The mass of the Earth is 5.98 X 10 24 kg, i.e. about 6 thousand trillion tons, and its average density is 5.52 g/cubic. cm. At the same time, the average density of the outer layers of the earth's crust is half as much.
Comparing these figures, it is necessary to come to the conclusion that the interior of our planet must have a density of at least 8.37.
In the center of the Earth, the density reaches 17.2 g/cubic. cm at a pressure of 3 million atm and that it changes with a particularly sharp jump (from 5.7 to 9.4) at a depth of 2900 km, and then at a depth of 5 thousand km. The first jump allows us to identify a dense core in the globe, and the second - to subdivide this core into outer (2900-5000 km) and inner (from 5 thousand km to the center) parts.
It is most natural to think that such a high density of the central parts is due to the enormous pressures existing in the depths of the Earth, as a result of which the matter there is in a state of extremely high compression. This explanation is now gaining more and more supporters. Until the pressure in the Earth reaches a certain critical limit, the density changes gradually; when this limit (apparently 1.3 million atm) is reached, the substance jumps into a denser “metal-like” phase.
Another explanation comes down to the assumption that the interior of the Earth consists of substances of greater specific gravity than the earth's crust, mainly metals. Since the density and hardness of the internal parts of the Earth differ relatively little from the density and hardness of iron under ordinary physical conditions, most scientists are of the opinion that the earth’s core is built of iron with an admixture of nickel. Thus, the second hypothesis postulates the separation of the Earth into shells that differ sharply in their chemical composition; the first, without denying the known differentiation of matter by specific gravity, sees the main reason for the change in the density of matter inside the Earth in physical conditions (increasing pressure) and completely denies the existence of a metallic core. The larger the size of the planet, the higher the average density of planets: Mercury 3.8 g/cubic. cm, Mars 3.93, Earth 5.52. This indicates the possibility of significant compaction of the substance under the influence of increasing pressure.
Seismology, the science of earthquakes, provides especially important services in the study of the deep interior of the globe. Seismic waves in the hands of modern geophysicists have become a kind of rays, as if shining through our planet and allowing us to draw certain conclusions about its internal state and structure.
An earthquake is the result of internal stresses in the earth's substance, leading to the rupture of masses and their displacement. The displacement may be very small, but the elastic waves generated by it propagate in the body of the Earth over enormous distances from the place of their origin, called the source. The center of gravity of a seismic source is called the hypocenter. The action of waves will affect us primarily at that point (or rather region) of the earth's surface that is closest to the source - at the so-called epicenter, lying on the same vertical as the hypocenter.
The elastic wave is spherical. The radii of the sphere, i.e., the trajectories of wave propagation, are called seismic rays.
During an earthquake, three types of waves arise:
1) longitudinal waves (P), can occur in any body - solid, liquid and gaseous; resemble sound waves; move faster than all other waves generated by an earthquake;
2) transverse waves (S), moving slower than longitudinal ones; resemble light waves; are shear waves that can arise and propagate only in a solid medium;
3) even slower surface waves (L) - a complex group of waves that are formed only in the surface parts of the earth’s crust, and attenuate at depth; starting from the epicenter, they cause strong displacements and destruction on the earth's surface.
All these waves diverge from the seismic source in different ways, as a result of which at a station remote from the epicenter their arrival is recorded at different times. Long L waves arrive later, since they propagate only along the periphery of the Earth. The P and S waves that penetrate the Earth's body at great depths arrive earlier, with the faster longitudinal waves being recorded first (P - primae - the first), and then the slower transverse waves (S - secundae - the second).
If the body of the Earth were homogeneous, the seismic rays of the P and S waves would be straight lines. A gradual increase in the density of the Earth with depth would give concave trajectories, convexly facing the inside of the Earth. If the density of the Earth changes abruptly with depth, then in these concave curves there should be breaks at the boundaries of media with different densities, not to mention partial reflection of waves. It is the latter picture that we observe.
The study of seismic wave velocities, their nature and trajectories leads to the following conclusions:
1) when longitudinal and transverse waves pass through the body of the Earth, the speeds of these waves change, which indicates changes in the properties of the medium they pass through;
2) the speeds change in jumps, which means that the properties of the medium also change in jumps;
There are essentially two sharp changes in velocities: at a depth of 60 km and at a depth of 2900 km. In other words, only the outer layer (the earth’s crust) and the inner core are clearly separated. In the intermediate belt between them, as well as inside the core, there is only a change in the rate of increase in speeds.
It is also clear that the Earth is in a solid state down to a depth of 2900 km, since transverse elastic waves, which are the only ones that can arise and propagate in a solid medium, freely pass through this thickness. The passage of transverse waves through the core was not observed, and this gave reason to consider it liquid. However, the latest calculations by M. S. Molodensky show that although the shear modulus in the core is small, it is still not equal to zero (as is typical for a liquid) and, therefore, the Earth’s core is closer to a solid state than to a liquid state. Of course, in this case, the concepts of “solid” and “liquid” cannot be identified with similar concepts applied to the aggregate states of matter on the earth’s surface: high temperatures and enormous pressures prevail inside the Earth, which do not exist in the landscape shell.
There is no unanimous opinion about the chemical composition of the inner parts of the planet, since it is very difficult to talk about the chemical composition of a substance, essentially relying only on ideas about changes in its density.
The earth's crust consists predominantly of granites; sedimentary rocks are of subordinate importance in it. Under the granite shell, the existence of a layer similar in composition to basalt or peridotite is assumed. At relatively shallow depths, where the temperature and pressure are quite high, solid rocks have the property of plasticity, that is, when subjected to pressure, they are able to change their shape and maintain this change in shape after the pressure is removed.
The granite shell, in which silicon (Si) and aluminum (Al) play a huge role, is called “sialic”, or simply “sial”. Its specific gravity is on average 2.7-2.8. It is not continuous and is characterized by variable thickness: in Western Europe and North America 26-28 km, in the Caucasus 50 km, in the Tien Shan 84 km, in the Atlantic Ocean up to 18 km; in the central parts of the Pacific there is no sial at all. Both the discontinuity of distribution and the different thickness equally argue against the fact that the granite shell is the result of the solidification of the initially molten earth's surface, i.e., “zhora” in the proper sense of the word: a continuous sialic shell of the same thickness should have been formed from the melt.
The basalt layer underlying the granite shell, where, in addition to silicon and aluminum, magnesium also plays an important role, is usually abbreviated as “sima” (silicon + magnesium). This shell, the specific gravity of which is 3.2-3.3, is already solid. In the deep places of the Pacific and Atlantic oceans, the sima either directly forms the very bottom, being covered by a small thickness of sea soil and water, or is separated from the water by a thin (about 5 km) sial crust.
How can one explain the separation of the Earth into at least two concentric spheres enclosing a dense core?
The Earth arose as a cold body from a gradually expanding clot of cosmic dust and was initially homogeneous in its composition in the sense that its substance was a disordered mixture of particles of different specific gravity. When the planet reached a certain size, physicochemical and gravitational differentiation of matter began in it, i.e., a very slow descent of heavier elements deeper into the depths and lifting of lighter ones upward. At depth, the speed of this process was less than in the upper layers, since the viscosity of the substance, under the influence of ever-increasing pressure, increases with depth. One must therefore think that the separation of the so-called earth’s “crust” and the separation of the core are due to significantly different reasons. The core arose through an abrupt compaction of matter when the pressure inside the growing planet reached a certain critical value. According to B. Yu. Levin, this could only happen after the mass of the Earth grew to 0.8 of its modern mass; The formation of the core was accompanied, due to a decrease in the volume of the central parts of the planet, by a lowering of the Earth's surface by approximately 100 km. As for the surface layers, here differentiation proceeded more easily and, moreover, in its purest form: lighter acidic components separated from the homogeneous mass of basaltic composition and floated to the top. The emergence of the core narrowed the scope of differentiation: its pressure-compacted substance largely lost the “need” (and physical ability) to rise to higher levels beyond the core. This alone speaks against the assumption that the nucleus can consist of any one, almost perfectly “prepared” substance (for example, iron). Apparently, it is even much less differentiated than the overlying layers.
Good evidence of differentiation can be found in the eruption patterns of modern volcanoes. The last eruption of Hekla began on March 29, 1947 and lasted 13 months, and the lava of the initial phase of the eruption consisted of more acidic products (59% SiO 2) than the lava of the last phase (54% SiO 2 - basalt). Obviously, the more acidic lava came from the upper parts of the magma basin, the main one - from the deeper ones. This indicates that over the hundred years that have passed since the previous eruption (1845), in the magma chamber, which was in a calm state, the lava seemed to “settle”, its gravitational differentiation occurred: the more acidic light parts were at the top, the more basic, heavy ones are at the bottom.
If a volcano erupts frequently, the lava does not have time to differentiate and there is no noticeable difference in the products of the eruption. But the longer the period of rest between eruptions, the deeper the differentiation - which is why the same volcanoes in some cases emit basic lava, in others acidic.
The outpouring of liquid molten lava onto the surface does not contradict the statement that the interior of the Earth is in a solid state. Individual magma chambers can arise under the influence of heating of the earth's crust in areas of significant local concentration of radioactive elements. In addition, at great depths, where temperatures are high and under normal conditions would be sufficient to melt rocks, the latter continue to remain solid due to colossal pressures that increase the melting point. Consequently, it is enough to weaken the pressure so that the superheated substance turns into liquid and the gases contained in it begin to be carried towards the surface of the Earth. With gravitational differentiation, upward movements, i.e., the transfer of matter in areas of decreasing pressure, occur on the widest scale.
If you find an error, please highlight a piece of text and click Ctrl+Enter.
The chemical composition of the earth's crust was determined based on the results of the analysis of numerous samples of rocks and minerals that came to the surface of the earth during mountain-forming processes, as well as taken from mine workings and deep boreholes.
Currently, the earth's crust has been studied to a depth of 15-20 km. It consists of chemical elements that are part of rocks.
The most common elements in the earth's crust are 46, of which 8 make up 97.2-98.8% of its mass, 2 (oxygen and silicon) - 75% of the Earth's mass.
The first 13 elements (with the exception of titanium), most often found in the earth's crust, are part of the organic matter of plants, participate in all vital processes and play an important role in soil fertility. A large number of elements participating in chemical reactions in the bowels of the Earth lead to the formation of a wide variety of compounds. The chemical elements that are most abundant in the lithosphere are found in many minerals (mostly different rocks are made up of them).
Individual chemical elements are distributed in geospheres as follows: oxygen and hydrogen fill the hydrosphere; oxygen, hydrogen and carbon form the basis of the biosphere; oxygen, hydrogen, silicon and aluminum are the main components of clays and sands or weathering products (they mainly make up the upper part of the Earth's crust).
Chemical elements in nature are found in a variety of compounds called minerals.
7. Minerals in the earth’s crust - definition, classification, properties.
The Earth's crust is made primarily of substances called minerals - from rare and extremely valuable diamonds to various ores from which metals are obtained for our daily needs.
Determination of minerals
Commonly occurring minerals such as feldspars, quartz and mica are called rock-forming minerals. This distinguishes them from minerals, which are found only in small quantities. Calcite is another rock-forming mineral. It forms limestone rocks.
There are so many minerals in nature that mineralogists had to develop a whole system for identifying them, based on physical and chemical properties. Sometimes very simple properties, such as color or hardness, help to recognize a mineral, but sometimes this requires complex tests in the laboratory using reagents.
Some minerals, such as lapis lazuli (blue) and malachite (green), can be identified by color. But color is often deceptive because it varies quite widely among many minerals. Differences in color depend on impurities, temperature, lighting, radiation and erosion.
Classification of minerals
1. Native elements
About 90 minerals - 0.1% of the mass of the earth's crust
Gold, platinum, silver - precious metals, copper - non-ferrous metal, diamond - precious stone, graphite, sulfur, arsenic
2 . Sulfides
About 200 minerals - 0.25% of the mass of the earth's crust
Sphalerite - zinc ore, galena - lead ore, chalcopyrite - copper ore, pyrite - raw material for the chemical industry, cinnabar - mercury ore
3 . Sulfates
About 260 minerals, 0.1% of the earth's crust
Gypsum, anhydrite, barite - cement raw materials, ornamental stone, etc.
4 . Galloids
About 100 minerals
Halite - rock salt, sylvite - potassium fertilizer, fluorite - fluoride
5 . Phosphates
About 350 minerals - 0.7% of the mass of the earth's crust
Phosphorite - fertilizer
6 . Carbonates
About 80 minerals, 1.8% of the earth's crust
Calcite, aragonite, dolomite - building stone; siderite, rhodochrosite - ores of iron and manganese
7. Oxides
About 200 minerals, 17% of the mass of the earth's crust
Water, ice; quartz, chalcedony, jasper, opal, flint, corundum - precious and semi-precious stones; bauxite minerals - aluminum ores, minerals ores of iron, tin, manganese, chromium, etc.
8. Silicates
About 800 minerals, 80% of the earth's crust
Pyroxenes, amphiboles, feldspars, micas, serpentine, clay minerals are the main rock-forming minerals; garnets, olivine, topaz, adularia, amazonite - precious and semi-precious stones.
Properties
Luster is a very characteristic feature of many minerals. In some cases it is very similar to the shine of metals (galena, pyrite, arsenopyrite), in others - to the shine of glass (quartz), mother-of-pearl (muscovite). There are also many minerals that even when freshly fractured look dull, that is, they have no shine.
A remarkable feature of many natural compounds is their color. For a number of minerals it is constant and very characteristic. For example: cinnabar (mercury sulphide) always has a carmine-red color; malachite is characterized by a bright green color; cubic crystals of pyrite are easily recognized by their metallic-golden color, etc. Along with this, the color of a large number of minerals is variable. These are, for example, the varieties of quartz: colorless (transparent), milky white, yellowish-brown, almost black, purple, pink.
Minerals also differ in other physical properties. Some of them are so hard that they easily leave scratches on glass (quartz, garnet, pyrite); others are scratched themselves by fragments of glass or the edge of a knife (calcite, malachite); still others have such low hardness that they can be easily drawn with a fingernail (gypsum, graphite). Some minerals, when split, easily split along certain planes, forming fragments of regular shape, similar to crystals (rock salt, galena, calcite); others produce curved, “shell-like” surfaces when fractured (quartz). Properties such as specific gravity, fusibility, etc. also vary widely.
The chemical properties of minerals are just as different. Some are easily soluble in water (rock salt), others are soluble only in acids (calcite), and others are resistant even to strong acids (quartz). Most minerals are well preserved in air. However, a number of natural compounds are known that are easily subject to oxidation or decomposition due to oxygen, carbon dioxide and moisture contained in the air. It has also long been established that some minerals gradually change their color when exposed to light.
All these properties of minerals are causally dependent on the characteristics of the chemical composition of minerals, on the crystal structure of the substance and on the structure of the atoms or ions that make up the compounds.
Introduction…………………………………………………………………………………..2
1. Structure of the Earth……………………………………………………………….3
2. Composition of the earth’s crust………………………………………………………...5
3.1. State of the Earth………………………………………………………...7
3.2.State of the earth’s crust……………………………………………………...8
List of used literature………………………….………………10
Introduction
The Earth's crust is the outer hard shell of the Earth (geosphere). Below the crust is the mantle, which differs in composition and physical properties - it is denser and contains mainly refractory elements. The crust and mantle are separated by the Mohorovicic boundary, or Moho for short, where there is a sharp increase in seismic wave velocities. On the outside, most of the crust is covered by the hydrosphere, and the smaller part is exposed to the atmosphere.
There is a crust on most terrestrial planets, the Moon and many satellites of the giant planets. In most cases it consists of basalts. The Earth is unique in that it has two types of crust: continental and oceanic.
1. Structure of the Earth
Most of the Earth's surface (up to 71%) is occupied by the World Ocean. The average depth of the World Ocean is 3900 m. The existence of sedimentary rocks whose age exceeds 3.5 billion years serves as evidence of the existence of vast bodies of water on Earth already at that distant time. On modern continents, plains are more common, mainly low-lying ones, and mountains - especially high ones - occupy a small part of the planet's surface, as well as deep-sea depressions at the bottom of the oceans. The shape of the Earth, as is known, is close to spherical, but with more detailed measurements it turns out to be very complex, even if we outline it with a flat ocean surface (not distorted by tides, winds, currents) and the conditional continuation of this surface under the continents. The irregularities are maintained by the uneven distribution of mass in the Earth's interior.
One of the features of the Earth is its magnetic field, thanks to which we can use a compass. The Earth's magnetic pole, to which the north end of the compass needle is attracted, does not coincide with the geographic North Pole. Under the influence of the solar wind, the Earth's magnetic field is distorted and acquires a “trail” in the direction from the Sun, which extends for hundreds of thousands of kilometers.
The internal structure of the Earth is, first of all, judged by the characteristics of the passage of mechanical vibrations through the various layers of the Earth that occur during earthquakes or explosions. Valuable information is also provided by measurements of the magnitude of the heat flow emerging from the depths, the results of determinations of the total mass, moment of inertia and polar compression of our planet. The mass of the Earth is found from experimental measurements of the physical constant of gravity and the acceleration of gravity. For the mass of the Earth, the value obtained is 5.967 1024 kg. Based on a whole complex of scientific research, a model of the internal structure of the Earth was built.
The solid shell of the Earth is the lithosphere. It can be compared to a shell covering the entire surface of the Earth. But this “shell” seems to have cracked into pieces and consists of several large lithospheric plates, slowly moving one relative to the other. The overwhelming number of earthquakes is concentrated along their boundaries. The upper layer of the lithosphere is the earth's crust, the minerals of which consist mainly of silicon and aluminum oxides, iron oxides and alkali metals. The earth's crust has an uneven thickness: 35-65 km on the continents and 6-8 km under the ocean floor. The upper layer of the earth's crust consists of sedimentary rocks, the lower layer of basalts. Between them there is a layer of granites, characteristic only of the continental crust. Under the crust is the so-called mantle, which has a different chemical composition and greater density. The boundary between the crust and mantle is called the Mohorovic surface. In it, the speed of propagation of seismic waves increases abruptly. At a depth of 120-250 km under the continents and 60-400 km under the oceans lies a layer of mantle called the asthenosphere. Here the substance is in a state close to melting, its viscosity is greatly reduced. All lithospheric plates seem to float in a semi-liquid asthenosphere, like ice floes in water. Thicker sections of the earth's crust, as well as areas consisting of less dense rocks, rise relative to other sections of the crust. At the same time, additional load on a section of the crust, for example, due to the accumulation of a thick layer of continental ice, as happens in Antarctica, leads to a gradual subsidence of the section. This phenomenon is called isostatic equalization. Below the asthenosphere, starting from a depth of about 410 km, the “packing” of atoms in mineral crystals is compacted under the influence of high pressure. The sharp transition was discovered by seismic research methods at a depth of about 2920 km. Here begins the earth's core, or, more precisely, the outer core, since at its center there is another one - the inner core, the radius of which is 1250 km. The outer core is obviously in a liquid state, since transverse waves, which do not propagate in a liquid, do not pass through it. The origin of the Earth's magnetic field is associated with the existence of a liquid outer core. The inner core appears to be solid. At the lower boundary of the mantle, the pressure reaches 130 GPa, the temperature there is no higher than 5000 K. In the center of the Earth, the temperature may rise above 10,000 K.
2. Composition of the earth's crust
The earth's crust consists of several layers, the thickness and structure of which vary within the oceans and continents. In this regard, oceanic, continental and intermediate types of the earth's crust are distinguished, which will be described further.
Based on their composition, the earth's crust is usually divided into three layers - sedimentary, granite and basalt.
The sedimentary layer is composed of sedimentary rocks, which are the product of destruction and redeposition of material from the lower layers. Although this layer covers the entire surface of the Earth, it is so thin in places that one can practically speak of its discontinuity. At the same time, sometimes it reaches a power of several kilometers.
The granite layer is composed mainly of igneous rocks formed as a result of the solidification of molten magma, among which varieties rich in silica (acidic rocks) predominate. This layer, which reaches a thickness of 15-20 km on continents, is greatly reduced under the oceans and may even be completely absent.
The basalt layer is also composed of igneous material, but it is poorer in silica (basic rocks) and has a higher specific gravity. This layer is developed at the base of the earth's crust in all areas of the globe.
The continental type of the earth's crust is characterized by the presence of all three layers and is much thicker than the oceanic one.
The earth's crust is the main object of study of geology. The earth's crust consists of a very diverse range of rocks, consisting of equally diverse minerals. When studying a rock, first of all, its chemical and mineralogical composition is examined. However, this is not enough to fully understand the rock. Rocks of different origins and, consequently, different conditions of occurrence and distribution may have the same chemical and mineralogical composition.
The structure of a rock is understood as the size, composition and shape of the mineral particles composing it and the nature of their connection with each other. Different types of structures are distinguished depending on whether the rock is composed of crystals or an amorphous substance, what the size of the crystals is (whole crystals or fragments of them are part of the rock), what the degree of rounding of the fragments is, whether the mineral grains forming the rock are completely unrelated to each other or they are soldered together with some kind of cementing substance, directly fused with each other, sprouted each other, etc.
Texture refers to the relative arrangement of the components that make up the rock, or the way they fill the space occupied by the rock. Examples of textures can be: layered, when the rock consists of alternating layers of different composition and structure, schistose, when the rock easily breaks up into thin tiles, massive, porous, solid, bubbly, etc.
The form of occurrence of rocks refers to the shape of the bodies they form in the earth's crust. For some rocks these are layers, i.e. relatively thin bodies bounded by parallel surfaces; for others - cores, rods, etc.
The classification of rocks is based on their genesis, i.e. method of origin. There are three large groups of rocks: igneous, or igneous, sedimentary and metamorphic.
Igneous rocks are formed during the solidification of silicate melts located in the depths of the earth's crust under high pressure. These melts are called magma (from the Greek word for “ointment”). In some cases, magma penetrates into the thickness of the underlying rocks and solidifies at a greater or lesser depth, in others it solidifies, pouring out onto the surface of the Earth in the form of lava.
Sedimentary rocks are formed as a result of the destruction of pre-existing rocks on the Earth's surface and the subsequent deposition and accumulation of the products of this destruction.
Metamorphic rocks are the result of metamorphism, i.e. transformation of pre-existing igneous and sedimentary rocks under the influence of a sharp increase in temperature, an increase or change in the nature of pressure (change from confining pressure to oriented pressure), as well as under the influence of other factors.
3.1. State of the Earth
The condition of the earth is characterized by temperature, humidity, physical structure and chemical composition. Human activities and the functioning of flora and fauna can improve or worsen the state of the earth. The main processes of impact on land are: irreversible withdrawal from agricultural activities; temporary seizure; mechanical impact; addition of chemical and organic elements; involvement of additional territories in agricultural activities (drainage, irrigation, deforestation, reclamation); heating; self-renewal.
3.1. Condition of the earth's crust
Recently, a very complex picture of the distribution of compressive and tensile stress fields has been observed, identified by the Chinese geologist H.S. Liu (1978) and associated with the interaction of different sized crustal plates, which causes the formation of strike-slip faults in which the edges of the plates slide past each other. According to calculations by P.N. Kropotkin, areas of the earth's crust affected by tension do not exceed 2% of the total area, and the rest of it is in a state of compression.
The global picture of the stressed state of the earth’s crust, revealed through the efforts of researchers from different countries in recent decades, has given a lot to understanding the tone of the lithosphere, as S.I. figuratively noted. Sherman and Yu.I. Dneprovsky (1989). This tone has a direct impact on the geological processes occurring at the present time, and primarily on seismological ones, which allows us to raise the question of long-term earthquake forecasts.
What is the reason for the almost universal compression observed in the earth's crust? One possible explanation is to recognize a short-term decrease in the Earth's radius, which provides the compression effect. In order to prove a change in the Earth's radius, accurate data on variations in gravity, fluctuations in the Earth's rotation rate, and Chandler pole wobbles are needed. Satisfactory data on these issues are currently insufficient, and, therefore, the possibility of a reduction in the radius of the Earth is still considered a hypothesis.
There are methods for identifying not only modern, but also ancient stress fields, which makes it possible to understand many geological patterns, for example, the location of ore deposits, almost always associated with stretching areas (Fig. 4). Knowing the location of such zones in past eras, it is possible to predict the search for ore minerals. The same applies to seismicity. For example, American geologists M.D. Zobak and M.L. Zoback proved that paleoseismic zones inside the North American plate were very active in historical times, although they are now dormant. A change in the stress field can cause a new activation and resumption of earthquakes.
The efforts of scientists are now aimed at drawing up special maps showing the orientation of the axes of the main stresses; in addition, it is important to isolate the components of the stress field of different ranks. Vigorous technogenic human activity: the creation of huge reservoirs, pumping out colossal volumes of gas, oil, water from the bowels of the earth, the development of deep quarries - all this disrupts the natural stress fields and the existing dynamic balance in the earth's crust, especially its upper part. Therefore, it is necessary to observe modern stress fields, including precise instrumental methods.
Bibliography
1. Alekseenko V.A. Environmental geochemistry. – M.: Logos, 2000. – 627 p.
2. Kropotkin P.N. Tectonic stresses in the earth’s crust // Geotectonics. 1996. No. 2. P. 3-5.
3. Stressed state of the earth's crust: (According to measurements in rock masses). M.: Nauka, 1973. 188 p.
4. Zhukov M.M., Slavin V.I., Dunaeva N.N. Fundamentals of Geology. – M.: Gosgeoltekhizdat, 1961.
5. Leyall Ch. Basic principles of geology or the latest changes in the earth and its inhabitants. – Translated from English, TT. I II, 1986.
Introduction
The three outer shells of the Earth, differing in phase state - the solid crust, the liquid hydrosphere and the gas atmosphere - are closely interconnected, and the substance of each of them penetrates into the boundaries of the others. Groundwater permeates the upper part of the earth's crust; a significant volume of gases is not in the atmosphere, but is dissolved in the hydrosphere and fills voids in the soil and rocks. In turn, water and small solid mineral particles saturate the lower layers of the atmosphere.
The outer shells are connected not only spatially, but also genetically. The origin of shells, the formation of their composition and its further evolution are interconnected. Currently, this connection is largely due to the fact that the outer part of the planet is covered by the geochemical activity of living matter.
The masses of the shells vary greatly. The mass of the earth's crust is estimated at 28.46 × 10 18 tons, the World Ocean - 1.47 × 10 18 tons, the atmosphere - 0.005 × 10 18 tons. Consequently, the earth's crust contains the main reserve of chemical elements that are involved in migration processes under the influence living matter. The concentrations and distribution of chemical elements in the earth's crust have a strong influence on the composition of living organisms on land and all living matter on the Earth.
Considering the problem of the composition of living matter, V.I. Vernadsky noted: “... the chemical composition of organisms is closely related to the chemical composition of the earth’s crust; organisms adapt to it.”
Chemists and petrographers since the second half of the 19th century. studied the chemical composition of rocks using methods of gravimetric and volumetric chemical analysis. Summarizing the results of numerous analyzes of rocks, F. Clark showed that eight chemical elements predominate in the earth's crust: oxygen, silicon, aluminum, iron, magnesium, calcium, potassium and sodium. This main conclusion has been repeatedly confirmed by the results of subsequent studies. The methods of chemical analysis used in the 19th century made it impossible to determine low concentrations of elements. Fundamentally different approaches were required.
A powerful impetus to the study of chemical elements with very low concentrations in the earth's crust was given by the use of a more sensitive method - spectroscopic analysis. New facts allowed V.I. Vernadsky to formulate the principle of the “omnipresence” of all chemical elements. In a report at the XII Congress of Russian Naturalists and Doctors in December 1909, he stated: “In every drop and speck of matter on the earth’s surface, as the subtlety of our research increases, we discover more and more new elements... In a grain of sand or in a drop, as in the microcosm, the general composition of the cosmos is reflected.”
The idea of the “everywhere” of chemical elements has long aroused caution even on the part of prominent scientists. This was due to the fact that elements contained in quantities below the sensitivity level of the method were not detected during the analysis. The illusion of their complete absence was created, which was reflected in the terminology. Terms arose in geochemistry rare elements(dieselteneElementen – German; rareelements – English), frequency(dieHaufigkeit – German) detection. In reality, what is happening is not the real rarity or low frequency of occurrence of the element in analyses, but its low concentration in the samples being studied, which cannot be determined by insufficiently sensitive analytical methods.
The low sensitivity of the method often did not make it possible to determine the amount of an element, but only to state the presence of its “traces”. Since then, the term has been widely used in the geochemical literature? used by V.M. Goldschmidt and his colleagues in the 1930s: trace elements(dieSpurelemente – German; traceelements – English; deselementstraces – French).
As a result of the efforts of scientists from different countries in the 20s. XX century a general idea of the composition of the earth's crust has emerged. Average values of the relative content of chemical elements in the earth's crust and other global and cosmic systems, the famous geochemist A.E. Fersman suggested calling Clarks in honor of the scientist who charted the path to quantifying the distribution of chemical elements.
Clarke is a very important quantity in geochemistry. Analysis of clarke values allows us to understand many patterns of distribution of chemical elements on Earth, in the Solar System and in the part of the Universe accessible to our observations. The Clarke chemical elements of the earth's crust differ by more than ten mathematical orders of magnitude. Such a significant quantitative difference should be reflected in the qualitatively different role of the two groups of elements in the earth’s crust. This is most clearly manifested in the fact that the elements of the first group, contained in relatively large quantities, form independent chemical compounds, while the elements of the second group with small clarkes are predominantly dispersed, scattered among the chemical compounds of other elements. The elements of the first group are called the main ones elements of the second – absent-minded. Their synonyms in English are minorelements, rareelements, the most commonly used synonym is traceelements. The conditional boundary between groups of major and trace elements in the earth's crust can be 0.1%, although the clarkes of most trace elements are much smaller and are measured in thousandths and smaller fractions of a percent. The concept of the state of dispersion of chemical elements, as well as their “ubiquity”, was introduced into science by V.I. Vernadsky.
The complete chemical composition of the upper, so-called granite, layer of the continental block of the earth's crust is given in Table. 1.1.
Table 1.1 Clarks of chemical elements of the granite layer of the continental crust
| Chemical element | Atomic number | Average content, 1 × 10 -4 % | Chemical element | Atomic number | Average content, 1 × 10 -4 % |
| ABOUT | 8 | 481 000 | Mg | 12 | 12000 |
| Si | 14 | 399 000 | Ti | 22 | 3300 |
| A1 | 13 | 80 000 | H | 1 | 1000 |
| Fe | 26 | 36000 | P | 15 | 800 |
| TO | 19 | 27000 | F | 9 | 700 |
| Sa | 20 | 25000 | Mn | 25 | 700 |
| Na | 11 | 22000 | Va | 56 | 680 |
| S | 16 | 400 | Eg | 68 | 3,6 |
| WITH | 6 | 300 | Yb | 70 | 3,6 |
| Sr | 38 | 230 | Hf | 72 | 3,5 |
| Rb | 37 | 180 | Sn | 50 | 2,7 |
| Cl | 17 | 170 | And | 92 | 2,6 |
| Zr | 40 | 170 | Be | 4 | 2,5 |
| Xie | 58 | 83 | Br | 35 | 2,2 |
| V | 23 | 76 | Ta | 73 | 2,1 |
| Zn | 30 | 51 | As | 33 | 1,9 |
| La | 57 | 46 | W | 74 | 1,9 |
| Yr | 39 | 38 | Ho | 67 | 1,8 |
| Cl | 24 | 34 | Tl | 81 | 1,8 |
| Nd | 60 | 33 | Eu | 63 | 1,4 |
| Li | 3 | 30 | Tb | 65 | 1,4 |
| N | 7 | 26 | Ge | 32 | 1,3 |
| Ni | 28 | 26 | Mo | 42 | 1,3 |
| Cu | 29 | 22 | Lu | 71 | 1,1 |
| Nb | 41 | 20 | I | 53 | 0,5 |
| Ga | 31 | 18 | Tu | 69 | 0,3 |
| Pb | 82 | 16 | In | 49 | 0,25 |
| Th | 90 | 16 | Sb | 51 | 0,20 |
| Sc | 21 | 11 | Cd | 48 | 0,16 |
| IN | 5 | 10 | Se | 34 | 0,14 |
| Sm | 62 | 9 | Ag | 47 | 0,088 |
| Gd | 64 | 9 | Hg | 80 | 0,033 |
| Pr | 59 | 7,9 | Bi | 83 | 0,010 |
| Co | 27 | 7,3 | Au | 79 | 0,0012 |
| Dy | 66 | 6,5 | Those | 52 | 0,0010 |
| Cs | 55 | 3,8 | Re | 75 | 0,0007 |
For the formation of any chemical compound, a concentration of the starting components is required that is no less than the minimum, below which the reaction is impossible. Therefore, chemical compounds of the main elements with high clarke predominate in the earth's crust. Despite the fact that the total amount of natural chemical compounds is minerals – is 2-3 thousand species, the number of minerals that form common rocks is small. More than 80% of the mass of the earth's crust is represented by silicates of aluminum, iron, calcium, magnesium, potassium and sodium; about 12% is silicon oxide. All these minerals have a crystalline structure, which determines the general features of the crystal chemistry of the earth’s crust.
V.M. Goldschmidt showed that the silicate composition and crystalline structure of the earth's crust are very important for the distribution of minor, trace elements. According to Goldschmidt's concept, in crystal chemical structures, ions behave like hard spheres (hard balls). Therefore, the radius of each ion is considered as a constant value.
The main feature of ions in crystal chemical structures is that the radii of negatively charged ions (anions) are much larger than the radii of positively charged ions (cations). Let's imagine anions in the form of large balls, and cations in the form of small ones. Then the model of a crystalline substance with an ionic type of bond will be a space filled with tightly adjacent large balls - anions, between which small balls - cations - should be placed. According to Goldschmidt's ideas, this framework plays the role of a kind of geochemical filter that promotes the differentiation of chemical elements based on the size of their ions. A specific crystal chemical structure cannot include any elements that have the required valence, but only those whose ions have the appropriate radius size.
The formation of common minerals is accompanied by a kind of sorting of trace elements. To explain this process, let's turn to a common mineral - feldspar. Its crystal chemical structure is formed by groups consisting of three silicon cations and one aluminum, each of which is associated with four oxygen anions. The group as a whole is a complex anion, with eight oxygen ions, three silicon and one aluminum. This creates a single negative charge, which is balanced by the monovalent potassium cation. As a result, there is a three-chamber structure, the composition of which corresponds to formula K.
The radius of the potassium ion is 0.133 nm. Its place in the structure can only be taken by a cation with a similar radius. This is the divalent barium cation, the radius of which is 0.134 nm. Barium is less common than potassium. It is usually present as a minor impurity in feldspars. Only in special cases is its significant concentration created and the rare mineral celsian (barium feldspar) is formed.
Similarly, in common minerals and rocks, chemical elements are selectively retained, the concentration of which is not so high for the formation of independent minerals. The mutual substitution of ions in the crystal structure due to the proximity of their radii is called isomorphism. This phenomenon was discovered at the beginning of the 19th century, but its significance for the global differentiation of trace chemical elements was established only a century later.
As a result of isomorphism, trace elements are naturally concentrated in certain minerals. Feldspars serve as carriers of barium, strontium, and lead; olivines – nickel and cobalt; zircons – hafnium, etc. Elements such as rubidium, rhenium, and hafnium do not form independent compounds in the lithosphere and are completely dispersed in the crystal chemical structures of host minerals.
Isomorphic substitutions are not the only form of finding scattered elements. The phenomenon of scattering in the earth's crust manifests itself in different forms at different levels of dispersion.
The most coarsely dispersed form of dispersion is well-crystallized, very small (usually less than 0.01 - 0.02 mm in diameter) accessory minerals. They form mechanical inclusions in rock-forming minerals (Fig. 1.1).
Rice. 1.1 Inclusion of accessory apatite (1) and zircon (2) in feldspar grains. Transparent section, magnification 160 ´
The content of accessory elements is very small, but the concentration of scattered elements in them is so high that these elements form independent compounds. In crystalline rocks, zircon Zr, rutile, less commonly anatase and brookite, having the same composition TiO 2, apatite Ca 5 [PO 4 ] 3 F, magnetite Fe 2+ Fe 2 3+ O 4, ilmenite FeTiO 3, monazite CePO are present as accessories. 4, xenotime YPO 4, cassiterite SnO 2, chromite ECr 2 O 4 and other apatite weeds (7) and minerals of the spinel group, minerals of the columbite group (Fe, Mg) (Nb, Ta) 2 O 6, etc. The content of accessories in some rock-forming minerals, especially in mica, is quite noticeable.
In some minerals, mainly among sulfides and similar compounds, so-called solid solution decomposition structures are widespread - small separations of an impurity mineral in the substance of the host mineral. Examples of these include “emulsion dissemination” of chalcopyrite CuFeS 2 and frame Cu 2 FeSnS 4 in ZnS sphalerite, thin lamellar segregations of ilmenite FeTiO 3 in magnetite Fe 2+ Fe 2 3+ O 4 , and small segregations of silver minerals in galena PbS. As a result, lead sulfide contains a noticeable admixture of silver, copper sulfide contains an admixture of tin, and magnetite contains an admixture of titanium.
The use of a polarizing microscope and transparent sections made it possible to detect in minerals not only solid inclusions, but also micro-cavities filled with the remains of solutions from which crystallization took place (Fig. 1.2).
Rice. 1.2. Microcavities in quartz: 1 – sylvite crystal; 2 – halite crystal; 3 – gas bubble; 4 – liquid phase. Transparent section, magnification 900 ´
This phenomenon, first specifically considered in 1858 by the founder of optical petrography G. Sorbi, has now been comprehensively studied. Microcavities in minerals usually contain liquid and gas phases, sometimes with small crystals added to them. The problem of liquid inclusions was thoroughly analyzed by W. Newhouse, who noted the presence of heavy metals in liquids (up to several percent).
Some of the admixture of trace elements, easily extracted from finely ground monomineral samples, is associated precisely with liquid inclusions. N.P. Ermakov (1972), having studied microinclusions from fluorite, found in them n×10 -1% zinc, manganese, n×10 -2% barium, chromium, copper, nickel and lead, n×10 -3% titanium. Later, other trace elements were discovered in liquid inclusions.
At the same time, careful analysis of monomineral samples and the use of electronic probing showed that all rock-forming minerals, without exception, contain trace elements in such a highly dispersed form that they cannot be detected not only using optical, but also electron microscopy. In this case, scattering of elements occurs at the level of ions and molecules. The forms of such scattering are not limited to the previously considered isomorphism phenomena. There are numerous cases of the presence of chemical elements in minerals that have no connection with isomorphism.
The results of many thousands of analyzes carried out in different countries over the past 50 years suggest that all rock-forming minerals are carriers of trace elements. It is in them that the bulk of the trace elements contained in the earth's crust is concentrated. Knowing the content of carrier minerals and the concentration of trace elements in them, it is possible to calculate the balance within a particular rock.
When studying the granites of the Tien Shan, it was discovered that quartz, despite the insignificant concentration of lead, contains more than 5% of the total mass of this metal contained in the rock (Table 1.2).
Table 1.2. Distribution of lead in minerals composing granites of the Jumgol ridge
It is impossible to assume the isomorphic occurrence of lead, zinc or other metal in the quartz structure formed by a combination of silicon and oxygen ions. Meanwhile, quartz serves as a carrier of many trace elements. A special method has been developed for assessing the potential ore content of rocks and veins based on the content of lithium, rubidium, and boron in quartz.
In an experimental study of the strength of fixation of trace metals in rock-forming minerals, it was discovered that when a finely ground mineral mass is treated with successive portions of weak acid-base solvents, a significant part of the metals is easily extracted during the first extraction, and this extraction is not accompanied by destruction of the crystallochemical structure of the minerals. With further processing, the amount of extracted metals is sharply reduced or stopped altogether. This allowed us to make the assumption that some of the scattered elements are not included in the actual crystal chemical structure, but are confined to defects in real crystals. Defects are various types of cracks, and they are so small that they cannot be detected by an optical microscope. The ease of extraction of trace metals is explained by the fact that they are bound to the surface of the carrier mineral by sorption forces. In rock-forming silicates, this form of occurrence of trace metals accounts for 10–20% of the total mass of trace metals. In particular, the loosely bound form of lead in Tien Shan granites accounts for 12 to 18% of the total mass of the trace element.
The following forms of occurrence of trace elements in the crystalline matter of the earth’s crust can be distinguished:
I. Micromineralogical forms:
1. Elements included in accessory minerals.
2. Elements contained in microscopic secretions as a result of the decomposition of solid solutions.
3. Elements found in inclusions of residual solutions. P. Non-mineralogical forms:
4. Elements sorbed by the surface of defects in real crystals.
5. Elements included in the structure of the carrier mineral according to the laws of isomorphism.
6. Elements that are in a disordered state in the structure of the carrier mineral.
The combination of the considered forms of occurrence of scattered elements varies greatly depending on many factors. Accordingly, the total content of trace elements in different parts of the earth's crust also changes.
3. Features of chemical distribution elements in the earth's crust
The variation in element content in different samples is due to many independent reasons. When the distribution of a quantity is determined by a sufficiently large number of approximately resultant and mutually independent causes, then it obeys the so-called normal Gauss law. Its graphical expression is a curve with symmetrical branches on both sides of the maximum ordinate. With a normal distribution, the most probable value is arithmetic mean x, which coincides with the most frequently occurring values – fashion. The extension of a symmetrical curve along the abscissa axis, i.e. the spread of values up and down the fashion is characterized by standard deviation A.
A normal distribution can also appear not for the value itself, but for its logarithm (logarithmically normal, or lognormal, distribution law). In this case, the mode coincides with the geometric mean, and the spread of values is characterized by the logarithm a.
In 1940 N.K. Razumovsky empirically discovered that the content of metals in ores corresponds to a lognormal distribution. L.X. Arena in 1954, having processed extensive material, independently of Razumovsky, established that the distribution of trace elements in igneous rocks is approximated by a logarithmically normal law. Numerous facts indicate that the distribution of elements with high clarkes usually obeys the normal law, while those of scattered elements obey the lognormal law. This once again confirms the fundamental difference between the main and scattered elements.
The high variability of low-clark elements is associated with their ability to reach a high degree of concentration. The maximum degree of concentration of the main elements is 10 - 20 times relative to their clarke, and for trace elements - hundreds and thousands of times more. For example, in ores from industrial deposits, the concentration of lead, nickel, tin, chromium is 1000× P.
Speaking about the huge masses of heavy metals concentrated in ore deposits, it should be remembered that these masses are an insignificant part of the total amount of metals scattered in the earth’s crust. In particular, the global reserves of zinc, copper, lead, and nickel ores constitute only thousandths of a percent of the masses of these metals scattered in the upper kilometer layer of the continents' crust.
Ore deposits are connected to the surrounding rocks by gradual transitions. Ore bodies are located, as it were, in a case of gradually decreasing concentration of metals. Such formations are called scattering halos Primary, syngenetic ore aureoles arise simultaneously with ore bodies and as a result of the same processes. They have a varied configuration, depending on the geological structure, the composition of the host rocks and the conditions of ore formation.
In ores, along with one or more main ore-forming elements, there are accompanying elements, the concentration of which is also increased, but not as much as the main ones. Satellite elements often form isomorphic substitutions of the main ones. For example, zinc ores constantly contain cadmium, and in smaller quantities indium, gallium, and germanium. Copper-nickel ores contain a significant admixture of cobalt, and smaller amounts of selenium and tellurium. All accompanying elements are also dispersed around the ore bodies. Possessing unequal geochemical mobility, they form transition zones of different lengths. As a result, the composition and structure of scattering halos are very complex.
The average content of a chemical element is the norm - geochemical background– for a given type of rock in a certain area. Stand out against the geochemical background geochemical anomalies– areas of rocks with an increased concentration of trace elements. If they are associated with ore deposits, then these are dispersion halos. If the metal concentrations do not reach the ore standard, then such anomalies are called false. Using statistical processing of mass analytical data, it is possible to detect regular changes in the value of the geochemical background in space and identify geochemical provinces. Within provinces, rocks of the same type have consistent statistical parameters, primarily the average content of one or more trace elements. The average content of some elements in rocks of the same type from different geochemical provinces can vary greatly (several times). At the same time, the chemical composition of these rocks, determined by the content of the main elements, remains the same or has very slight differences. For example, in granites from different provinces, which have almost the same amount of silicon, aluminum, iron, potassium, the content of tin, lead, molybdenum, and uranium can differ by 2–3 times.
The presented material indicates the uneven distribution of trace elements in the earth's crust. Therefore, along with the definition of clarks, i.e. the average concentration of elements in the earth’s crust as a whole, it is necessary to take into account their ability to concentrate or disperse in various objects - different types of rocks or in rocks of the same type, but located in different geochemical provinces, in ores, etc. To quantitatively assess the heterogeneity of chemical elements in the earth’s Kore, V.I. Vernadsky introduced a special indicator - clarke concentration Kc. Its numerical value characterizes the deviation of the element content in a given volume from the clarke:
K K = A/K,
Where A– content of a chemical element in a rock, ore, mineral, etc.;
TO- clarke of this element in the earth's crust. If the clarke concentration is greater than one, this indicates enrichment in the element; if less, it means a decrease in its content compared to data for the earth’s crust as a whole.
Changes in the concentration of chemical elements in space, deviations from the global or local geochemical norm Mb1 __ are not isolated cases, but a characteristic feature of the geochemical structure of the earth's crust. This is very important for the composition of photosynthetic organisms on land, which form the bulk of the mass of living matter on the Earth.
Literature
1. Alekseenko V.A. Environmental geochemistry. – M.: Logos, 2000. – 627 p.
2. Arena L. X. Distribution of elements in igneous rocks // Chemistry of the Earth’s crust. – M.: Nauka, 1964. – T. 2. – P. 293–300.
3. Vernadsky V.I. Essays on geochemistry // Izbr. cit.: In 5 vols. – M.: Publishing House of the USSR Academy of Sciences, 1954. – T. 1. – P. 7–391.
4. Voitkevich G.V., Miroshnikov A.E., Povarenykh A.S., Prokhorov V.G. A short guide to geochemistry. – M.: Nedra, 1977. – 183 p.
5. Goldshmit V.M. Principles of distribution of chemical elements in minerals and rocks // Collection of articles. Art. on geochemistry of rare elements. – M. – L.: GONTI NKTP USSR, 1930. – P. 215–242.
6. Dobrovolsky V.V. Geography of trace elements. Global dispersion. – M.: Mysl, 1983. – 269 p.
7. Perelman A.I. Geochemistry. – M.: Higher. school, 1989. – 528 p.
8. Ronov A.B., Yaroshevsky A.A. A new model of the chemical composition of the earth’s crust // Geochemistry. – 1976. – No. 12. – S. 1763–1795.
Remember
- What do you know about the internal structure of the Earth? What rocks do you know? By what properties do they differ?
The interior of the Earth is a mysterious and much less accessible world than the space surrounding our planet. Such a device has not yet been invented in which it would be possible to penetrate into the depths of the planet. The world's deepest mine has a depth of 4 km, the deepest borehole on the Kola Peninsula is 12 km. This is only 1/500th of the radius of the Earth!
However, people have learned to “look” into the depths of the earth. The main method of studying them is seismic (from the Greek “seismos” - earthquake). From earthquakes or artificial explosions, vibrations spread in the bowels of the Earth. In substances of different composition and density they propagate at different speeds. Using instruments, specialists measure these speeds and decipher the information.
It has been established that the interior of our planet is divided into several shells: the core, the mantle and the earth’s crust (Fig. 33).
Core- the central part of the globe. It has very high pressure and temperature of 3000-4000 °C. The core consists of the densest and heaviest substance, presumably iron. The core accounts for about 30% of the Earth's mass, but only 15% of its volume. The inner solid part of the core seems to float in the outer, liquid layer. Due to this movement around the Earth, a magnetic field arises. It protects life on our planet from harmful cosmic rays. The compass needle reacts to the magnetic field.
Rice. 33. Internal structure of the Earth
According to scientists, the separation of the Earth's substance into the core, mantle and crust has occurred since the formation of the planet 4.6 billion years ago and continues to the present day. Heavier substances sink to the center of the Earth and become even more dense, while lighter substances rise upward and form the earth's crust. When the Earth's matter is redistributed, heat is released - the main source of internal energy of the Earth. When the separation of the Earth's interior is completely completed, the Earth will become a cold and dead planet. According to calculations, this could happen in 1.5 billion years.
Mantle(from the Greek “mantle” - cover, cloak) - the largest of the internal shells of the Earth. The mantle accounts for the bulk (more than 80%) and mass (almost 70%) of our planet. The mantle material is solid, but less dense than in the core. Pressure and temperature in the mantle increase with depth. At the top of the mantle there is a layer where the material is partially molten and plastic. The hard layers lying above move along this plastic layer.
Earth's crust- the thinnest outer shell of the Earth. The earth's crust accounts for less than 1% of the earth's mass. It is on the surface of the earth's crust that people live, from which they extract minerals. In different places, the earth's crust is pierced by numerous mines and boreholes. Millions of samples taken from them and from the Earth's surface made it possible to determine the composition and structure of the earth's crust.
Feldspars make up half the mass of the earth's crust. They even received the name “field” due to their widespread distribution. They can be found everywhere: in the mountains, in the fields...
Quartz is one of the most common minerals. Colorless quartz is called rock crystal. Varieties of quartz of other colors are known: purple, yellow, brown, black.
What is the earth's crust made of? The Earth's crust is made up of rocks, and rocks are made up of minerals. (Remember what minerals you are familiar with. Where did you manage to see them?)
Minerals are natural substances with different composition, properties and external characteristics.
Minerals are distinguished by such characteristics as color, hardness, luster, transparency, and density. Minerals were formed and continue to form both in the deep layers of the earth's crust and on its surface.
Rice. 34. The most common minerals on Earth: a - feldspar; b - quartz; c - mica
People know about 3000 minerals. Most of them are rare. Rare minerals include diamond, platinum, silver, and graphite. There are only a few dozen widespread minerals that make up rocks. The most abundant minerals on Earth are feldspars, quartz, and mica (Fig. 34). Minerals form rocks.
Rocks are natural bodies composed of one or more minerals.
Mineral crystals in rock can vary in size. In many breeds they can only be seen under a microscope. Crystals of minerals are connected to each other with different strengths. Therefore, some rocks are hard and monolithic, others are porous and light, and others are loose and friable. The composition of minerals in a rock and the strength of their connection depend on the conditions in which the rock was formed. According to the conditions of formation, all rocks are divided into three large groups: igneous, sedimentary and metamorphic.
Questions and tasks
- What has more mass - the core, the mantle or the earth's crust?
- What state is the substance in the mantle? in the core?
- What is rock? How is it different from a mineral?
- Give examples of rocks and minerals that are common in your area.
