers of gold, platinum and diamond can be formed.

    Application in the national economy:

    1 - jewelry production and foreign exchange reserves (Au, Pt, Ag, diamonds);

    2 - religious objects and utensils (Au, Ag),

    3 - radio electronics (Au, Ag, Cu), nuclear, chemical industry, medicine, cutting tools - diamond;

    4 - agriculture - sulfur.

    II. Sulfides are salts of hydrosulfide acid.

    They are divided into simple ones with the general formula A m X p and sulfosalts - A m B n X p, where -

    A is a metal atom, B is atoms of metals and metalloids, X is sulfur atoms.

    (Pb, Cu, Fe, etc.) (Bi, Sb, As, Sn)

    Sulfides crystallize in different systems - cubic, hexagonal, orthorhombic, etc. Compared to native ones, they have a wider composition of element cations. Hence there is a greater variety of mineral species and a wider range of the same property.

    Common properties for sulfides are metallic luster, low hardness (up to 4), gray and dark colors, and medium density.

    At the same time, among sulfides there are differences in such properties as cleavage, hardness, and density. For example:

    Sulfides are the main source of non-ferrous metal ores, and due to the admixtures of rare and noble metals, the value of their use increases.

    Genesis - various endogenous and exogenous processes.

    III. Oxides and hydroxides - represent one of the most common classes with more than 150 mineral species in which metal atoms or cations form compounds with oxygen or a hydroxyl group (OH). This is expressed by the general formula AX or ABX - where X is the oxygen atoms or hydroxyl group. The most widely represented oxides are Si, Fe, Al, Ti, and Sn. Some of them also form the hydroxide form. A feature of most hydroxides is a decrease in property values ​​compared to the oxide form of the same metal atom. A striking example of p is the oxide and hydroxide forms of Al.

    Based on their chemical composition and luster, oxides can be divided into metallic and nonmetallic. The first group is characterized by medium hardness, dark colors (black, gray, brown), and medium density. An example is the minerals hematite and cassiterite. The second group is characterized by low density, high hardness 7-9, transparency, a wide range of colors, and lack of cleavage. Example p - minerals quartz, corundum.

    In the national economy, oxides and hydroxides are most widely used to produce Fe, Mn, Al, Sn. Transparent, crystalline varieties of corundum (sapphire and ruby) and quartz (amethyst, rock crystal, etc.) are used as precious and semi-precious stones.

    Genesis - during endogenous and exogenous processes.

    IV. Halides. The most widespread are fluorides and chlorides - compounds of metal cations with monovalent fluorine and chlorine.

    Fluorides are light-colored minerals of medium density and hardness. Representative is fluorite CaF2. The chlorides are the minerals halite and selvite (NaCl and KCl).

    The common features of halogens are low hardness, crystallization in the cubic system, perfect cleavage, a wide range of colors, and transparency. Special properties have halite and sylvite - salty and bitter-salty taste.

    Fluorides and chlorides differ in their genesis. Fluorite is a product of endogenous processes (hydrothermal), while halite and sylvite are formed under exogenous conditions due to precipitation during evaporation in water bodies.

    In the national economy, fluorite is used in optics, metallurgy, and for the production of hydrofluoric acid. Halite and sylvite are used in the chemical and food industries, medicine and agriculture, photo business.

    V. Carbonates - salts of carbonic acid, general formula ACO3 - where A - Ca, Mg, Fe, etc.

    General properties: a - crystallizes in rhombic and trigonal systems (good crystalline forms and rhombic cleavage); low hardness 3-4, predominantly light color, reaction with acids (HCl and HNO3) with the release of carbon dioxide.

    The most common are: calcite CaCO3, magnesite Mg CO3, dolomite CaMg (CO3) 2, siderite Fe CO3.

    Carbonates with hydroxyl group (OH):

    Malachite Cu2 CO3 (OH) 2 - green color and reaction with NS l,

    Azurite Cu3 (CO3) 2 (OH) 2 - Blue colour, transparent in crystals.

    The genesis of carbonates is diverse - sedimentary (chemical and biogenic), hydrothermal, metamorphic.

    These are rock-forming minerals of sedimentary rocks (limestones, dolomites, etc.) and metamorphic ones - marble, skarns. They are used in construction, optics, metallurgy, and as fertilizers. Malachite is used as an ornamental stone. Large accumulations of magnesite and siderite are a source of iron and magnesium.

    VI. Sulfates are salts of sulfuric acid, i.e. have SO4 radical. The most common and well-known sulfates are Ca, Ba, Sr, Pb. Their common properties are crystallization in monoclinic and orthorhombic systems, light color, low hardness, glassy luster, and perfect cleavage.

    Minerals: gypsum CaSO4 *2H2O, anhydrite CaSO4, barite BaSO4 (high density), celestine SrSO4.

    They are formed under exogenous conditions, often together with halogens. Some sulfates (barite, celestine) are of hydrothermal origin.

    Application - construction, agriculture, medicine, chemical industry.

    IIV. Phosphates are salts of phosphoric acid, i.e. containing PO4.

    The number of mineral species is small; we will consider the mineral apatite Ca(PO4) 3 (F, Cl, OH). It forms crystalline and granular aggregates, hardness 5, hexagonal system, imperfect cleavage, green-blue color. Contains impurities of strontium, yttrium, rare earth elements.

    Genesis is magmatic and sedimentary, where it forms phosphorite when mixed with clay particles.

    Application - agricultural raw materials, chemical production and in ceramic products.

    VIII. Silicates are the most common and diverse class of minerals (up to 800 species). The systematics of silicates is based on the silicon-oxygen tetrahedron -4. Depending on the structure they form when combined with each other, all silicates are divided into:

    island, layer, strip, chain and frame.

    Island silicates - in them the connection between isolated tetrahedra is carried out through cations. This group includes minerals: olivine, topaz, garnets, beryl, tourmaline.

    Layer silicates represent continuous layers, where the tetrahedra are connected by oxygen ions, and the connection between the layers is through cations. Therefore, they have a common radical in formula 4. This group combines mica minerals: biotite, talc, muscovite, serpentine.

    Chain and ribbon - tetrahedra form single or double chains (ribbons). Chain - have a common radical 4- and include a group of pyroxenes.

    Ribbon silicates with radical 6 - combine minerals of the amphibole group.

    Framework silicates - in them, tetrahedra are connected to each other by all oxygen atoms, forming a framework with a radical. This group includes feldspars and plagioclases. Feldspars combine minerals with Na and K cations. These minerals are microcline and orthoclase. Plagioclases contain Ca and Na as cations, and the ratio between these elements is not constant. Therefore, plagioclases are an isomorphic series of minerals:

    albite - oligoclase - andesine - labradorite - bytownite - anorthite. From albite to anorthite the Ca content increases.

    The composition of cations in silicates most often contains: Mg, Fe, Mn, Al, Ti, Ca, K, Na, Be, less often Zr, Cr, B, Zn, rare and radioactive elements. It should be noted that part of the silicon in tetrahedra can be replaced by Al, and then we classify the minerals as aluminosilicates.

    The complex chemical composition and diversity of the crystal structure combine to produce a wide range of physical properties. Even using the Mohs scale as an example, it can be seen that the hardness of silicates ranges from 1 to 9.

    Cleavage varies from very perfect to imperfect. There is nothing to say about coloring - the widest range of colors and shades.

    At the same time, within each structural group the properties are similar and there is always one or two characteristics by which a mineral can be identified. For example, mica is determined by its cleavage and low hardness.

    Silicates are often grouped by color - dark-colored, light-colored. This is especially widely applied to silicates - rock-forming minerals.

    Silicates are formed mainly during the formation of igneous and metamorphic rocks in endogenous processes. A large group of clay minerals (kaolin, etc.) is formed under exogenous conditions during the weathering of silicate rocks.

    Many silicates are minerals and are used in the national economy. These are building materials, facing, ornamental and precious stones (topaz, garnets, emerald, tourmaline, etc.), metal ores (Be, Zr, Al) and non-metals (B), rare elements. They find application in the rubber and paper industries, as refractories and ceramic raw materials.

    The solid shell of the Earth - the earth's crust - makes up only 1.5% of the total volume of the globe. But, despite this, it is the earth’s crust, or rather its upper layer, that is of greatest interest to us, since it is a source of mineral raw materials.
    Minerals- these are relatively homogeneous natural bodies that have certain chemical composition and physical properties. The name “mineral” comes from the Latin word “minera”, which literally means ore, ore. The science that studies the composition, structure and properties of minerals, their origin and conditions of occurrence is called mineralogy.
    Minerals are formed as a result of physical and chemical processes occurring in the earth's crust. Like all the nature around us, they consist of chemical elements. Figuratively speaking, a mineral is a kind of building made of bricks - chemical elements, built according to certain laws of nature. And just as man has built many different buildings on Earth from approximately the same number of bricks, nature has created more than 3 thousand different minerals in the earth’s crust from a relatively small number of chemical elements.

    In total, taking into account the numerous varieties, there are more than 7 thousand of their names, which are given to each mineral according to some characteristic.
    In the earth's crust, minerals are often found not independently, but as part of rocks. They largely determine the physical and mechanical properties of rocks and from this point of view are of the greatest interest for stone processing technology.
    Most minerals occur in nature in a solid state. Solid minerals can be crystalline or amorphous, differing in external geometric shape - regular for crystalline ones and indeterminate for amorphous ones.

    The shape of minerals depends on the arrangement of atoms in them. In crystalline minerals, atoms are arranged in a strictly defined order, forming a spatial lattice, due to which many minerals (for example, a quartz crystal) have the appearance of regular polyhedra. Crystalline minerals are anisotropic, that is, their physical properties are different in different directions. In amorphous minerals (usually in the form of beads), the atoms are arranged randomly. Such minerals are isotropic, that is, their physical properties are the same in all directions.

    Classification of minerals
    In accordance with the currently generally accepted chemical classification, all minerals can be divided into nine classes:
    I. Silicates are salts of silicic acids, among which there are subgroups of minerals that have some common composition and structure: feldspars, divided according to their chemical composition into plagioclases and orthoclases, pyroxenes, amphiboles, micas, olivine, talc, chlorites and clay minerals. This is the most numerous class, numbering up to 800 minerals.
    II. Carbonates are salts of carbonic acid, including up to 80 minerals, the most common of which are calcite, magnesite and dolomite.

    III. Oxides and hydroxides - combine about 200 minerals, among which the most common are quartz, opal, limonite, and hamatite.
    IV. Sulfides are compounds of elements with sulfur, numbering up to 200 minerals. A typical representative is pyrite.
    V. Sulfates - salts of sulfuric acid, including about 260 minerals,
    among which gypsum and anhydrite are the most widespread.
    VI. Halides are salts of halide acids, numbering about 100 min.
    Ralov. Typical representatives of halogens are halite (table salt) and
    fluorite

    Rocks. Structure and texture of rocks.

    Rocks. Structures and textures of rocks.

    Rocks. Structures and textures of rocks. - section Geology, Subject and methods of geology. The principle of actualism: uniformitarianism and the actualistic approach. Subject and methods of geology. Specifics of geology. Sections of modern geology. Specifics of Geology: Structure – Methods of Arrangement in Space of Grains of the World...

    Structure– ways of arranging grains of minerals in a rock in space. Characteristics of the volumetric structure of GP, determined by the shape, size and method of joining mineral individuals. Depends on the conditions of formation of the GP and is their main characteristic. They differ in the degree of crystallinity of the rock, the absolute and relative sizes of the crystals.

    Texture- mutual arrangement of mineral grains and their aggregates in space, general appearance of the rock (figure)

    Structure of igneous rocks:

    1) Full-crystalline - all parts of the rock are presented in the form of crystals

    2) The incompletely crystalline part of the rock solidified in the form of volcanic glass, the other

    3) Glassy rocks are represented by volcanic glass

    4) Cryptocrystalline (aphanitic) – grain size less than 0.1 mm

    5) Fine-crystalline (fine-grained) – crystal size. 0.1-1 mm

    6) Medium-crystalline - 1-5 mm

    7) Coarse crystalline – 5-10 mm

    8) Coarse or gigantocrystalline - more than 1 cm

    9) Uniformly crystalline, uniformly grained, unevenly grained

    10) Porphyritic - uneven-grained structures in which crystals of individual minerals stand out in large sizes against the background of glassy or cryptocrystalline groundmass

    11) Porphyritic - large crystals are immersed in the groundmass with clearly visible smaller grains

    12) Pegmatite - germination of KPSh with quartz

    Texture of igneous rocks:

    1) Dense (compact) - grains fit tightly to each other (volcanic glasses)

    2) Porous - the presence of cavities, pores

    3) Bubbly, foamy (slag, pumice)

    4) Almond stone - if the voids in the porous rock are filled with a secondary mineral (opal, chalcedony, etc.)

    5) Massive – homogeneous

    6) Banded - alternating stripes of different colors or different mineral compositions

    7) Fluid - traces of jets of flow of magmatic material

    8) Spotted - spotty, uneven distribution of colored minerals.

    Structure of metamorphic GPs:

    1) Microcrystalline - not distinguishable with the naked eye 2) Catoclastic (Clastic) - angular fragments of different sizes (breccia structure) 3) Full-crystalline (microcrystalline - 0.01-0.1 mm, fine-crystalline 0.1-1 mm, medium-crystalline 1-5 mm , coarse crystalline 5-10mm, gigantocrystalline >10mm)

    Texture of metamorphic GPs:

    1) Banded 2) Massive 3) Spectacled (rounded aggregates in a schistose mass) 4) Flat (small folds) 5) Schistose (rock is divided into plates) 6) Mottled

    Igneous rocks

    Origin and classification. Igneous (or igneous) rocks are rocks that were formed as a result of the crystallization of magma as it cooled in the bowels of the Earth or on its surface. Magma (or lava) is a complex silicate melt of approximately the following composition: oxygen - 46.7%, silicon - 27.7%, aluminum - 8.1%, iron - 5.1%, calcium - 3.6%, magnesium - 2.1%, sodium - 2.7%, potassium - 2.6%, other elements usually do not exceed an average of 1.4%. The temperature of the magma varies, but is usually 100 - 1300 °C.

    The history of the formation of igneous rocks begins with the formation of magma, which then successively changed under the influence of poorly studied complex interrelated physical, chemical, physicochemical processes. These processes are largely completed when the magma cools or crystallizes with the formation of aggregates of silicate minerals. Depending on the conditions under which cooling and solidification (loss of mobility) of magma occurs, rocks are divided into intrusive(deep) and effusive(outpoured) (Fig. 16).

    Effusive rocks are formed from the same magma as deep-seated rocks, which is why they are called analogues of deep-seated rocks. The varieties of these breeds will accordingly be vein And volcanic. When volcanic rocks form on the surface of the earth, magma is called lava.

    Some geologists believe that the origin of magma is based on a single primary magma of basaltic composition, and its further differentiation led to the formation of igneous rocks of different compositions.

    Sedimentary rocks.

    The content of the article

    MINERALS AND MINERALOGY.Minerals – solid natural formations that make up the rocks of the Earth, the Moon and some other planets, as well as meteorites and asteroids. Minerals, as a rule, are fairly homogeneous crystalline substances with an ordered internal structure and a certain composition, which can be expressed by an appropriate chemical formula. Minerals are not a mixture of tiny mineral particles, such as emery (consisting mainly of corundum and magnetite) or limonite (an aggregate of goethite and other iron hydroxides), but also compounds of elements with a disordered structure, like volcanic glasses (obsidian, etc.) .). Minerals are considered chemical elements or their compounds formed as a result of natural processes. The most important types of mineral raw materials of organic origin, such as coal and oil, are excluded from the list of minerals.

    Mineralogy– the science of minerals, their classification, chemical composition, features and patterns of structure (structure), origin, conditions in nature and practical application. For a deeper explanation of the internal structure of minerals and their connection with the history of the Earth, mineralogy involves mathematics, physics and chemistry. It uses quantitative data to a greater extent than other geological sciences, since fine chemical analysis and precise physical measurements are necessary to adequately describe minerals.

    HISTORY OF MINERALOGY

    Flint flakes with sharp edges were used primitive man as tools of labor already in the Paleolithic. Flint (a fine-grained variety of quartz) has long been a major mineral. In ancient times, other minerals were also known to man. Some of them, such as cherry hematite, yellow-brown goethite and black oxides of manganese, were used as paints for rock painting and body painting, while others, such as amber, jade, native gold, were used for making ritual objects, jewelry and amulets. In Egypt of the predynastic period (5000–3000 BC) many minerals were already known. Native copper, gold and silver were used for decoration. Somewhat later, tools and weapons began to be made from copper and its alloy, bronze. Many minerals were used as dyes, others for jewelry and signets (turquoise, jade, crystal, chalcedony, malachite, garnet, lapis lazuli and hematite). Currently, minerals serve as a source of metals, building materials (cement, plaster, glass, etc.), raw materials for the chemical industry, etc.

    In the first known treatise on mineralogy About stones Aristotle's student the Greek Theophrastus (c. 372–287 BC) minerals were divided into metals, earths and stones. About 400 years later, Pliny the Elder (23–79 AD) in five latest books Natural history summarized all the information on mineralogy available at that time.

    In the early Middle Ages in the countries of the Arab East, which adopted the knowledge of ancient Greece and ancient india, science flourished. The Central Asian scientist-encyclopedist Biruni (973 - ca. 1050) compiled descriptions of precious stones ( Mineralogy) and invented a method for accurately measuring their specific gravities. Another prominent scientist Ibn Sina (Avicenna) (c. 980–1037) in a treatise About stones gave a classification of all known minerals, dividing them into four classes: stones and earths, fossil fuels, salts, metals.

    In the Middle Ages in Europe, practical information about minerals was accumulated. The miner and prospector, out of necessity, became practicing mineralogists and passed on their experience and knowledge to students and apprentices. The first set of factual information on practical mineralogy, mining and metallurgy was the work of G. Agricola About metals (De re metallica), published in 1556. Thanks to this treatise and an earlier work About the nature of fossils (De natura fossilium, 1546), which contains a classification of minerals based on their physical properties, Agricola is known as the father of mineralogy.

    For 300 years after the publication of Agricola's works, research in the field of mineralogy was devoted to the study of natural crystals. In 1669, the Danish naturalist N. Stenon, summarizing his observations of hundreds of quartz crystals, established the law of constancy of angles between crystal faces. A century later (1772) Romé de Lisle confirmed Stenon's conclusions. In 1784, Abbot R. Gayuy laid the foundations for modern ideas about crystal structure. In 1809, W. Wollaston invented a reflective goniometer, which made it possible to carry out more precise measurements angles between crystal faces, and in 1812 he put forward the concept of a spatial lattice as a law of the internal structure of crystals. In 1815, P. Cordier proposed studying the optical properties of fragments of crushed minerals under a microscope. The further development of microscopic research is associated with the invention in 1828 by W. Nicol of a device for producing polarized light (Nicol prism). The polarizing microscope was improved in 1849 by G. Sorby, who applied it to the study of transparent thin sections of rocks.

    There was a need to classify minerals. In 1735 C. Linnaeus published a work System of nature (Systema naturae), in which minerals were classified according to external characteristics, i.e. just like plants and animals. Then Swedish scientists - A. Kronstedt in 1757 and J. Berzelius in 1815 and 1824 - proposed several options for chemical classifications of minerals. The second Berzelius classification, modified by K. Rammelsberg in 1841–1847, was firmly established after the American mineralogist J. Dana used it as the basis for the third edition Mineralogy systems (Dana's System of Mineralogy, 1850). Great contribution to the development of mineralogy in the 18th – first half of the 19th centuries. contributed by German scientists A.G. Werner and I.A. Breithaupt and Russians - M.V. Lomonosov and V.M. Severgin.

    In the second half of the 19th century. Improved polarizing microscopes, optical goniometers, and analytical techniques have made it possible to obtain more accurate data on individual mineral species. When crystals began to be studied using X-ray analysis, a deeper understanding of the structure of minerals came. In 1912, the German physicist M. Laue experimentally established that information about the internal structure of crystals can be obtained by passing X-rays through them. This method revolutionized mineralogy: the predominantly descriptive science became more accurate and mineralogists were able to link physical and Chemical properties minerals with their crystal structures.

    At the end of the 19th - beginning of the 20th century. The development of mineralogy was greatly facilitated by the work of outstanding Russian scientists N.I. Koksharov, V.I. Vernadsky, E.S. Fedorov, A.E. Fersman, A.K. Boldyrev and others. In the second half of the 20th century. mineralogy has adopted new research methods of solid state physics, in particular, infrared spectroscopy, a whole series of resonance methods (electron paramagnetic resonance, nuclear gamma resonance, etc.), luminescence spectroscopy, etc., as well as the latest analytical methods, including electron microprobe analysis, electron microscopy combined with electron diffraction, etc. The use of these methods makes it possible to determine the chemical composition of minerals “at a point”, i.e. on individual grains of minerals, study the subtle features of their crystal structure, the content and distribution of impurity elements, the nature of color and luminescence. The introduction of precise physical research methods produced a genuine revolution in mineralogy. The names of such Russian scientists as N.V. Belov, D.S. Korzhinsky, D.P. Grigoriev, I.I. Shafranovsky and others are associated with this stage in the development of mineralogy.

    MAIN PROPERTIES OF MINERALS

    For a long time, the main characteristics of minerals were the external shape of their crystals and other secretions, as well as physical properties (color, shine, cleavage, hardness, density, etc.), which are still of great importance in their description and visual (in particular, field ) diagnostics. These characteristics, as well as optical, chemical, electrical, magnetic and other properties, depend on the chemical composition and internal structure (crystalline structure) of minerals. The primary role of chemistry in mineralogy was recognized by the mid-19th century, but the importance of structure became apparent only with the introduction of radiography. The first decoding of crystal structures was carried out already in 1913 by English physicists W. G. Bragg and W. L. Bragg.

    Minerals are chemical compounds (with the exception of native elements). However, even colorless, optically transparent samples of these minerals almost always contain small amounts of impurities. Natural solutions or melts from which minerals crystallize usually consist of many elements. During the formation of compounds, a few atoms of less common elements can replace atoms of the main elements. Such substitution is so common that the chemical composition of many minerals only very rarely approaches that of the pure compound. For example, the composition of the common rock-forming mineral olivine varies within the compositions of two so-called. the final members of the series: from forsterite, magnesium silicate Mg 2 SiO 4, to fayalite, iron silicate Fe 2 SiO 4. The ratio of Mg:Si:O in the first mineral and Fe:Si:O in the second is 2:1:4. In olivines of intermediate composition, the ratios are the same, i.e. (Mg + Fe):Si:O is equal to 2:1:4, and the formula is written as (Mg,Fe) 2 SiO 4. If the relative amounts of magnesium and iron are known, then this can be reflected in the formula (Mg 0.80 Fe 0.20) 2 SiO 4, from which it can be seen that 80% of the metal atoms are represented by magnesium, and 20% by iron.

    Structure.

    All minerals, with the exception of water (which - unlike ice - is usually not classified as minerals) and, are represented as solids at ordinary temperatures. However, if water and mercury are greatly cooled, they solidify: water at 0° C, and mercury at -39° C. At these temperatures, water molecules and mercury atoms form a characteristic regular three-dimensional crystalline structure (the terms “crystalline” and “solid”) " in this case are almost equivalent). Thus, minerals are crystalline substances whose properties are determined by the geometric arrangement of their constituent atoms and the type of chemical bond between them.

    The unit cell (the smallest subdivision of a crystal) is made up of regularly arranged atoms held together by electronic bonds. These tiny cells, endlessly repeating in three-dimensional space, form a crystal. The sizes of unit cells in different minerals are different and depend on the size, number and relative arrangement of atoms within the cell. Cell parameters are expressed in angstroms (Å) or nanometers (1 Å = 10 –8 cm = 0.1 nm). The elementary cells of a crystal put together tightly, without gaps, fill the volume and form a crystal lattice. Crystals are divided based on the symmetry of the unit cell, which is characterized by the relationship between its edges and corners. Usually there are 7 systems (in order of increasing symmetry): triclinic, monoclinic, rhombic, tetragonal, trigonal, hexagonal and cubic (isometric). Sometimes trigonal and hexagonal systems are not separated and are described together under the name hexagonal system. Syngonies are divided into 32 crystal classes (types of symmetry), including 230 space groups. These groups were first identified in 1890 by the Russian scientist E.S. Fedorov. Using X-ray diffraction analysis, the dimensions of the unit cell of a mineral, its syngony, symmetry class and space group are determined, and the crystal structure is deciphered, i.e. the relative position in three-dimensional space of the atoms that make up the unit cell.

    GEOMETRIC (MORPHOLOGICAL) CRYSTALLOGRAPHY

    Crystals with their flat, smooth, shiny edges have long attracted human attention. Since the advent of mineralogy as a science, crystallography has become the basis for the study of the morphology and structure of minerals. It was found that the crystal faces have a symmetrical arrangement, which allows the crystal to be assigned to a certain system, and sometimes to one of the classes (symmetry) ( see above). X-ray studies have shown that the external symmetry of crystals corresponds to the internal regular arrangement of atoms.

    The sizes of mineral crystals vary over a very wide range - from giants weighing 5 tons (the mass of a well-formed quartz crystal from Brazil) to so small that their faces can only be distinguished under an electron microscope. The crystal shape of even the same mineral may differ slightly in different samples; for example, quartz crystals are almost isometric, acicular or flattened. However, all quartz crystals, large and small, pointed and flat, are formed by the repetition of identical unit cells. If these cells are oriented in a certain direction, the crystal has an elongated shape; if in two directions to the detriment of the third, then the shape of the crystal is tabular. Since the angles between the corresponding faces of the same crystal have a constant value and are specific to each mineral type, this feature is necessarily included in the characteristics of the mineral.

    Minerals represented by individual well-cut crystals are rare. Much more often they occur in the form of irregular grains or crystalline aggregates. Often a mineral is characterized by a certain type of aggregate, which can serve as a diagnostic feature. There are several types of units.

    Dendritic branching aggregates resemble fern leaves or moss and are characteristic, for example, of pyrolusite.

    Fibrous aggregates consisting of densely packed parallel fibers are typical of chrysotile and amphibole asbestos.

    Collomorphic aggregates, which have a smooth, rounded surface, are constructed from fibers that extend radially from a common center. Large round masses are mastoid (malachite), while smaller ones are kidney-shaped (hematite) or grape-shaped (psilomelane).

    Scaly aggregates consisting of small plate-like crystals are characteristic of mica and barite.

    Stalactites are drip-drip formations hanging in the form of icicles, tubes, cones or “curtains” in karst caves. They arise as a result of the evaporation of mineralized water seeping through limestone cracks, and are often composed of calcite (calcium carbonate) or aragonite.

    Oolites, aggregates consisting of small balls and resembling fish eggs, are found in some calcite (oolitic limestone), goethite (oolitic iron ore) and other similar formations.

    CRYSTAL CHEMISTRY

    After accumulating x-ray data and comparing them with the results of chemical analyses, it became obvious that the features of the crystal structure of a mineral depend on its chemical composition. Thus, the foundations of a new science - crystal chemistry - were laid. Many seemingly unrelated properties of minerals can be explained by taking into account their crystal structure and chemical composition.

    Some chemical elements (gold, silver, copper) are found in native, i.e. pure, form. They are built from electrically neutral atoms (unlike most minerals, whose atoms carry an electrical charge and are called ions). An atom with a lack of electrons is positively charged and is called a cation; an atom with an excess of electrons has a negative charge and is called an anion. The attraction between oppositely charged ions is called ionic bonding and serves as the main binding force in minerals.

    With another type of bond, outer electrons rotate around the nuclei in common orbits, connecting the atoms to each other. A covalent bond is the strongest type of bond. Minerals with covalent bonds usually have high hardness and melting points (for example, diamond).

    A much smaller role in minerals is played by the weak van der Waals bond that occurs between electrically neutral structural units. The binding energy of such structural units (layers or groups of atoms) is distributed unevenly. Van der Waals bonds provide attraction between oppositely charged regions in larger structural units. This type of bond is observed between layers of graphite (one of the natural forms of carbon), formed due to strong covalent bond carbon atoms. Due to the weak bonds between the layers, graphite has low hardness and very perfect cleavage, parallel to the layers. Therefore, graphite is used as a lubricant.

    Oppositely charged ions approach each other to a distance at which the repulsive force balances the attractive force. For any particular cation-anion pair, this critical distance is equal to the sum of the “radii” of the two ions. By determining the critical distances between different ions, it was possible to determine the size of the radii of most ions (in nanometers, nm).

    Since most minerals are characterized by ionic bonds, their structures can be visualized in the form of touching balls. The structures of ionic crystals depend mainly on the magnitude and sign of the charge and the relative sizes of the ions. Since the crystal as a whole is electrically neutral, the sum of the positive charges of the ions must be equal to the sum of the negative ones. In sodium chloride (NaCl, the mineral halite), each sodium ion has a charge of +1, and each chloride ion -1 (Fig. 1), i.e. Each sodium ion corresponds to one chloride ion. However, in fluorite (calcium fluoride, CaF 2), each calcium ion has a charge of +2, and the fluoride ion –1. Therefore, to maintain the overall electrical neutrality of fluorine ions, it must be twice as much as calcium ions (Fig. 2).

    The possibility of their inclusion in a given crystal structure also depends on the size of the ions. If the ions are the same size and are packed in such a way that each ion touches 12 others, then they are in appropriate coordination. There are two ways to pack balls of the same size (Fig. 3): cubic dense packing, in general case leading to the formation of isometric crystals, and hexagonal close packing, forming hexagonal crystals.

    As a rule, cations are smaller in size than anions, and their sizes are expressed in fractions of the anion radius, taken as one. Typically the ratio obtained by dividing the radius of the cation by the radius of the anion is used. If a cation is only slightly smaller than the anions with which it combines, it can be in contact with the eight anions surrounding it, or, as is commonly said, in eight-fold coordination with respect to the anions, which are located, as it were, at the vertices of a cube around it. This coordination (also called cubic) is stable at ionic radius ratios from 1 to 0.732 (Fig. 4, A). At a smaller ionic radius ratio, eight anions cannot be stacked to touch the cation. In such cases, the packing geometry allows for sixfold coordination of cations with anions located at six vertices of the octahedron (Fig. 4, b), which will be stable at ratios of their radii from 0.732 to 0.416. With a further decrease in the relative size of the cation, a transition occurs to quaternary, or tetrahedral, coordination, which is stable at radius ratios from 0.414 to 0.225 (Fig. 4, V), then to triple – within radius ratios from 0.225 to 0.155 (Fig. 4, G) and double – with radius ratios less than 0.155 (Fig. 4, d). Although other factors also determine the type of coordination polyhedron, for most minerals the ionic radius ratio principle is one effective means of predicting crystal structure.

    Minerals of completely different chemical compositions can have similar structures that can be described using the same coordination polyhedra. For example, in sodium chloride NaCl, the ratio of the radius of the sodium ion to the radius of the chlorine ion is 0.535, indicating octahedral, or six-fold, coordination. If six anions cluster around each cation, then to maintain a 1:1 cation to anion ratio, there must be six cations around each anion. This produces a cubic structure known as the sodium chloride type structure. Although the ionic radii of lead and sulfur differ sharply from the ionic radii of sodium and chlorine, their ratio also determines the sixfold coordination, therefore PbS galena has a structure like sodium chloride, i.e. halite and galena are isostructural.

    Impurities in minerals are usually present in the form of ions that replace those of the host mineral. Such substitutions greatly affect the sizes of ions. If the radii of two ions are equal or differ by less than 15%, they are easily substituted. If this difference is 15–30%, such substitution is limited; with a difference of more than 30%, substitution is practically impossible.

    There are many examples of pairs of isostructural minerals with similar chemical compositions between which ion substitution occurs. Thus, the carbonates siderite (FeCO 3) and rhodochrosite (MnCO 3) have similar structures, and iron and manganese can replace each other in any ratio, forming the so-called. solid solutions. There is a continuous series of solid solutions between these two minerals. In other pairs of minerals, ions have limited possibilities for mutual substitution.

    Since minerals are electrically neutral, the charge of the ions also affects their mutual substitution. If substitution occurs with an oppositely charged ion, then a second substitution must take place in some part of this structure, in which the charge of the substituting ion compensates for the violation of electrical neutrality caused by the first. Such conjugate substitution is observed in feldspars - plagioclases, when calcium (Ca 2+) replaces sodium (Na +) with the formation of a continuous series of solid solutions. The excess positive charge resulting from the replacement of the Na + ion by the Ca 2+ ion is compensated by the simultaneous replacement of silicon (Si 4+) with aluminum (Al 3+) in adjacent areas of the structure.

    PHYSICAL PROPERTIES OF MINERALS

    Although the main characteristics of minerals (chemical composition and internal crystal structure) are established on the basis of chemical analyzes and X-ray diffraction, they are indirectly reflected in properties that are easily observed or measured. To diagnose most minerals, it is enough to determine their luster, color, cleavage, hardness, and density.

    Shine

    – qualitative characteristic of light reflected by a mineral. Some opaque minerals reflect light strongly and have a metallic luster. This is common in ore minerals such as galena (lead mineral), chalcopyrite and bornite (copper minerals), argentite and acanthite (silver minerals). Most minerals absorb or transmit a significant portion of the light falling on them and have a non-metallic luster. Some minerals have a luster that transitions from metallic to non-metallic, which is called semi-metallic.

    Minerals with a non-metallic luster are usually light-colored, some of them are transparent. Quartz, gypsum and light mica are often transparent. Other minerals (for example, milky white quartz) that transmit light, but through which objects cannot be clearly distinguished, are called translucent. Minerals containing metals differ from others in light transmission. If light passes through a mineral, at least in the thinnest edges of the grains, then it is, as a rule, non-metallic; if the light does not pass through, then it is ore. There are, however, exceptions: for example, light-colored sphalerite (zinc mineral) or cinnabar (mercury mineral) are often transparent or translucent.

    Minerals differ in the qualitative characteristics of their non-metallic luster. The clay has a dull, earthy sheen. Quartz on the edges of crystals or on fracture surfaces is glassy, ​​talc, which is divided into thin leaves along the cleavage planes, is mother-of-pearl. Bright, sparkling, like a diamond, shine is called diamond.

    When light falls on a mineral with a non-metallic luster, it is partially reflected from the surface of the mineral and partially refracted at this boundary. Each substance is characterized by a certain refractive index. Because it can be measured with high precision, it is a very useful mineral diagnostic feature.

    The nature of the luster depends on the refractive index, and both of them depend on the chemical composition and crystal structure of the mineral. In general, transparent minerals containing heavy metal atoms are characterized by high luster and a high refractive index. This group includes such common minerals as anglesite (lead sulfate), cassiterite (tin oxide) and titanite or sphene (calcium titanium silicate). Minerals composed of relatively light elements can also have high luster and a high refractive index if their atoms are tightly packed and held together by strong chemical bonds. A notable example is diamond, which is composed of only one light element, carbon. To a lesser extent, this is true for the mineral corundum (Al 2 O 3), the transparent colored varieties of which - ruby ​​and sapphires - are precious stones. Although corundum is composed of light atoms of aluminum and oxygen, they are so tightly bound together that the mineral has a fairly strong luster and a relatively high refractive index.

    Some glosses (oily, waxy, matte, silky, etc.) depend on the state of the surface of the mineral or on the structure of the mineral aggregate; a resinous luster is characteristic of many amorphous substances (including minerals containing the radioactive elements uranium or thorium).

    Color

    – a simple and convenient diagnostic sign. Examples include brass-yellow pyrite (FeS 2), lead-gray galena (PbS) and silver-white arsenopyrite (FeAsS 2). In other ore minerals with a metallic or semi-metallic luster, the characteristic color may be masked by the play of light in a thin surface film (tarnish). This is common to most copper minerals, especially bornite, which is called "peacock ore" because of its iridescent blue-green tarnish that quickly develops when freshly fractured. However, other copper minerals are painted in familiar colors: malachite is green, azurite is blue.

    Some non-metallic minerals are unmistakably recognizable by the color determined by the main chemical element (yellow - sulfur and black - dark gray - graphite, etc.). Many non-metallic minerals consist of elements that do not provide them with a specific color, but they have colored varieties, the color of which is due to the presence of impurities of chemical elements in small quantities that are not comparable with the intensity of the color they cause. Such elements are called chromophores; their ions are characterized by selective absorption of light. For example, the deep purple amethyst owes its color to a trace amount of iron in quartz, while the deep green color of emerald is due to the small amount of chromium in beryl. Colors in normally colorless minerals can result from defects in the crystal structure (caused by unfilled atomic positions in the lattice or the incorporation of foreign ions), which can cause selective absorption of certain wavelengths in the white light spectrum. Then the minerals are painted in additional colors. Rubies, sapphires and alexandrites owe their color to precisely these light effects.

    Colorless minerals can be colored by mechanical inclusions. Thus, thin scattered dissemination of hematite gives quartz a red color, chlorite - green. Milky quartz is clouded with gas-liquid inclusions. Although mineral color is one of the most easily determined properties in mineral diagnostics, it must be used with caution as it depends on many factors.

    Despite the variability in the color of many minerals, the color of the mineral powder is very constant, and therefore is an important diagnostic feature. Typically, the color of a mineral powder is determined by the line (the so-called “line color”) that the mineral leaves when it is passed over an unglazed porcelain plate (biscuit). For example, the mineral fluorite is colored different colors, but his line is always white.

    Cleavage.

    A characteristic property of minerals is their behavior when splitting. For example, quartz and tourmaline, whose fracture surface resembles a glass chip, have a conchoidal fracture. In other minerals, the fracture may be described as rough, jagged, or splintered. For many minerals, the characteristic is not fracture, but cleavage. This means that they cleave along smooth planes directly related to their crystal structure. Coupling forces between planes crystal lattice may vary depending on the crystallographic direction. If they are much larger in some directions than in others, then the mineral will split across the weakest bond. Since cleavage is always parallel to the atomic planes, it can be designated by indicating crystallographic directions. For example, halite (NaCl) has cube cleavage, i.e. three mutually perpendicular directions of possible split. Cleavage is also characterized by the ease of manifestation and the quality of the resulting cleavage surface. Mica has very perfect cleavage in one direction, i.e. easily splits into very thin leaves with a smooth shiny surface. Topaz has perfect cleavage in one direction. Minerals can have two, three, four or six cleavage directions along which they are equally easy to split, or several cleavage directions of varying degrees. Some minerals have no cleavage at all. Since cleavage, as a manifestation of the internal structure of minerals, is their constant property, it serves as an important diagnostic feature.

    Hardness

    – the resistance that a mineral provides when scratched. Hardness depends on the crystal structure: the more tightly the atoms in the structure of a mineral are connected to each other, the more difficult it is to scratch it. Talc and graphite are soft plate-like minerals, built from layers of atoms bonded together by very weak forces. They are greasy to the touch: when rubbed against the skin of the hand, individual thin layers slip off. The hardest mineral is diamond, in which the carbon atoms are so tightly bonded that it can only be scratched by another diamond. At the beginning of the 19th century. Austrian mineralogist F. Moos arranged 10 minerals in increasing order of their hardness. Since then, they have been used as standards for the relative hardness of minerals, the so-called. Mohs scale (Table 1).

    To determine the hardness of a mineral, it is necessary to identify the hardest mineral that it can scratch. The hardness of the mineral being examined will be greater than the hardness of the mineral it scratched, but less than the hardness of the next mineral on the Mohs scale. Bonding forces can vary depending on the crystallographic direction, and since hardness is a rough estimate of these forces, it can vary in different directions. This difference is usually small, with the exception of kyanite, which has a hardness of 5 in the direction parallel to the length of the crystal and 7 in the transverse direction.

    In mineralogical practice, the measurement of absolute hardness values ​​(so-called microhardness) using a sclerometer device, which is expressed in kg/mm ​​2, is also used.

    Density.

    The mass of atoms of chemical elements varies from hydrogen (the lightest) to uranium (the heaviest). All other things being equal, the mass of a substance consisting of heavy atoms is greater than that of a substance consisting of light atoms. For example, two carbonates - aragonite and cerussite - have a similar internal structure, but aragonite contains light calcium atoms, and cerussite contains heavy lead atoms. As a result, the mass of cerussite exceeds the mass of aragonite of the same volume. The mass per unit volume of a mineral also depends on the atomic packing density. Calcite, like aragonite, is calcium carbonate, but in calcite the atoms are less densely packed, so it has less mass per unit volume than aragonite. The relative mass, or density, depends on the chemical composition and internal structure. Density is the ratio of the mass of a substance to the mass of the same volume of water at 4° C. So, if the mass of a mineral is 4 g, and the mass of the same volume of water is 1 g, then the density of the mineral is 4. In mineralogy, it is customary to express density in g/ cm 3.

    Density is an important diagnostic feature of minerals and is not difficult to measure. First, the sample is weighed in air and then in water. Since a sample immersed in water is subject to an upward buoyant force, its weight there is less than in air. The weight loss is equal to the weight of water displaced. Thus, density is determined by the ratio of the mass of a sample in air to its weight loss in water.

    CLASSIFICATION OF MINERALS

    Although chemical composition has served as the basis for the classification of minerals since the mid-19th century, mineralogists have not always shared a common opinion on what the order of minerals should be in it. According to one method of constructing a classification, minerals were grouped according to the same main metal or cation. In this case, iron minerals fell into one group, lead minerals into another, zinc minerals into a third, etc. However, as science developed, it turned out that minerals containing the same non-metal (anion or anionic group) have similar properties and are much more similar to each other than minerals with a common metal. In addition, minerals with a common anion occur in the same geological setting and are of similar origin. As a result, in modern taxonomy ( cm. table 2) minerals are grouped into classes based on their common anion or anionic group. The only exception is native elements, which occur in nature by themselves, without forming compounds with other elements.

    Table 2. Classification of minerals
    Table 2. CLASSIFICATION OF MINERALS
    Class Mineral (example) Chemical formula
    Native elements Gold Au
    Carbides 1 Moissanite SiC
    Sulfides 2 and sulfosalts Cinnabar
    Enargite    		 HgS
    Cu 3 AsS 4
    Oxides Hematite Fe2O3
    Hydroxides Brucite Mg(OH)2
    Halides Fluorite CaF2
    Carbonates Calcite CaCO3
    Nitrates Potassium nitrate KNO 3
    Borats Borax Na 2 B 4 O 5 (OH)4Х8H 2 O
    Phosphates 3 Apatite Ca5(PO4)3F
    Sulfates Gypsum CaSO 4H 2H 2 O
    Chromates Crocoite PbCrO4
    Tungstates 4 Sheelit CaWO 4
    Silicates Albite NaAlSi3O8
    Including nitrides and phosphides
    2 Including arsenides, selenides and tellurides.
    3 Including arsenates and vanadates.
    4 Including molybdates.

    Chemical classes are divided into subclasses (based on chemistry and structural motif), which, in turn, are divided into families and groups (based on structural type). Individual mineral species within a group may form rows, and one mineral species may have several varieties.

    By now approx. 4000 minerals are recognized as independent mineral species. New minerals are added to this list as they are discovered and long-known, but discredited, as methods of mineralogical research are improved, they are excluded.

    ORIGIN AND CONDITIONS OF FINDING MINERALS

    Mineralogy is not limited to determining the properties of minerals; it also studies the origin, conditions of occurrence and natural associations of minerals. Since the origin of the Earth approximately 4.6 billion years ago, many minerals have been destroyed by mechanical crushing, chemical transformation or melting. But the elements that made up these minerals were preserved, regrouped and formed new minerals. Thus, the minerals that exist today are the products of processes that developed throughout the geological history of the Earth.

    Most of the earth's crust is composed of igneous rocks, which in some places are covered by a relatively thin cover of sedimentary and metamorphic rocks. Therefore, the composition of the earth's crust, in principle, corresponds to the average composition of the igneous rock. Eight elements ( see table 3) make up 99% of the mass of the earth's crust and, accordingly, 99% of the mass of the minerals composing it.

    Element Mass percent Volume percent Oxygen 46.40 94.04 Silicon 28.15 0.88 Aluminum 8.23 ​​0.48 Iron 5.63 0.49 Calcium 4.15 1.18 Sodium 2.36 1.11 Magnesium 2, 33 0.33 Potassium 2.09 1.49

    In terms of elemental composition, the earth's crust is a frame structure consisting of oxygen ions associated with smaller ions of silicon and aluminum. Thus, the main minerals are silicates, which account for approx. 35% of all known minerals and approx. 40% – the most common. The most important of them are feldspars (a family of aluminosilicates containing potassium, sodium and calcium, and less often barium). Other common rock-forming silicates are quartz (however, it is more often classified as oxides), micas, amphiboles, pyroxenes and olivine.

    Igneous rocks.

    Igneous, or igneous, rocks are formed when molten magma cools and crystallizes. The percentages of different minerals, and therefore the type of rock formed, depend on the ratio of elements contained in the magma at the time it solidified. Each type of igneous rock usually consists of a limited set of minerals called major rocks. In addition to them, minor and accessory minerals may be present in smaller quantities. For example, the main minerals in granite may be potassium feldspar (30%), sodium calcium feldspar (30%), quartz (30%), micas and hornblende (10%). Zircon, sphene, apatite, magnetite and ilmenite may be present as accessory minerals.

    Igneous rocks are usually classified based on the type and amount of each feldspar they contain. However, some rocks lack feldspar. Igneous rocks are further classified by their structure, which reflects the conditions under which the rock solidified. Slowly crystallizing deep within the Earth, magma gives rise to intrusive plutonic rocks with a coarse- to medium-grained structure. If magma erupts to the surface as lava, it quickly cools and produces fine-grained volcanic (effusive, or extrusive) rocks. Sometimes some volcanic rocks (for example, obsidian) cool so quickly that they do not have time to crystallize; similar rocks have a glassy appearance (volcanic glasses).

    Sedimentary rocks.

    When bedrock is weathered or eroded, clastic or dissolved material becomes incorporated into the sediment. As a result of chemical weathering of minerals, which occurs at the boundary of the lithosphere and atmosphere, new minerals are formed, for example, clay minerals from feldspar. Some elements are released when minerals (such as calcite) dissolve in surface waters. However, other minerals, such as quartz, even mechanically crushed, remain resistant to chemical weathering.

    Mechanically and chemically stable minerals with a sufficiently high density released during weathering form placer deposits on the earth's surface. From placers, most often alluvial (river), gold, platinum, diamonds, other precious stones, tin stone (cassiterite), and minerals of other metals are mined. Under certain climatic conditions, thick weathering crusts are formed, often enriched with ore minerals. Weathering crusts are associated with industrial deposits of bauxite (aluminum ores), accumulations of hematite (iron ores), hydrous nickel silicates, niobium minerals and other rare metals.

    The bulk of weathering products is carried through a system of watercourses into lakes and seas, at the bottom of which it forms a layered sedimentary layer. Shales are composed primarily of clay minerals, while sandstone is composed primarily of cemented quartz grains. Dissolved material may be removed from the water by living organisms or precipitated through chemical reactions and evaporation. Calcium carbonate is absorbed from seawater by mollusks, which use it to build their hard shells. Most limestones are formed by the accumulation of shells and skeletons of marine organisms, although some calcium carbonate is precipitated chemically.

    Evaporite deposits are formed as a result of the evaporation of sea water. Evaporites are a large group of minerals, which include halite (table salt), gypsum and anhydrite (calcium sulfates), sylvite (potassium chloride); they all have important practical applications. These minerals are also deposited during evaporation from the surface of salt lakes, but in this case, an increase in the concentration of rare elements can lead to additional precipitation of some other minerals. It is in this environment that borates are formed.

    Metamorphic rocks.

    Regional metamorphism.

    Igneous and sedimentary rocks buried at great depths, under the influence of temperature and pressure, undergo transformations called metamorphic, during which the original properties of the rocks change, and the original minerals recrystallize or are completely transformed. As a result, minerals are usually arranged along parallel planes, giving the rocks a schistose appearance. Thin schistose metamorphic rocks are called shales. They are often enriched in plate silicate minerals (mica, chlorite or talc). Coarser schistose metamorphic rocks are gneisses; they contain alternating bands of quartz, feldspar and dark-colored minerals. When schists and gneisses contain some typically metamorphic mineral, this is reflected in the name of the rock, for example, sillimanite or staurolite schist, kyanite or garnet gneiss.

    Contact metamorphism.

    When magma rises to the upper layers of the earth's crust, changes usually occur in the rocks into which it has intruded, the so-called. contact metamorphism. These changes are manifested in the recrystallization of the original or the formation of new minerals. The extent of metamorphism depends on both the type of magma and the type of rock it pervades. Clayey rocks and rocks similar in chemical composition are transformed into contact hornfels (biotite, cordierite, garnet, etc.). The most intense changes occur when granitic magma intrudes into limestones: thermal effects cause their recrystallization and the formation of marble; As a result of chemical interaction with limestones, the solutions separated from the magma form a large group of minerals (calcium and magnesium silicates: wollastonite, grossular and andradite garnets, vesuvianite, or idocrase, epidote, tremolite and diopside). In some cases, contact metamorphism introduces ore minerals, making the rocks valuable sources of copper, lead, zinc and tungsten.

    Metasomatosis.

    As a result of regional and contact metamorphism, there is no significant change in the chemical composition of the original rocks, but only their mineral composition and appearance change. When solutions introduce some elements and remove others, a significant change in the chemical composition of the rocks occurs. Such newly formed rocks are called metosomatic. For example, the interaction of limestones with solutions released by granitic magma during crystallization leads to the formation around granite massifs of zones of contact-metasomatic ores - scarps, which often host mineralization.

    ORE DEPOSITS AND PEGMATITE

    The chemical composition of coarse-grained granite can differ significantly from the composition of the original magma. The study of rocks showed that minerals are released from magma in a certain sequence. Iron- and magnesium-rich minerals such as olivine and pyroxenes, as well as accessory minerals, crystallize first. Due to their higher density than the surrounding melt, they settle downward as a result of the process of magmatic segregation. It is believed that dunites are formed in this way - rocks consisting almost entirely of olivine. Similar origins are attributed to some large accumulations of magnetite, ilmenite and chromite, which are the iron, titanium and chromium series respectively.

    However, the composition of the melt remaining after minerals are removed by magmatic segregation is not completely identical to the composition of the rock formed from it. During the crystallization of the melt, the concentration of water and other volatile components (for example, fluorine and boron compounds) increases in it, and along with them many other elements whose atoms are too large or too small to enter the crystalline structures of rock-forming minerals. Aqueous fluids released from crystallizing magma can rise through cracks to the Earth's surface, into an area of ​​lower temperatures and pressures. This causes the deposition of minerals in cracks and the formation of vein deposits. Some veins are composed mainly of non-metallic minerals (quartz, calcite, barite and fluorite). Other veins contain minerals of metals such as gold, silver, copper, lead, zinc, tin and mercury; accordingly, they may represent valuable ore deposits. Since such deposits are formed with the participation of heated aqueous solutions, they are called hydrothermal. It should be said that the largest hydrothermal deposits are not vein, but metasomatic; they are sheet-like or other shaped deposits formed by replacing rocks (most often limestone) with ore-bearing solutions. The minerals that make up such deposits are said to be of hydrothermal-metasomatic origin.

    Pegmatites are genetically related to crystallizing granitic magma. A mass of highly mobile fluid, still rich in the elements that make up the rock-forming minerals, can be ejected from the magma chamber into the host rock, where it crystallizes to form bodies of a coarse-grained structure, composed mainly of rock-forming minerals - quartz, feldspar and mica. Such rock bodies, called pegmatites, are highly variable in size. The maximum length of most pegmatite bodies is several hundred meters, but the largest of them reach a length of 3 km, and for small ones it is measured in the first meters. Pegmatites contain large crystals of individual minerals, including the world's largest feldspar crystals several meters long, mica - up to 3 m in diameter, quartz - weighing up to 5 tons.

    Some pegmatite-forming fluids concentrate rare elements (often in the form of large crystals), for example, beryllium in beryl and chrysoberyl, lithium in spodumene, petalitite, amblygonite and lepidolite, cesium in hecite, boron in tourmaline, fluorine in apatite and topaz. Most of these minerals are of jewelry varieties. The industrial importance of pegmatites is partly due to the fact that they are a source of precious stones, but mainly - high-grade potassium feldspar and mica, as well as ores of lithium, cesium and tantalum, and partly beryllium.


    Literature:

    Minerals: Directory, vol. 1–4. M., 1960–1992
    Fleisher M. Dictionary of mineral species. M., 1980
    Mineralogical Encyclopedia. L., 1985
    Berry L., Mason B., Dietrich R. Mineralogy. M., 1987

    

    Classes of native elements and sulfides.

    The most common mineral of the first class is sulfur. S. It is used in the chemical industry to produce sulfuric acid, in agriculture and in a number of other industries.

    Graphite WITH associated primarily with metamorphic processes. Widely used in metallurgy, for the production of electrodes, etc. This class includes such valuable minerals as diamond, gold, platinum, etc.

    Numerous minerals - metal ores - belong to the sulfide class.

    Galena, or lead luster PbS, - occurs in the form of crystalline aggregates, less often - individual crystals and their intergrowths. Cubic system. Color: lead gray; streak greyish-black, shiny; metallic luster; opaque.

    Sphalerite, or zinc blende ZnS, - occurs in the form of crystalline aggregates, less often intergrowths of cubic crystals. The color is brown, rarely colorless, sometimes black with iron impurities; streak yellow, brown; diamond, metallic luster; shines through; cleavage is perfect.

    Class of halogen compounds.

    It includes minerals that are salts of fluoric, bromic, hydrochloric, and hydroiodic acids.

    The most common minerals of this class are chlorides, which are formed mainly by the evaporation of water from surface pools. Chlorides are also known to be released from volcanic gases.

    Halite NaCI- forms dense crystalline aggregates, less often cubic crystals. Pure halite is colorless or white, often painted in various light colors; hygroscopic, salty taste. Used in the food industry and chemical industry to produce chlorine, sodium and their derivatives.

    Silvin KCl- is close in origin and physical properties to halite, with which it often forms single aggregates. Distinctive feature- bitter-salty taste. It is mainly used as a raw material for potash fertilizers and in the chemical industry.

    Fluorides are associated primarily with hydrothermal, as well as with magmatic and pneumatolytic processes (Greek “pneuma” - spirit, gas). Rarely formed under exogenous conditions. These include fluorite, or fluorspar - CaF2, found in the form of granular clusters, individual crystals and their intergrowths.

    Class of oxides and hydroxides.

    It occupies one of the first places in terms of the number of minerals it contains: it accounts for about 17% of the total mass of the earth’s crust. Of these, about 12.5% ​​are silicon oxides and 3.9% are iron oxides. Minerals of this class are formed under both endogenous and exogenous conditions.

    Quartz SiO 2 is a widespread rock-forming mineral in the earth’s crust. Quartz occurs in the form of granular aggregates, dense masses, grains in rocks, and forms crystals and intergrowths in voids. The crystals have a complex shape, the basis of which is a hexagonal prism ending in rhombohedrons. The color is varied - colorless, white, gray, there are colored varieties. Color is the basis for distinguishing varieties of quartz: rock crystal - colorless transparent crystals; smoky quartz - gray-smoky, brown; amethyst - purple crystals; morion - black, etc.; translucent, less often transparent. Quartz is released during the crystallization of magma, falls out of hot solutions and vapors, and appears during the process of metamorphism. It is rarely formed under exogenous conditions. Chemically stable in all conditions.


    Chalcedony SiO 2 is a cryptocrystalline mineral that forms dense, often sintered masses. The color varies, often yellow-brown tones. Quartz and chalcedony are used in the glass, chemical industries, and construction; rock crystal (piezoquartz) is used in optics and radio engineering. Beautifully colored varieties are used in jewelry. The deposits are numerous.

    Opal SiO2.nH2O- amorphous mineral. It forms dense, often sintered masses, and composes some sedimentary rocks of organogenic origin. Colorless, white, gray, sometimes colored by impurities various colors. It is formed during the weathering of silicates, as a result of the vital activity of certain organisms; also precipitates from hot solutions, forming geyserites. It is used in jewelry as an ornamental stone and in construction as an abrasive material.

    Iron oxide minerals are widely distributed in nature. Hematite, or iron luster Fe 2 O 3, forms dense fine-crystalline aggregates of a scaly structure, cryptocrystalline masses (red iron ore), as well as nodules (nodules) of a radial or shell-like structure. The color ranges from yellow-gray, steel-gray and almost black in crystalline varieties to dark red in cryptocrystalline ones; the color of the line is from red-brown to cherry-red.

    Magnetite, or magnetic iron ore FeО.Fe 2 О 3, or FeFe 2 O 4, usually forms dense crystalline aggregates. Cubic system. Its properties resemble the crystalline variety of hematite, but differs from it in its black color and magnetic properties. The formation of hematite and magnetite is associated mainly with endogenous processes - magmatic, hydrothermal and metamorphic. Hematite can also occur under exogenous conditions (during weathering, in the marine environment).

    Limonite, or brown iron ore, is an aggregate of related minerals - goethite FeOOH, hydrogoethite FeOOH.nH 2 O, lepidocrocite FeO(OH) and clay particles, the ratios of which are not constant. Limonite forms dense sintered or earthy loose masses, nodules and oolites. It is often possible to observe transitions of dense differences into loose ones in one sample. The color of loose varieties is ocher-yellow, and that of dense varieties is black; the trait is yellow-brown or brown, respectively. The formation of limonite is associated with the weathering of iron-containing minerals, as well as precipitation from surface waters, and microorganisms play a major role in this process.

    A valuable mineral resource for aluminum is bauxite, which, like limonite, is an aggregate of minerals - aluminum oxides and hydroxides: diaspora AlOOН, hydrargillite Al(OH) 3, boehmite AlO(OH) with an admixture of iron oxides, silicon oxide, etc. They are found in the form of earthy, loose or solid masses, often forming oolitic accumulations. Color: white, gray, yellow, often red, brown-red. They are formed during the weathering of rocks that are rich in minerals containing aluminum, and during the subsequent redeposition of weathering products.

    Carbonate class combines a large number of minerals that are characterized by a reaction with hydrochloric acid accompanied by the release of carbon dioxide. The intensity of the reaction helps to distinguish between minerals - carbonates, which are similar in many properties. They are often light-colored, with a glassy sheen; hardness 3-4.5; cleavage perfect in three directions. The formation of carbonates is associated mainly with surface chemical and biochemical processes, as well as metamorphic and hydrothermal ones.

    Calcite, or lime spar Ca[CO 3 ],- one of the most common minerals in the earth’s crust, participating in the structure of both sedimentary and metamorphic rocks. It occurs in the form of crystalline and cryptocrystalline aggregates of varying densities, in voids in the form of various sinter forms, crystals and their intergrowths. The color is varied - from colorless and white, occasionally to black; (colorless transparent calcite crystals that are birefringent are called Iceland spar); reacts violently (“boils”) with hydrochloric acid. The application is varied: in construction, in the metallurgical and chemical industries, as an ornamental stone, Iceland spar - in optics.

    Dolomite CaMg[CO 3 ] 2- a common mineral that forms crystalline and earthy aggregates. It differs from calcite in slightly greater hardness and density, and most importantly, in its reaction with hydrochloric acid, which occurs only with dolomite powder. Used in metallurgy and construction.

    Minerals of the sulfate class are deposited in surface reservoirs, formed during the oxidation of sulfides and sulfur in weathering zones, and are less commonly associated with volcanic activity.

    Anhydrite Ca- forms dense fine-crystalline clusters. The color is white, often with a blue or gray tint; glass luster, pearlescent; transparent, often translucent; cleavage is perfect in one direction and average in two. Used for cement production and for crafts.

    The most common sulfate mineral is gypsum. Ca2H2O, found in the form of fine-crystalline and earthy aggregates, individual crystals and their intergrowths. Usually white, sometimes painted in light colors; glass luster, pearlescent, silky; transparent or translucent; The cleavage in one direction is very perfect, in the other it is average. Used in construction, chemical industry, medicine, etc.

    Phosphate class . The most common mineral is apatite Ca 5 [PO 4 ] 3 (F, OH, Cl)(the content of fluorine, chlorine and hydroxyl group varies). It occurs in the form of crystalline aggregates and individual crystals. The color is colorless, often pale green and greenish blue. The origin is igneous. Widely used in fertilizer and chemical industries.

    Silicate class . Minerals of this class are widespread in the earth's crust (over 78%). They are formed predominantly under endogenous conditions, being associated with various manifestations of magmatism and metamorphic processes. Only a few of them arise under exogenous conditions. Many minerals of this class are rock-forming igneous and metamorphic rocks, less often sedimentary rocks.

    Silicates are characterized by a complex chemical composition and internal structure. Minerals containing aluminum ions are called aluminosilicates.

    Internal structure silicates and aluminosilicates largely determines their properties: minerals with an island structure, characterized by dense packing of ions, often form isometric crystals, have high hardness, density and imperfect cleavage. Minerals with linearly elongated structures (chain and ribbon) form prismatic crystals with well-defined cleavage in two directions along the long axis of the structure. Minerals with a layered structure form tabular crystals with very perfect cleavage, parallel to the “layers” of the structure.

    Island silicates. Olivine, or peridot, ( Mg,Fe) 2 , forsterite (colorless) Mg 2 and fayalite (black) Fe 2. It is usually found in the form of granular aggregates or individual grains embedded in rocks.

    Color yellow-green, olive to black. Varieties containing little iron are used to make refractory bricks; peridot (yellow-green variety) is a precious stone.

    Chain and ribbon silicates and aluminosilicates. The minerals of the pyroxene group have a chain structure, and the amphibole group has a ribbon structure. Minerals of the amphibole group are characterized by long-columnar, needle-shaped or fibrous hexagonal crystals.

    Augite (Ca,Na) (Mg,Fe 2+,AlFe 3+) [(Si,Al) 2 O 6 ] found in crystalline aggregates. Color greenish black and black; glass shine.

    One of the most common minerals of the amphibole group is hornblende. (Ca,Na) 2 (Mg,Fe 2+) 4(Al,Fe 3+) (OH) 2 [(Si,Al) 4 O 11 ] 2. Its properties are close to augite, differing in the shape of the crystals and the relative position of the cleavage planes, as well as slightly lower density.

    Sheet (layered) silicates and aluminosilicates include a large number of minerals, many of which are rock-forming igneous, metamorphic and clayey sedimentary rocks. They have very perfect cleavage in one direction, parallel to the “sheets” of the crystalline structure, and low hardness.

    The most common minerals of this structural group are micas, grains of which are found in many igneous and metamorphic rocks; in the veins, individual mica crystals reach a cross section of several square meters. Origin igneous, hydrothermal, metamorphic.

    Biotite K(Mg,Fe) 3 (OH,F) 2. Color black, brown, sometimes greenish; glassy luster, sometimes pearlescent; like all micas, the leaves separated along the cleavage are elastic.

    Muscovite 3KAl 2 (OH) 2 in many properties it is close to biotite, but has an almost colorless color with a light pink or gray tint, and is transparent in thin leaves. It is used in the electrical industry, radio engineering, instrument making, for the production of fire-resistant building materials, paints, lubricants, etc.

    Talc Mg3(OH)2 forms crystalline aggregates, less often individual large crystals and their intergrowths. Color white, light green; the luster is glassy, ​​pearlescent, matte in dense fine-grained aggregates; leaflets separated by cleavage, flexible, inelastic (greasy to the touch). Widely used as a fireproof material, in the manufacture of insulators, in perfumery, etc.

    Serpentine (coil) Mg6(OH)8 usually occurs in the form of dense cryptocrystalline varieties. The fine-fiber variety is called chryso-asbestos. The color is light green, yellow-green to black, often spotted, in chryso-asbestos it is golden, individual fibers are white; The luster is glassy, ​​greasy, in chryso-asbestos it is silky. Chryso-asbestos is used to make fire-resistant and heat-insulating materials.

    TO leaf silicates refers to a number of minerals of sedimentary origin, formed during the weathering of predominantly igneous and metamorphic rocks. They make up the bulk of clayey rocks. Of these minerals, the most widespread is kaolinite Al 4 (OH) 8, which forms earthy aggregates. White color; the aggregates have a matte shine; earthy fracture; (feels greasy to the touch); easily absorbs moisture, when wet, it becomes plastic. Used in ceramic production, construction, paper industry, etc.

    From frame aluminosilicates Let's look at the minerals of the feldspar group.

    Minerals of the feldspar group are widespread in the earth's crust, making up about 50% of it. They are the rock-forming materials of many igneous and metamorphic rocks. Large crystals form in cracks. All feldspars are characterized by perfect or average cleavage in two directions. According to the chemical composition, feldspars are divided into two subgroups: 1) potassium (calinate, or alkaline) feldspars; 2) calc-sodium (calcium-sodium) feldspars, or plagioclases, representing a continuous isomorphic series Na and Ca.

    Of the first subgroup, orthoclase is the most common K[A1Si 3 O 8 ]. Color ranges from colorless, white, light gray to various shades of pink and red-yellow; cleavage in two directions. A mineral of the same composition, but crystallizing differently, is called microcline. In terms of external features, microcline is indistinguishable from orthoclase, and only its bluish-green variety - amazonite - is easily distinguished in color from other feldspars.

    Potassium feldspars (especially microcline) from pegmatite veins are used in the ceramic and glass industries.

    The subgroup of plagioclases includes minerals representing an isomorphic series. Among plagioclases, according to the amount of silicon oxide, acidic, intermediate and basic minerals are distinguished (Table 1).

    Plagioclases are similar in properties to each other and are usually not separated macroscopically. The exception is Labradorite, in which blue and green tints - iridescence - are clearly visible on a gray background.

    Plagioclases differ little macroscopically from potassium feldspars. Sometimes they can be distinguished by color: plagioclases are predominantly white, gray, greenish-gray, potassium feldspars are white, light gray, pink and yellow in various shades. There is also a difference in angle between the cleavage planes.

    Table 1

    Table of minerals of the isomorphic series of plagioclases