List of rocks alphabetically. Major sedimentary rocks of organic and chemical origin

Stones of organic origin - a selection of stones, photos, properties, origin

Stones born of life

They say about the stone "cold", "dead", "lifeless". But life on Earth is not much younger than the planet itself, and many of the earth's minerals are formed by living organisms. Oil, according to modern concepts, is a visible trace of the existence of microscopic unicellular plants and animals of the distant past. Coal was considered by ancient naturalists to be the brother of oil. Chalk, limestone, marble are the life products of sea creatures...

This is where the list of minerals of biogenic origin that comes to mind to the average person usually ends. However, a knowledgeable mineralogist could go on and on with the list of rocks that appeared on Earth solely due to the existence of life.

Even gemology, the science of precious stones, is ready to present an impressive list of gems, each of which was once alive. The champion of popularity among jewelry of biological nature is pearls!

Mother of pearl - half brother of pearls

It just didn't come out in shape. If a pearl is a spherical formation (or close to a sphere in shape), then it is only deposited on the walls of the shell.

The demand for mother-of-pearl has always exceeded the demand for pearls due to the low price and wide availability of the material. Pearls are rare, and there are tons of mother-of-pearl in any river. Mollusk shells, covered with a thick layer of mother-of-pearl, have been used to make buttons, combs, handles and other consumer goods for many centuries. Today there is no type of plastic that would be used as widely and actively as mother-of-pearl in the recent past.

Once palm trees grew everywhere

...because it was warm and humid. The petrified palm stem can be found in coal deposits, in shale, and in quartz deposits. It is silicates that make palm wood an aesthetically expressive stone.

It should be noted that in its botanical essence, the palm tree is a tree-like, but herbaceous plant. You can't find annual rings on palm trees! On the other hand, the longitudinal vessels, through which the nutrient juices circulated throughout the plant, are very clearly visible. They - both on the transverse and on the longitudinal cut of petrified palm wood - make up the beauty of the stone.

The soft starchy core of the palm trunk is not rich in vessels, and therefore is replaced during fossilization by a homogeneous siliceous material.

Various silicas, impregnating the trunks of flooded, covered, drowned trees in swamps, often turn unremarkable wood into a precious gem. Silicates, colored with a variety of mineral impurities, acquire an iridescent color. A chip, saw cut, and even better, a thin section often amazes with the richness of the natural palette of colors.

In this case, the layered wood structure remains, as a rule, well distinguishable. What only adds decorativeness to the most beautiful stone of biological origin.

Stromatolite jaspers

Jasper Rock Mary Ellen is located in the state of Minnesota (USA). It is famous for the fact that the main masses of rocks that make up the mountain - red jasper and silver hematite - are intertwined in unthinkable clubs and twists.

Red and black is an advantageous color combination for any artistic subject. However, stromatolites, formed from layered colonies of cyanobacteria two billion years ago, rarely turn red. Only on the American continent were found traces of the first steps of life on the planet, made by red jasper on black iron ore...

petrified corals

A polished petrified one makes you want to blow off dust particles from it - the jewelry work of nature is so fine. Cellular frameworks of marine organisms of the distant past are delicately arranged and skillfully "executed". The resemblance of fossil coral to the work of a skilled craftsman is endless!

Quartz and calcite, replacing organic tissue in fossilized corals, make jewelry durable. However, the bright colors characteristic of modern corals are not found in fossil polyps. Fiery red or transparent yellow earrings made of petrified corals are the product of handicraft "improvement".

"Sand Dollar"

"Sand dollar" in both Americas is called the skeleton of a sea urchin, classified as incorrect (such is zoological terminology). Correct hedgehogs are round echinoderms, incorrect ones are flat. They have been living on Earth for a long time, and in some places they inhabit the shelf bottom so densely that they lie on the sand like scales on the body of a crucian carp - or even in two layers.

Wrong hedgehogs have a very conditional needle-like protection, and therefore everyone who is not lazy feeds on them. Nevertheless, many of the animals that are flat as a toy saucer manage to grow a decent thickness of the skeleton, live to a natural death and please people with the sight of their skeleton - the "sand dollar". Especially highly valued are dollars "issued" millions of years ago...

Ammonites

Anyone who has been interested in the history of evolution knows about the ammonites. They - sometimes quite modest in size, sometimes under two meters in diameter - are twisted into a flat spiral, like the horns of the god Amun in one of his earthly incarnations. Ammonites are easy to find in natural screes. In some European countries, they have long been called "golden snails".

Ammonite "gold" is a layer of petrified mother-of-pearl in sealed shell chambers. The most beautiful ammonites are mined in the Canadian province of Alberta. The iridescent radiance of the polished walls of the shells surpasses the play of color in opal and labradorite.

dinosaur bone

The process of bone fossilization is extremely long, because each molecule of calcium phosphate (of which, in fact, bones are composed) must be replaced by a molecule of silicon dioxide. It takes at least two million years for a medium-sized dinosaur skeleton to turn into a precious gem!

Fortunately, something, but dinosaur bones have enough time with a large margin. For 65 million years separating us from the last animal lizards of the Earth, many tons of bones turned into colored quartz. Moreover, a considerable part of quartz took on impurities, which allowed the hitherto unattractive natural material to acquire both the look, the pattern, and the texture at a good jewelry level. Dinosaur bone cabochons are often extremely attractive!

Ivory is younger than dinosaur bones. Today, under the name of "ivory" distinguish the tusks of African and Indian elephants, fossil mammoths, walrus fangs, hippo and sperm whale teeth.

The main thing is its luxurious appearance. However, the manufacturability of the material is also important. Last but not least, artisans fell in love with ivory because of its ability to become plastic, and then harden again.

Ivory color varies. The white and blue tooth of a hippopotamus, warm shades (up to red-brown) of mammoth tusk, translucent whiteness of the tusk of a young elephant are valued.

The list of stones of biological origin can go on and on. The gallery of precious gems is replenished by the efforts of geologists, explorers, pioneers of hard-to-reach areas of the planet.

Like the glow of dawn

The first pearls people found in search of food. Oysters producing this gem are still loved by gourmets. For thousands of years, people have been admiring the radiance of pearls that have grown by the will of nature - and for several decades now we have been forcing mollusks to envelop seed grains of sand in multi-colored layers.

Today's pearls are all colors of the rainbow and even the colors of the night! But, as in the old days, this is a stone in which at least half of the mass falls on organic tissue. We examined pearls in more detail in the article, and you can be sure that this stone of biological origin has been in favor of fashionistas for the fifth millennium in a row!

Frozen sunshine...

... poetically called amber. Both honey-transparent and the most “foggy” forms of the stone really give the impression of clots of luminous substance. There are countless varieties of amber! The color range of this natural jewel ranges from milky white through all shades of yellow and red to blue and green. There are amber and black!

Every amber is a piece of fossilized resin of a tree that grew millions of years ago. There are ambers born in pine groves, and ambers that originated from the resin of tropical trees. We talked about amber in the articles: and. Now the time has come to pay attention to the trees that grew hundreds of millions of years ago, and by our time have turned into "precious stones".

"Peanut" wood

Wood with a clear structuring of the array during fossilization can also give an unexpected visual effect. Particularly interesting are the fossilized wood remains that have spent many years under water. The point, in fact, is not in the water, but in the mollusks that inhabit the reservoirs of the planet. Some of them feed on rotting wood, and in the process of obtaining food they go deep into the flooded logs, gnawing through numerous passages.

The subsequent mineralization of organics led to a striking result. The cavities gnawed (more precisely, machined) by the mealybug were filled with white quartz. The fabrics of the tree remained colored. Minerologists dubbed this kind of petrified wood "peanut forest" - for the similarity of the stone pattern with sprouting peanuts is almost one hundred percent.

Jet

However, not all plant remains of the distant past are so lucky. Jet, a mineral related to coal, is recognized as the same prehistoric wood that survived flooding in the silt layers two hundred million years ago.

Unattractive in its raw form, polished jet shines like silk velvet. The best grades of stone are distinguished by a mirror gloss and are used to make jewelry. In the recent past, a lot of haberdashery trifles were made from jet - like buttons, beads, beads. served its owners no worse than mother-of-pearl.

corals

Most of the bottom marine sediments are formed by the calcareous remains of organisms that lived in ancient times. However, corals, having won a warm place five hundred million years ago, thrive to this day.

Calcareous skeletons of corals have three and a half hundred variants of natural coloration. Polished coral is an excellent material for making jewelry. However, the user must remember: the thicker the color of the coral, the more organic matter it contains, and the more careful the subject should be treated.

Modern types of corals are different from the polyps that inhabited the earth's seas in past geological epochs. However, we can say with confidence: petrified corals are extremely beautiful and interesting!

Compressed carcasses of sea lilies

Crinoid sea lilies once so abundantly inhabited the shallow bottom of the warm seas that their calcareous cores - mostly tubular, divided into short segments - became a rock-forming element. Many of the most interesting specimens of these Proterozoic pufferfish were obtained during the construction of the Moscow metro.

However, crinoidal limestone, formed by the remains of flower-like animals three hundred million years ago, is not found under (literally) Moscow. Although this mineral is widely distributed.

Distinguishable remains of crinoids, “soldered” into the thickness of a translucent mineral, are sometimes very decorative. Such stones become a worthy decoration.

Under the sonorous name lies a beautiful mineral with an unusual history. In fact, turritella terebra is the name of a marine mollusk with a helical shell. They say that it was turitella shells that prompted the legendary Archimedes to construct a water-lifting propeller.

Turitella agate is, in fact, a scattering of shells of a mollusk of this species, which are in varying degrees of preservation, filled with hardened silicate. Many of the real turitell agates include sand, water, air bubbles.

Take a closer look at the appearance of the gem! Under the name of agate-turitella, any petrified garbage is often sold. If you do not see distinctly preserved elements of cone-spiral shells, this is a fake!

The class of carbonate rocks includes limestones, dolomites, marls and sidirite rocks. Between the first two types there is a relatively small number of transitional rocks.

The classification of rocks transitional between pure limestone and dolomite is based on the content of calcite and dolomite in them. The group of limestones or dolomites includes rocks composed of more than 50% of one of these minerals.

Among rocks transitional between pure limestones and dolomites, dolomitic and dolomitic limestones, calcareous and calcareous dolomites are distinguished.

In carbonate rocks, a significant admixture of sand and clay particles is usually observed. Pure limestones and dolomites contain an admixture of other minerals in an amount of not more than 5%.

Some dolomites contain a significant admixture of gypsum and anhydrite. Such rocks are commonly referred to as sulphate-dolomitic. There are also transitions between carbonate and siliceous rocks.

Rocks intermediate between clays and pure carbonate rocks are called marls.

The classification scheme for carbonate-argillaceous rocks according to S.G. Vishnyakov is illustrated in the figure.

Clays: 1- non-carbonate, 2- calcareous-dolomite (or dolomite-calcareous).

Clay marls: 3 - clay marl, 4 - dolomitic clay marl, 5 - calcareous-dolomitic clay marl, 6 - dolomitic clay marl.

Marls: 7 - typical, 8 - dolomite, 9 - calcareous-dolomite, 10 - dolomitic.

Limestones: 11 - clayey, 12 - dolomitic-clayey, 13 - dolomitic-clayey, 14 - pure, 15 - dolomitic, 16 - dolomitic.

Dolomites: 17 - calcareous-clayey, 18 - calcareous-clayey, 19 - clayey, 20 - calcareous, 21 - calcareous, 22 - clean.

Mineralogical and chemical composition

The main minerals that make up carbonate rocks are: calcite, which crystallizes in a trigonal syngony, aragonite, a rhombic variety of CaCO3, and dolomite, which is a double carbon dioxide salt of calcium and magnesium (CaCO 3 * MgCO 3). Recent sediments also contain powdered and colloidal varieties of calcite (druite or nadsonite, bugleite, etc.).

The determination of the mineral and chemical composition of carbonate rocks is carried out in thin sections, as well as using thermal and chemical analyzes and according to the Shcherbina method.

In the field, determined by reaction with dilute HCl. Dolomites boil only in powder.

The theoretical chemical composition of calcite and limestone ~ CaO - 56%, CO 2 - 44%, in dolomites - 22-30% CaO and 14-21% MgO.

Naturally, if clastic material is present in the rocks, then the content of SiO 2 will sharply increase (sometimes up to 26%).

Main rock types

Limestones - the color of limestones is diverse and is determined, first of all, by the nature of impurities. Pure limestones are colored white, yellowish, gray, dark gray, and sometimes black.

An important feature of limestones is their fracture, the nature of which is determined by the structure of the rock. Very fine-grained calcareous rocks with a weak cohesion of grains (for example, chalk) have an earthy fracture. Coarse-grained - have a sparkling fracture, m / s of the rock - a sugar-like fracture, etc.

For limestones, the following main types of structures can be distinguished:

Crystalline granular structure, among which several varieties are distinguished depending on the diameter of the grains: coarse-grained (grain size in diameter 0.5 mm), medium-grained (from 0.5 to 0.1 mm), fine-grained (from 0.10 to 0.05 mm), fine-grained (from 0.05 to 0.01 mm) and micro-grained (less than 0.01 mm) structures.

Organogenic structure, in which three most significant varieties are distinguished:

A). actually organogenic, when the rock consists of calcareous organic residues (without signs of their transfer), interspersed in t/z carbonate material;

b). organogenic-detrital, when crushed and often rounded organic remains are present in the rock, located among the t / s of carbonate material;

V). detritus, when the rock is composed only of crushed organic remains without a noticeable amount of heavy carbonate particles.

The clastic structure is observed in limestones formed by the accumulation of fragments arising from the destruction of older carbonate rocks. Here, as well as in some organic limestones, in addition to fragments, a calcareous cementing mass is clearly visible.

The oolitic structure is characterized by the presence of concentrically folded oolites, usually clastic grains are often present.

Sometimes oolites acquire a radially radiant structure.

Inlay and crustification structures are also observed. In the first case, the presence of crusts of a concentric structure is characteristic, filling the former large voids. In the second case, growths of elongated carbonate crystals are observed, located radially relative to the fragments or organic remains that make up the rock.

In the process of transition from sediment to rock and petrification, many limestones undergo significant changes. These changes are manifested, in particular, in recrystallization, petrification, dolomitization, ferruginization and partial dissolution with the formation of stillolites.

Varieties of limestone

Organic limestones

This is one of the most widely used varieties. They are composed of shells of benthic crinoids, algae, corals and other benthic organisms. Much less often, limestones form due to the accumulation of shells of planktonic forms.

Typical representatives of organogenic limestones are reef (biohermic), limestones, consisting largely of the remains of reef-forming organisms and living in a community of other forms.

Writing chalk.

It is one of the very peculiar representatives of calcareous rocks, which stand out sharply in their appearance. It is characterized by white color, uniform structure, low hardness and fine grain. Complicated - mainly calcium carbonate (no dolomite) with a slight admixture of clay and sand particles.

Organic residues make up most of the chalk. Among them, the remains of coccolithophorids, unicellular calcareous algae, composing 10-75% of chalk and chalk-like marls in the form of small (0.002-0.005 mm) plates, discs and tubes, are especially common. Foraminifera are found in chalk, usually in an amount of 5-6% (sometimes up to 40%). There are also shells of mollusks (mainly inocerams, less often oysters and pectinids) and a few belemnites, and in places also ammonite shells. Remains of bryozoans, sea lilies, urchins, corals and tube worms, although observed, do not serve as rock-forming elements of the chalk.

Limestones of chemical origin.

This type of limestone is conditionally separated from other types, because. in most limestones there is always some amount of calcite precipitated from the water by a purely chemical means. You can easily and quickly buy a suitcase in Moscow on the website caseplus.ru. Also here you will find many different bags and backpacks, various leather goods and just the necessary accessories.

Typical limestones of chemical origin are microgranular, devoid of organic residues and occur in the form of layers, and sometimes accumulations of concretions. Often they contain a system of small calcite veins, which form, with a decrease in the volume, initially colloidal sediments. Often there are geodes with large and well-formed calcite crystals.

Clastic limestones.

This type of limestone contains a significant admixture of quartz grains and is usually associated with sandy rocks. Clastic limestones are characterized by oblique bedding.

Clastic limestones are composed of carbonate grains of various sizes, the diameter of which is measured in tenths of a millimeter, less often several millimeters. There are also conglomerate-like limestones, consisting of large fragments. Clastic carbonate grains are usually well rounded and similar in size.

Secondary limestones.

This group includes limestones occurring in the upper part of salt domes, and limestones arising in the process of transformation of dolomites during their weathering (razdolomitization or dedolomiticization).

Broken rocks are medium- or coarse-grained limestones, dense, but sometimes porous or cavernous. They lie in the form of solid masses. In some cases, they contain lenticular inclusions of fine-grained and fine-grained dolomites, sometimes loose and soiling fingers. More rarely, they form inclusions and branching veins in the thickness of dolomites.

Dolomites

They are carbonate rocks, consisting mainly of the mineral - dolomite. Pure dolomite corresponds to the formula CaMg(CO 3) 2 and contains 30.4% CaO, 21.8% MgO and 47.8% CO 2 or 54.3% CaCO 3 and 45.7% MgCO 3 . The weight ratio of CaO:Mg is 1.39.

Dolomites usually contain less clastic impurities than limestones. Also characteristic is the presence of minerals precipitated by a purely chemical means during the formation of a sediment or arising during its diagenesis (calcite, gypsum, anhydrite, celestite, rhodochrosite, magnesite, iron oxides, less often silica in the form of opal and chalcedony, organic matter, etc.). In some cases, the presence of pseudomorphs along the crystals of various salts is observed.

In appearance, many dolomites are very similar to limestones, with which they are brought together by color and the inability to distinguish calcite from dolomite in a finely crystalline state with the naked eye.

Among the dolomites there are completely homogeneous varieties from micro-grained (porcelain-like), sometimes soiling the hands and having a conchoidal fracture, to fine- and coarse-grained varieties, composed of dolomite rhomboids of approximately the same size (usually 0.25-0.05 mm). The leached varieties of these rocks are somewhat reminiscent of sandstones in appearance.

Dolomites are sometimes characterized by vugginess, in particular due to leaching of shells, porosity (especially in natural outcrops) and fracturing. Some dolomites have the ability to spontaneous cracking. Well-preserved organic remains in dolomites are rare. Dolomites are mostly colored in light shades of yellowish, pinkish, reddish, greenish and other tones. Some dolomites are somewhat reminiscent of mother-of-pearl in their color and brilliance.

Dolomites are characterized by a crystalline granular (mosaic) structure, which is also common for limestones, and various kinds of relict structures caused by the replacement of calcareous organic residues, oolites or carbonate fragments during dolomitization. There is sometimes an oolitic, as well as an incrustation structure formed as a result of various cavities, usually in reef massifs.

For rocks transitional from limestones to dolomites, a porphyritic structure is typical, when separate large rhombohedrons of dolomite are present against the background of a finely crystalline calcite mass.

Varieties of dolomites

By origin, dolomites are divided into primary sedimentary, syngenetic, diagenetic and epigenetic. The first three types are often grouped under the name of primary dolomites, while epigenetic dolomites are also called secondary.

Primary sedimentary dolomites.

These dolomites arose in sea bays and lagoons with high salinity water due to the direct precipitation of dolomite from the water. These rocks lie in the form of well-seasoned layers, within which thin bedding is sometimes clearly expressed. Primary vugginess and porosity, as well as organic residues, are absent. Interlayering of such dolomites with gypsum is often observed. The contacts of the layers are even, slightly wavy, or gradual. Sometimes there are inclusions of gypsum or anhydrite.

The structure of primary sedimentary dolomites is uniformly microgranular. The predominant grain size is ~0.01 mm. Calcite occurs only as a minor admixture. Sometimes there is petrification, sometimes intense.

Syngenetic and diagenetic dolomites.

Among them is the predominant part of the dolomites. It is not always possible to distinguish between them. They arise due to the transformation of lime sludge.

These dolomites occur in the form of layers and lenticular deposits. They are strong rocks with uneven, rough fractures, usually with unclear layering. The structure of syngenetic dolomites is often uniformly microgranular. For diagenetic, unevenly granular is more typical (their grain diameters vary from 0.1 to 0.01 mm). Characteristic of diagenetic dolomites is also an irregularly rhombohedral or oval shape of dolomite grains, often having a concentric zonal structure. In the central part of the grains there are dark dust-like accumulations.

In some cases, gypsuming of the rock occurs. At the same time, the most permeable for solutions areas of carbonate rock (in particular, organic remains), as well as accumulations of pelitomorphic dolomite, were most easily replaced by gypsum.

Secondary (epigenetic) dolomites.

This type of dolomite is formed in the process of replacement with the help of solutions of already solid limestones, fully formed as rocks. Epigenetic dolomites usually occur in the form of lenses among unchanged limestones or contain areas of residual limestone.

Epigenetic dolomites are characterized by massiveness or indistinct layering, uneven-grained and heterogeneous structure. They are coarse and inhomogeneously porous. Near areas completely dolomitized, there are areas almost unaffected by this process. The boundary between such areas is sinuous, uneven, and sometimes passes in the middle of the shells.

Mergeli

Marl refers to rocks that are transitional between carbonate and clay, containing 25-95% CaCO 3 . Their most carbonate varieties (75-95% CaCO 3), in the case of significant compaction of the rock, are called clayey limestones.

Marls are divided into three main groups:

1. Actually marls, with a CaCO 3 content of 50-70%,

2. Lime marls, in which the content of CaCO 3 varies within 75-95%,

3. Clay marls with CaCO 3 content from 25 to 50%.

Typical marls are rock of a homogeneous structure, very soft, consisting of a mixture of clay and carbonate particles and often having a certain plasticity when wet. Usually marls are painted in light colors, but there are also brightly colored varieties - red, brown, purple (especially in red-colored strata). Thin layering is not typical for marls, but many of them occur in the form of thin layers. Some marls form regular rhythmic interlayers with thin clayey and sandy layers.

As an impurity, marls contain organic residues, detrital grains of quartz and other minerals, sulfates, iron oxides, glauconite, etc.

Siderite rocks

The chemical formula of siderite is FeCO 3 , with iron containing 48.2%. The name of the mineral itself comes from the Greek "sideros" - iron.

Siderite rocks are an accumulation of granular or earthy aggregates, dense, sometimes representing spherical nodules (spherosiderite).

Their color is brownish-yellow, brown. Siderite easily decomposes in HCl, while the drop turns yellow due to the formation of FeCl 3 .

Origin.

1. Hydrothermal - occurs in polymetallic deposits as a vein mineral. 2. When replacing limestone, it forms metasomatic deposits. 3. Siderites can also be of sedimentary origin; as a rule, they have an oolitic structure. 4. There is siderite of metamorphic origin, formed during the metamorphism of sedimentary iron deposits. In the oxidation zone, it easily decomposes and passes into iron oxide hydrates, forming iron hats.

Classification of sedimentary clastic (terrigenous) rocks

Lecture topic: Introductory. Geology, content, tasks, sections and methods. A Brief History of the Development of Petroleum Geology.

Abstract of lectures

Geology is the science of the Earth (from the Greek "geo" - Earth, "logos" - knowledge, science). The Earth is a complexly constructed body, occupying a certain position in the Universe, characterized by a certain physical state and chemical composition, and continuously evolving over time. Because of this, besides geology, other sciences are also engaged in the study of the Earth - geophysics, geochemistry. Geophysics studies the internal structure of the Earth, the physical state of its interior, its physical fields - gravitational (gravitational field), magnetic, thermal, electrical. The task of geochemistry includes the study of the chemical composition of the Earth and its individual shells, the fate of atoms of chemical elements and their isotopes. The subject of geology research is mainly the upper stone shell of the Earth - the earth's crust, or rather, the lithosphere, which, in addition to the crust, covers the upper part of the mantle. Geology aims to restore and explain the history of the development of the Earth, based on the study of its material composition, structure and processes that change the internal state of the globe and the earth's surface.

Geology studies the composition, structure and development of the Earth under the influence of processes occurring in its external and internal spheres, as well as the patterns and processes of the formation of the earth's crust, its constituent minerals, rocks, minerals and the history of the development of life on Earth. In general, geological knowledge is a necessary and important link in the scientific worldview.

The significance of geological science for human economic activity has steadily increased as new types of minerals are involved in this activity - from coal to uranium ore and rare elements. Another major task of applied geology is the study of the geological conditions of places intended for the construction of various engineering structures - hydroelectric power plants, nuclear power plants, canals, etc. in order to ensure their sustainability. Another important role of geology is the prevention and consideration of the possible consequences of natural catastrophic events - earthquakes, volcanic eruptions, landslides, etc. Relatively recently, mankind has realized the need to preserve the natural environment and assess the direction of its natural change and ecology - the science of the environment has taken a prominent place among other sciences, and a section related to the geological component of this environment has taken shape in its composition - geoecology.

The practical significance of geology primarily lies in the development of methods for discovering minerals. Among the minerals, there are ore or metal (various metals are mined from them), non-metallic (from which phosphorus, potassium are mined for fertilizers, rock salt, sulfur and others), building materials, precious (diamond, ruby, sapphire and others), semi-precious (amethyst, jasper, malachite and others) stones, combustible (coal, oil, combustible gas).

To date, geology has developed reliable criteria for predicting various minerals, primarily such as oil, natural gas, coal, ores of ferrous and non-ferrous metals. Thus, modern geological science serves as a theoretical basis for prospecting, exploration and development of all types of minerals. Modern industry is largely based on the use of the Earth's mineral resources - oil, gas, coal, ferrous and non-ferrous metal ores, building materials, groundwater, salts, etc. Geology plays a particularly important role in the search for and exploration of deposits of energy and chemical raw materials - oil and gas.

Today, geology is a combination of many geological disciplines that emerged from it as a result of the in-depth development of certain branches of geological knowledge and the improvement of geological research methods. In this regard, several main sections of geology can be distinguished:

1) sciences that study the material composition of the Earth (geochemical cycle); 2) sciences that study the processes occurring in the depths of the Earth and on its surface (dynamic geology); 3) sciences that study the history of the Earth (historical geology); 4) sciences aimed at the practical use of the Earth's interior (applied geology).

The geochemical cycle includes crystallography, mineralogy, petrology, lithology, proper geochemistry. Crystallography - the science of crystals, their external form and internal structure. Mineralogy - the science of minerals, natural chemical compounds that make up rocks or occur separately. Mineralogy considers the chemical composition of minerals, their structural features, physical properties, conditions of occurrence, relationships and origin. Petrology - the science of rocks, studies the mineralogical and chemical composition of rocks, their properties, structure, conditions of occurrence, and also studies their origin and changes experienced by rocks under the influence of various factors. A special class of rocks - sedimentary rocks - is the subject of study lithology (Greek "lithos" - stone). Geochemistry - the science of the chemical composition of the Earth, studies the chemical elements, establishes patterns of distribution, combination and movement of individual chemical elements in the bowels of the Earth and on its surface. Geochemistry operates with atoms, mineralogy studies combinations of atoms (minerals), petrology - combinations of minerals (rocks).

Dynamic geology studies the geological processes occurring in the bowels of the lithosphere and on its surface. Depending on the source of energy, they are divided into exogenous (born from external causes) and endogenous (born from internal causes). Exogenous processes proceed under the action of solar energy in combination with gravitational (gravity); endogenous - under the influence of internal energy, internal heat of the Earth, also in combination with gravitational energy.

Historical geology studies the history of the earth's crust in connection with the development of the earth as a planet as a whole. It, in turn, is subdivided into a number of sciences. Stratigraphy is the study of the layers of sedimentary rocks and the sequence of their occurrence. Paleontology is the science of the fossil remains of organisms. The study of the remains of ancient, extinct organisms buried in the layers, a set of which was characteristic of certain epochs of the Earth's history, helps in establishing the relative age of sedimentary rocks.

The next branch of geology closest to applied geology is regional geology. It deals with the description of the geological structure - the age sequence of rocks, the structural forms they form, as well as the history of the development of individual sections (regions) of the earth's crust, from small to very large - continents and oceans. The structure of the earth's crust is usually depicted on geological maps of various scales, which reflect the distribution of rocks of various types, compositions and ages on the Earth's surface. Geological maps and their derivatives - tectonic and other maps - serve as the basis for prospecting and exploration of minerals.

The main method of geological research is the study of natural outcrops (outcrops) of rocks, starting with a description of their composition, type, conditions of occurrence and relationships. For a more accurate determination of the composition and type of minerals, rocks, minerals, samples (samples) are taken and subjected to laboratory analysis - chemical, mineralogical and others. In sedimentary rocks, searches are being made for organic remains, by which it is possible to determine the relative age of the rock by the paleontological method, and various physical methods for determining the age of rocks are widely used. To study rocks occurring at great depths, data from boreholes, mines and other mine workings are used. Geophysical and geochemical methods are used to study the deep parts of the globe. Geophysical methods are based on the fact that rocks of different composition have different physical properties. Unlike most natural sciences, which make extensive use of laboratory experience in geology, the experimental method is of limited value. The main difficulty lies in the incommensurability of the time scale of geological processes with the duration of human life. However. At present, work is being successfully carried out on the application of the experiment (physical modeling) in various fields of research. So, for example, in tectonics - reproduction of deformation of rocks, mineralogy - synthesis of minerals, including diamond, petrology - melting and synthesis of rocks, in engineering geology and other branches of geological science.

Observations are of primary importance in geological research. In this case, various methods developed on the basis of other sciences are used. The stage of observation and collection of materials is followed by the stage of generalizations and conclusions, which is associated with the establishment of patterns of phenomena and the construction of scientific hypotheses or theories. Further verification of the obtained conclusions is necessary. In geological research, it consists in repeated observation, comparison of a wider range of facts and confirmation by experimental data. One of the most important methods of geological generalizations concerning the nature of geological processes is the method of actualism. The most concise formulation was given by the famous British geologist of the 19th century C. Lyell: "The present is the key to knowing the past." The essence of the method lies in understanding the past by studying modern geological processes and comparing their results with the results of geological processes of the distant past can point the right way to understanding the latter. The successful solution of the theoretical problems of geology is connected with the solution of one of the important practical problems - the forecast of the search for mineral resources necessary for the national economy.

Oil and gas geology studies the origin, conditions of migration and formation of accumulations and the history of these minerals, and also studies oil and gas deposits and deposits in their natural state and in the process of development to determine their significance and rational use of the subsoil.

The purpose of the geological service is to obtain information about the material composition of rocks, their age and structure, the nature of saturation with fluids, as well as the physicochemical properties of oils, gases, groundwater.

Oil, natural gas and their derivatives - combustible minerals - natural formations that can be a source of thermal energy. Combustible minerals serve as the most valuable fuel, and for a substance to be such, it must have a sufficiently high calorific value, be widespread, its combustion products must be volatile so as not to impede the combustion process and not be harmful and poisonous to people.

Fossil fuels are also valuable raw materials for the chemical industry, especially oil.

The oil industry in the world is about 150 years old. Its origin in different countries of the world occurred almost simultaneously.

In 1859, the American entrepreneur Drake (Pennsylvania) received an industrial flow of oil from a well he drilled, which marked the beginning of the US oil industry. Five years later (1864), a retired colonel Novosiltsev in Russia, from a well drilled on the Kudako River (the left tributary of the Kuban River, the northwestern slope of the Caucasus), received a fountain of oil. This fact testifies to the beginning of the oil industry in Russia. In the region of Baku (Azerbaijan), the first industrial oil was obtained in 1871 from a well drilled by the entrepreneur Mirzoev. An oil gusher with a flow rate of 32 t/day blew here from a depth of only 40-45 meters.

The first oil of Kazakhstan was obtained in 1899 in the Karashungul area in well 7 from a depth of only 40 m from Paleogene deposits. The daily flow rate of the well reached 25 tons/day. But, according to many geologists, in fact, the oil industry of Kazakhstan takes its start from Dossor, when on April 29, 1911, well 3 was drilled in the Dossor tract on the salt dome structure of the same name (90 km northeast of Atyrau), from which (interval 225-226 meters, Middle Jurassic) hit a powerful gusher of oil, throwing out over the next few days 16,000 tons of high-quality sweet, oily oil. This date is considered by many oilmen as the actual beginning of the oil industry in Kazakhstan for the following reasons. Karashungul oil migrated to the Paleogene deposits from the underlying Lower Cretaceous and Jurassic deposits, so its reserves turned out to be very modest and it was never used on a large scale. But Dossor oil immediately, in the same 1911, began to be produced in relatively large volumes and intensively used in the economy.

With the birth of the world's oil industry, the geology of oil and gas finally took shape as a separate applied science of the geological cycle. With the development of the oil industry, oil production is growing rapidly. Thus, in Russia in the entire history of the existence of the oil industry (starting from 1864) more than 4 billion tons of oil have been produced.

If the first billion tons took 90 years, then the second took seven, the third only four and a half years, and the fourth less than two years. The depths of oil wells are also growing rapidly from 50-100 meters to 5-7 km at present.

Petroleum geology from the first days of its formation took shape as an independent science of the geological cycle and considers a wide range of issues. It is based on the sciences of geological, chemical, physical and biological cycles.

Oil and gas originate and form accumulations mainly in the rocks of the sedimentary layer. Very rarely, oil and gas accumulate in the granite-gneiss layer of the earth's crust. Consequently, their further conservation and preservation for a long geological time is associated with the earth's crust, the development of which is subject to general geological laws.

Oil, to a lesser extent, and natural hydrocarbon gas are complex chemical compounds, therefore, in order to determine their composition and structure, it is necessary to know and be able to apply the laws of general and organic chemistry (the science of the chemical cycle).

Petroleum science investigates a specific, liquid and gaseous mineral that is able to move (migrate) in the earth's crust. Consequently, when studying the conditions for the formation of accumulations of hydrocarbons (HC) and the patterns of their occurrence, as well as their physical properties, a petroleum geologist uses physical laws (sciences of the physical cycle).

The vast majority of geologists adhere to the organic theory of the formation of oil and gas, therefore biology and biochemistry serve as a support not only in solving the problem of the origin of hydrocarbons, the formation of their accumulations, but also their destruction, including biologically (the science of the biological cycle).

Petroleum geology provides answers to two main groups of questions: how oil and gas were formed and what they are; where to look for these valuable minerals. In other words, petroleum geology provides answers to the following questions: how and where do oil and gas lie in the bowels of the earth's crust, how are their accumulations formed and preserved for millions of years, what are the patterns of their distribution over the globe, how did oil and gas arise in nature in such large volumes.

The main objective of the course is to study the forms of accumulations of oil and gas in the subsoil (types of deposits, fields), the patterns of their location, the conditions for their occurrence, transformation and destruction (generation, accumulation, conservation).

Basic literature: 4, 5,

Further Reading 14

Control questions:

1. What is the date of the beginning of the oil industry in the world.

2. What is the date of the beginning of the oil industry in Kazakhstan

3. On what sciences is petroleum geology based?

4. What questions does the geology of oil and gas study

2. Topic of the lecture: Structure and composition of the Earth. Earth in outer space. The shape and size of the earth. The internal structure of the Earth. Chemical and mineral composition of the Earth's interior. Physical fields of the Earth. The structure and composition of the earth's crust. Material composition of the earth's crust. Minerals. Rocks.

The Earth is one of the countless celestial bodies scattered in the boundless space of the Universe. A general understanding of the position of the Earth in world space and its relationship with other cosmic bodies is also necessary for the course of geology, since many processes occurring on the surface and in the deep interior of the globe are closely related to the influence of the external environment surrounding our planet. The knowledge of the Universe, the study of the state of various bodies and the processes occurring on them shed light on the problems of the origin of the Earth and the early stages of its development. The Universe is the whole world, boundless in time and space and infinitely diverse in the forms that matter takes in its development. The universe consists of countless bodies, very different in structure and size. The following main forms of cosmic bodies are distinguished: stars, planets, interstellar matter. Stars are large active cosmic bodies. The radius of large stars can reach a billion kilometers, and the temperature even on the surface can reach many tens of thousands of degrees. Planets are relatively small cosmic bodies, usually cold and usually satellites of stars. The space between space bodies is filled with interstellar matter (gases, dust). Space bodies are grouped into systems within which they are interconnected by gravitational forces. The simplest system - the Earth with its satellite Moon, forms a system of a higher order - the Solar System. An even more complex structure is characterized by clusters of cosmic bodies of a higher order - galaxies. An example of such a system is the Milky Way galaxy, which includes the solar system. In shape, our galaxy resembles a biconvex lens, and in plan it is a bright cluster of stars in the core with spiraling star streams.

The structure of the solar system. Our solar system includes, in addition to the central luminary - the Sun, nine planets, their satellites, asteroids and comets. The Sun is a star, a hot plasma ball, a typical "yellow dwarf", which is at the middle stage of stellar evolution. The Sun is located within one of the spiral arms of our Galaxy and revolves around the center of the Galaxies with a period of about 200 million years. The temperature inside the Sun reaches several million years. The source of the Sun's energy is the thermonuclear conversion of hydrogen into helium. Spectral study of the Sun made it possible to identify in its composition 70 elements known on Earth. The sun consists of 70% hydrogen, 27% helium, and about 3% of the rest of the elements. The Sun contains 99.886% of the entire mass of the solar system. The sun has a huge influence on the Earth, on earthly life, its geological development. Our planet - the Earth is 149,600,000 km away from the Sun. The planets around the Sun are arranged in the following order: four inner - Mercury, Venus, Earth and Mars (terrestrial planets) and five outer - Jupiter, Saturn, Uranus, Neptune, Pluto. Between Mars and Jupiter is an asteroid belt - several thousand small solid bodies. For geologists, four inner planets are of interest, which are characterized by small size, high density, and low mass. These planets are closest in size, composition and internal structure to our Earth. According to modern ideas, the bodies of the Solar System were formed from the initially cold cosmic solid and gaseous matter by compaction and thickening until the formation of the Sun from the central part. From the particles of the surrounding gas-dust matter, as a result of accretion, planets were formed that revolve in orbits around the Sun.

General characteristics of the Earth. The shape and size of the earth. Under the figure, or the shape of the Earth, we understand the shape of its solid body, formed by the surface of the continents and the bottom of the seas and oceans. Geodetic measurements have shown that the simplified shape of the Earth approaches an ellipsoid of revolution (spheroid). The actual shape of the Earth is more complex, as there are many irregularities on its surface. The closest to the modern figure of the Earth is the figure, in relation to the surface of which the force of gravity is everywhere directed perpendicularly. It is called the geoid, which literally means "earth-like". The surface of the geoid in the seas and oceans corresponds to the surface of the water, and on the continents - to the water level in imaginary channels that cross all the continents and communicate with the World Ocean. The surface of the geoid approaches the surface of the spheroid, deviating from it by about 100 m, on the continents it slightly rises relative to the surface of the spheroid, and in the oceans it decreases. Measurements of the dimensions of the Earth showed the following: equatorial radius - 6378.2 km; polar radius - 6356.8 km; the average radius of the Earth is 6371 km; polar compression - 1/298; surface area - 510 million square kilometers; the volume of the Earth-1, 083 billion. km cube; mass of the Earth-6*10 21 t; average density-5, 52 g/cm 3

Physical properties of the Earth. The earth has certain physical properties. As a result of their study, the general features of the structure of the Earth were revealed and it was possible to establish the presence of minerals in its bowels. The physical properties of the Earth include gravity, density, pressure, magnetic, thermal, elastic, electrical and other properties. Gravity, density, pressure. The force of gravity and centrifugal force are constantly acting on the Earth. The resultant of these forces determines the force of gravity. The force of gravity varies both horizontally, increasing from the equator to the poles, and vertically, decreasing with height. Due to the uneven distribution of matter in the earth's crust, the actual value of gravity deviates from normal. These deviations were called gravity anomalies. They are either positive (in the presence of denser rocks) or negative (in the presence of less dense rocks). Gravity anomalies are studied using gravimeters. The branch of applied geophysics that studies gravity anomalies in order to identify minerals or favorable geological structures in the depths is called gravity exploration. According to gravimetric data, the average density of the Earth is 5.52 g / cm 3. The density of the rocks that make up the earth's crust is from 2.0 to 3.0 g / cm 3. The average density of the earth's crust is 2.8 g / cm 3. The difference between the average density of the Earth and the Earth's crust indicates a denser state of matter in the inner parts of the Earth, reaching about 12.0 g/cm 3 in the core. Simultaneously with the increase in density towards the center of the Earth, the pressure also increases. In the center of the Earth, the pressure reaches 3.5 million atm. Earth magnetism. The earth is a giant magnet with a force field around it. The Earth's magnetic poles are currently located near the geographic poles, but do not coincide with them. Distinguish between magnetic declination and magnetic inclination. Magnetic declination is the angle of deviation of the magnetic needle of the compass from the geographic meridian. Declension can be western and eastern. Magnetic inclination is determined by the angle of the magnetic needle to the horizon. The greatest inclination is observed in the region of the magnetic poles. The influence of rocks containing ferromagnetic minerals (magnetite and some others) is superimposed on the general background of the magnetic field, as a result of which magnetic anomalies appear on the Earth's surface. Magnetic prospecting is engaged in the identification of such anomalies in order to search for iron ores. Studies have shown that rocks containing ferromagnetic minerals have remanent magnetization that preserves the direction of the magnetic field of time and the place of their formation. Paleomagnetic data are used to restore the features of the magnetic field of ancient epochs, as well as to solve problems of geochronology, stratigraphy, and paleogeography. They had a great influence on the development of the theory of lithospheric plate tectonics.

Heat of the Earth. The thermal regime of the Earth is caused by two sources: heat received from the Sun; heat released from the Earth's interior. The Sun is the main source of heat on the Earth's surface. Heating by the Sun extends to an insignificant depth not exceeding 30 m. At a certain depth from the surface there is a belt of constant temperature, equal to the average annual temperature of the area. In the vicinity of Moscow, at a depth of 20 m from the surface, a constant temperature of +4.2 0 is observed. Below the belt of constant temperature, an increase in temperature with depth associated with the heat flow coming from the inner parts of the Earth is established. The increase in temperature in degrees Celsius per unit of depth is called the geothermal gradient, and the depth interval in meters at which the temperature rises by 10 is called the geothermal step. The value of the geothermal step varies widely: in the Caucasus 12 m, in the Emba region 33 m, in the Karaganda basin 62 m, in Kamchatka 2-3 m. It is believed that the geothermal stage persists to a depth of 20 km. Below, the rise in temperature slows down. According to scientists, at a depth of 100 km, the temperature apparently reaches 1300 0 C. At a depth of 400 km - 1700 0 C, 2900 km - 3500 0 C. The sources of the Earth's internal heat are considered to be the radioactive decay of elements, during which a huge amount of heat is released, the energy of gravitational differentiation of matter , as well as residual heat from the formation of the planet.

The structure of the earth. The earth is characterized by a shell structure. The shells of the Earth, or the geosphere, differ in composition, physical properties, state of matter and are divided into external, accessible for direct study, and internal, studied mainly by indirect methods (geological, geophysical, geochemical). The outer spheres of the Earth - the atmosphere, hydrosphere and biosphere are a characteristic feature of the structure of our planet and play an important role in the formation and development of the earth's crust. Atmosphere- the gaseous shell of the Earth, plays one of the main roles in the development of life on Earth and determines the intensity of geological processes on the surface of the planet. The air shell of our planet, the total mass of which is estimated at 5.3 * 10 15 m, is a mixture of various gases: nitrogen (78.09%), oxygen (20.95%), argon (0.93%). In addition, there is carbon dioxide (0.03%), hydrogen, helium, neon and other gases, as well as water vapor (up to 4%), particles of volcanic, aeolian and cosmic dust. Air oxygen provides the processes of oxidation of various substances, as well as the respiration of organisms. There is ozone in the atmosphere at an altitude of 20-30 km. The presence of ozone protects the Earth from the damaging effects of ultraviolet and other radiation from the Sun. Carbon dioxide and water vapor act as a temperature regulator, as it condenses the heat received by the Earth. Carbon dioxide enters the air as a result of the decomposition of organisms and their respiration, as well as during volcanic processes, but is consumed to feed plants. The air masses of the atmosphere are in constant motion under the influence of uneven heating of the Earth's surface in different latitudes, uneven heating of continents and oceans. Air flows carry moisture, solid particles - dust, significantly affect the temperature of various regions of the Earth. The atmosphere is divided into five main layers: troposphere, stratosphere, mesosphere, ionosphere and exosphere. For geology, the most interesting is the troposphere, which is in direct contact with the earth's surface and exerts a significant influence on it. Troposphere characterized by high density, the constant presence of water vapor, carbon dioxide and dust, a gradual decrease in temperature with height and the existence of vertical and horizontal air circulation.

Hydrosphere- a discontinuous shell of the Earth, including the waters of the oceans, seas, lakes and rivers, groundwater and water collected in the form of eternal snow and ice. The main part of the hydrosphere is the World Ocean, which unites all the oceans, marginal and associated inland seas. The amount of oceanic land water is 4 million km 3, continental ice is about 22 million km 3, groundwater is 196 million km 3. The hydrosphere occupies 70.8% of the earth's surface (361 million km 2). The average depth is 3750 m, the maximum depth is confined to the Mariana Trench (11022 m). Ocean and sea waters characterized by a certain chemical composition and salinity. The normal salinity of the waters of the World Ocean is 3.5% (35 g of salts per 1 liter of water). The waters of the ocean contain almost all known chemical elements. It is calculated that the total amount of salts dissolved in the water of the World Ocean is 5*10 16 m. Carbonates, silica are widely extracted from water by marine organisms for the construction of skeletal parts. Therefore, the salt composition of ocean waters differs sharply from the composition of river waters. In ocean waters, chlorides (88.7%) - NaCl, MgCl 2 and sulfates (10.8%) prevail, and in river waters carbonates (60.1%) - CaCO 3 and sulfates (9.9%). In addition to salts, some gases are also dissolved in water - mainly nitrogen, oxygen, carbon dioxide. The waters of the hydrosphere, together with the substances dissolved in it, are actively involved in chemical reactions occurring in the hydrosphere, as well as in interaction with the atmosphere, the earth's crust and the biosphere. The hydrosphere, like the atmosphere, is the active force and medium of exogenous geological processes. The oceans play a huge role in the life of both the entire planet and humanity. In the ocean and in its bowels there are huge reserves of mineral resources, which are increasingly attracted for the needs of mankind (oil, chemical raw materials, etc.). The waters of the oceans are polluted by oil and oil products, radioactive and household waste. This circumstance is acquiring menacing proportions and requires an urgent solution.

Biosphere. The biosphere is the area of ​​distribution of life on Earth. The modern biosphere includes the entire hydrosphere, the upper part of the atmosphere (troposphere). Below the soil layer, living organisms are found in deep cracks, underground waters, sometimes in oil-bearing layers at a depth of thousands of meters. The composition of living organisms includes at least 60 elements, and the main ones are C, O, H, S, P, K, Fe and some others. The living mass of the biosphere in terms of dry matter is about 10 15 tons. The bulk of the living matter is concentrated in green plants capable of accumulating solar energy through photosynthesis. From a chemical point of view, photosynthesis is a redox reaction CO 2 + H 2 O-> CH 2 O + O 2, as a result of which, due to the absorption of carbon dioxide and water, organic matter is synthesized and free oxygen is released. The biosphere plays an important role in the energy of the Earth. Over millions of years, the biosphere has accumulated colossal reserves of energy in the depths - in the thickness of coal, oil, accumulations of combustible gas. Organisms are important rock-forming earth's crust.

Internal structure of the Earth. The study of the deep structure of the Earth is one of the main tasks of modern geology. Only the uppermost (down to depths of 12-15 km) horizons of the earth's crust, which come to the surface or are opened by mines and boreholes, are accessible to direct observation.

Ideas about the structure of the deeper zones of the Earth are based mainly on these complexes of geophysical methods. Of these, the seismic (Greek "seisma" - shaking) method is of particular importance, based on recording the propagation velocity in the Earth's body of waves caused by earthquakes or artificial explosions. In earthquake sources, longitudinal seismic waves arise, which are considered as a reaction of the medium to changes in volume, and transverse waves, which are a reaction of the medium to changes in shape and therefore propagate only in solids. Currently, the available data confirm the spherically - symmetrical structure of the Earth's interior. Back in 1897, E. Wiechert, a professor at the University of Göttingen, suggested the shell structure of the Earth, which consists of an iron core, a stone mantle, and the earth's crust. In 1910, the Yugoslav geophysicist A. Mohorovichic, studying the propagation of seismic waves during an earthquake near the city of Zagreb, established the interface between the crust and the mantle at a depth of 50 km. In the future, this surface was identified at various depths, but they were always clearly traced. She was given the name "Mohorovicic surface", or Moho (M). In 1914, the German geophysicist B. Guttenberg established the boundary between the core and the mantle at a depth of 2900 km. It is called the Wiechert-Guttenberg surface. Danish scientist I. Leman in 1936. substantiated the existence of the inner core of the Earth with a radius of 1250 km. The whole complex of modern geological and geophysical data confirms the idea of ​​a shell structure of the Earth. To correctly understand the main features of this structure, geophysicists build special models. Well-known geophysicist V.N. Zharkov characterizes the model of the Earth: it is “like a section of our planet, which shows how its most important parameters change with depth, such as density, pressure, acceleration of gravity, seismic wave velocities, temperature, electrical conductivity, and others” (Zharkov, 1983, p. 153). The most common is the Bullen-Guttenberg model.

The Earth's crust is the hard upper shell of the Earth. Its thickness varies from 5-12 km under the waters of the oceans, to 30-40 km in flat areas and up to 50-750 km in mountainous areas. The Earth's mantle extends to a depth of 2900 km. It is subdivided into two parts: the upper to a depth of 670 km and the lower to a depth of 2900 km. The seismic method established a layer in the upper mantle in which a decrease in the speed of seismic waves, especially transverse ones, and an increase in electrical conductivity are observed, which indicates a state of matter that differs from the upper and lower layers. The features of this layer, called the asthenosphere (Greek astyanos-weak) are explained by its melting in the range of 1-2 to 10%, which occurs as a result of a faster increase in temperature with depth than an increase in pressure. The asthenospheric layer is located closest to the surface under the oceans, from 10-20 km to 80-200 km, from 80 to 400 km under the continents. The earth's crust and part of the upper mantle above the asthenosphere is called the lithosphere. The lithosphere is cold, so it is rigid and can withstand heavy loads. The lower mantle is characterized by a further increase in the density of matter and a smooth increase in the velocity of seismic waves. The core occupies the central part of the Earth. It consists of an outer core, a transitional shell and an inner core. The outer core consists of a substance in a molten-liquid state. The inner core occupies the core of our planet. Within the inner core, the velocities of longitudinal and transverse waves increase, which indicates the solid state of matter. The inner core consists of an iron-nickel alloy.

Composition and structure of the earth's crust. The most reliable information is available on the chemical composition of the uppermost part of the earth's crust, accessible for direct analysis (down to a depth of 16-20 km). The first figures on the chemical composition of the earth's crust were published in 1889 by the American scientist F. Clark. Subsequently, A.E. Fersman suggested calling the percentage of an element in the earth's crust the clarke of this element. According to A.B. Ronov and A.A. Yaroshevsky (1976), eight elements (in weight%) are the most common in the composition of the earth's crust, making up more than 98% in total: oxygen - 46.50; silicon-25.70; aluminum-7.65; iron-6.24; calcium-5.79; magnesium-3.23; sodium-1.81; potassium-1.34. According to the features of the geological structure, geophysical characteristics and composition, the earth's crust is divided into three main types: continental, oceanic and intermediate. The continental layer consists of a sedimentary layer 20-25 km thick, granite (granite-metamorphic) layer up to 30 km thick and basalt layer up to 40 km thick. The oceanic crust consists of the first sedimentary layer up to 1 km thick, the second basalt layer 1.5-2.0 km thick and the third gabbro-serpentinite layer 5-6 km thick. The substance of the earth's crust consists of minerals and rocks. Rocks are composed of minerals or products of their destruction. Rocks containing useful components and individual minerals, the extraction of which is economically feasible, are called minerals.

Main literature: 1

Control questions:

1 The origin of the solar system.

2 The shape and size of the Earth.

3 Physical fields of the Earth.

4 The internal structure of the Earth.

5 The structure and composition of the earth's crust.

3 Lecture topic: Rocks as a container for oil and gas. A rock is a natural, most often, solid body, consisting of one (limestone, anhydrite) or several minerals (polymictic sandstone, granite). In other words, it is a natural natural association of minerals. All rocks by origin (genesis) are divided into three large classes: igneous, metamorphic and sedimentary.

Igneous rocks were formed as a result of the introduction of magma (silicate melt) into the earth's crust and the solidification of the latter in it (intrusive igneous rocks) or the outpouring of lava (silicate melt) to the bottom of the seas, oceans or the earth's surface (effusive igneous rocks). Both lava and magma are originally silicate melts of the inner spheres of the Earth. Magma, having penetrated into the earth's crust, solidifies in it unchanged, and lava, pouring out onto the surface of the Earth or to the bottom of the seas and oceans, loses the gases dissolved in it, water vapor and some other components. Because of this, intrusive igneous rocks differ sharply in composition, structure, and texture from effusive ones. Granite (an intrusive rock) and basalt (an effusive rock) are examples of the most common igneous rocks.

Metamorphic rocks were formed as a result of a radical transformation (metamorphism) of all other pre-existing rocks under the influence of high temperatures, pressures, and often with the addition or removal of individual chemical elements. Typical representatives of metamorphic rocks are marble (formed from limestone), various shales and gneisses (formed from clayey sedimentary rocks).

Sedimentary rocks were formed due to the destruction of other rocks that previously formed the earth's surface and the precipitation of these mineral substances mainly in an aqueous, less often air environment as a result of the manifestation of exogenous (surface) geological processes. Sedimentary rocks according to the method (conditions) of their formation are divided into three groups: sedimentary clastic (terrigenous), organogenic and chemogenic.

Sedimentary clastic (terrigenous) rocks are composed of fragments of pre-existing minerals and rocks (Table 1). Organogenic rocks consist of the remains (skeletons) of living organisms and their metabolic products (biological way of formation). Chemogenic sedimentary rocks were formed as a result of precipitation of chemical elements or minerals from aqueous solutions (Table 2). Typical representatives of sedimentary clastic rocks are sandstones and siltstones, sedimentary organogenic - various types of organogenic limestones, chalk, coal, oil shale, oil, sedimentary chemogenic - rock salt, gypsum, anhydrite. For a petroleum geologist, sedimentary rocks are dominant, since they not only contain 99.9% of the world's oil and gas reserves, but, according to the organic theory of the origin of oil and gas, are the generators of these hydrocarbons. Sedimentary rocks make up the upper sedimentary layer of the earth's crust, which is not distributed throughout the Earth's area, but only within the so-called plates that are part of the platforms - large stable sections of the earth's crust, intermountain depressions and foothill troughs. The thickness of sedimentary rocks varies widely from a few meters to 22-24 km in the center of the Caspian depression, located in Western Kazakhstan. The sedimentary layer in petroleum geology is usually called the sedimentary cover. Under the sedimentary cover is the lower structural floor, called the foundation. The foundation is composed of igneous and metamorphic rocks. The basement rocks contain only 0.1% of the world's oil and gas reserves. Oil and gas in the earth's crust fills the smallest and smallest pores, cracks, caverns of rock, just as water saturates a sponge. Therefore, for a rock to contain oil, gas, and water, it must be qualitatively different from fluid-free rocks, i.e. it must have pores, cracks or cavities, must be porous. At present, most often industrial accumulations of oil and gas contain sedimentary detrital (terrigenous) rocks, followed by carbonate rocks of organogenic genesis and, finally, chemogenic carbonates (oolitic and fractured limestones and marls). In the earth's crust, porous rocks containing oil and gas must be interbedded with qualitatively different rocks that do not contain fluids, but function as insulators for oil and gas saturated bodies. Tables 1 and 2 show lithofacies of rocks containing oil and gas and serving as seals.

A large group of rocks occurs in various water bodies and in places on
dry land as a result of various chemical processes and the vital activity of animals and plants, as well as due to the accumulation of organic residues after the death of animals and plants. Among them, carbonate rocks, siliceous, sulphate and halide, ferruginous, phosphorite and caustobiolites can be distinguished.

The group of carbonate rocks includes limestone, dolomite and marl.

Limestones(CaCO 3) are most widespread and are formed both by chemical precipitation and mainly by organogenic. Organogenic limestones are usually composed of calcareous shells of mollusks, remains of crinoids, calcareous algae, corals, etc. Depending on the predominance of the remains of certain marine organisms, limestones are called coral, brachiopod, foraminiferal, etc. Among limestones of chemical origin, the following are known: oolitic limestones, which are accumulation of spherical calcareous grains-oolites; calcareous tufas deposited by springs rich in bicarbonate of lime dissolved in water.

writing chalk is a rock formed in two ways. A significant part of it, about 60-70%, is the remains of skeletal formations of planktonic organisms, the rest - fine-grained, powdery calcite - arose chemically.

Marl gives another example of a rock, which has arisen in two ways. It consists of 50-70% CaCO 3 of organic origin, and the remaining 50-30% falls on clay particles, which include particles of both detrital and chemical origin.

Dolomites in terms of chemical composition, they are (by 90-95%) a double carbonate salt of calcium and magnesium CaMg(CO 3) 2 . With a content of at least 50% CaCO 3, the rock is called calcareous dolomite. They can be formed by precipitation from water with high salinity, in which case dolomite layers often alternate with gypsum layers. But more often, dolomites are formed as a result of alteration ("dolomitization") by the corresponding solutions of limestones (or lime sediments before the transformation of the latter into rock) - the so-called exogenous-metasomatic replacement of limestones, as well as by the hydrothermal-metasomatic way (at low temperature).

Siliceous rocks

diatomaceous earth- loose, earthy or weakly cemented yellowish or light gray rock, consisting of an accumulation of skeletal remains composed of hydrous silica (opal) and belonging to microscopic diatoms. They sometimes contain a small admixture of clay particles, grains of quartz and glauconite.

Tripoli similar in properties to diatomite, but differs from it in the absence of remains of obvious organic origin. The rock is composed of the smallest opal grains.

Flask- siliceous light rock, consisting of opal silica (up to 90%) with a small admixture of remains of radiolarians and diatom shells, with grains of quartz, glauconite and clay particles. Most often, the flasks are hard, the fracture is conchoidal, the color is from bluish-gray to almost black.

flint concretions(concretions) are widespread among sedimentary rocks. They are formed in various ways. Some of them arise from the solutions circulating in the rocks by filling the voids in the rocks with the opal-chalcedony substance. Others are formed in the process of diagenesis (regeneration of sediment into rock) by growing around a center from foreign matter as a result of the action of crystallization forces. Concretions with voids inside are called geodes, with a solid core inside - nodules. Siliceous concretions are found in many rocks, but they are especially frequent in limestone strata.

Sulfate and halide rocks, despite the diversity of their chemical composition, are united by the commonality of their origin. Their homeland is drying lagoons and salt lakes separated from sea water bodies. This group of rocks includes such single-mineral rocks as anhydrite (CaSO 4), gypsum (CaSO 4 2H 2 O), rock salt (NaCI).

Iron rocks. The most widespread and of practical importance among them are oolitic brown iron ore, consisting of small, rounded, concentrically shelled or radially radiant formations.

Phosphorite rocks are sedimentary rocks containing 12-40% P 2 O 5 . According to the form of occurrence, phosphorites are distinguished as concretional or nodular, when they are represented by nodules of spherical or irregularly rounded shape, and reservoir, when they are cemented into conglomerate slabs.

Caustobioliths(organogenic combustible rocks). Among them stand out caustobiolites of the coal series, which include peat, brown coal, hard coal, anthracite and caustobiolites of the bitumen series - oil.

Peat consists of semi-decomposed plant remains accumulated over a long period in the specific conditions of swamps and lakes. Decomposition occurred in water with the participation of various microorganisms and with insufficient air flow. The total thickness of peat can sometimes reach several meters. Peat organic matter contains carbon (from 28 to 35%), oxygen (30-38%), hydrogen (5.5%).

brown coals are also the product of changes in plant sediments of previous geological periods. Brown coals are harder and denser than peat: specific gravity is 1.1-1.3. They contain an admixture of clay material, which causes their high ash content. The carbon content in them is in the range of 67-78%. They are a transitional rock from peat to coal.

hard coals represent the next stage in the change of brown coals. They are black, dense, have a greasy or resinous sheen and form a black line on the porcelain plate. Specific gravity - 1.0-1.8; hardness - 0.5-2.5. The carbon content reaches 80-85%.

Anthracite - the last stage of the process of metamorphosis of solid plant remains. The specific gravity of anthracites is 1.3-1.7; hardness - 2.0-2.5; black color; gloss - semi-metallic; line is black. The carbon content is 95-97%.

Oil- natural flammable brown oily liquid. The composition of oil includes C, O, H, of which the main role belongs to carbon and hydrogen. Oil is a mixture of liquid hydrocarbons of methane (C n H 2 n +2), naphthenic (C n H 2 n) and aromatic (C n H 2 n -6) series. The specific gravity of oil is 0.8-0.9. Oil is formed in the thickness of sedimentary rocks accumulating at the bottom of water basins in the presence of dispersed organic matter among silt particles, which is converted into oil with the participation of organic and inorganic catalysts, under conditions of a strictly reducing environment.

Throughout its existence, the Earth has gone through a long series of continuous changes. They are caused by processes different in speed, scale and energy sources. These processes of the movement of matter, modifying the earth's crust and surface of the Earth, are called geological or geodynamic.

endogenous processes called such geological processes, the origin of which is associated with the deep bowels of the Earth. In the bowels of the Earth under its outer shells, complex physical-mechanical and physico-chemical transformations of matter occur, as a result of which powerful forces arise that act on the earth's crust, due to which they transform it. Endogenous processes radically change the nature of the earth's crust and, in particular, its surface; they lead to the creation of the main relief forms of the Earth's surface - mountainous countries and individual hills, huge depressions - receptacles of oceanic and sea water, etc. The main internal sources of the Earth's energy are: gravitational differentiation, rotational (rotational) forces, radioactive decay, chemical and phase transformations occurring in the depths. The processes caused by these energy sources are called endogenous or processes of internal dynamics. These include:

1. tectonic movements (oscillatory and mountain building);

2. magmatism;

3. metamorphism;

4. earthquakes;

The second group of processes is caused by external energy sources and manifests itself on the surface of the Earth and they are called exogenous. These are solar energy and gravity, the movement of water and air masses, the influence of various plant and animal organisms, their impact on rocks and minerals. Such processes are called exogenous or processes of external dynamics. These include:

1. weathering;

2. influence of flowing surface and ground waters;

3. influence of glaciers and water-glacial flows;

4. processes in the frozen zone of the lithosphere;

5. influence of the seas and oceans, lakes and swamps;

6. gravitational processes;

7. human activity (technogenesis).

Endogenous and exogenous processes operate simultaneously and are closely related to each other (Fig. 2.5)

Rocks - a natural collection of minerals of a more or less constant mineralogical composition, forming an independent body in the earth's crust

Rocks are formed during various processes occurring both in the bowels of the Earth and on its surface, forming alloys, mechanical mixtures consisting of one (marble) or several minerals (granite) (Fig. 2.5).

Rice. 2.5. Origin of rocks.

Rocks are classified by origin (by genesis) and chemical composition. Distinguished by origin igneous, sedimentary And metamorphic rocks (Fig. 2.6).

Figure 2.6. Classification of rocks by type of formation

Igneous and metamorphic rocks make up about 90% of the volume of the earth's crust, however, on the surface of the continents, their areas of distribution are relatively small. The remaining 10% are sedimentary rocks, which occupy 75% of the earth's surface area.

Igneous rocks subdivided into intrusive- deep and effusive- poured out.

intrusive rocks are formed in the bowels of the Earth under conditions of high pressures and very slow cooling. Magma at a depth of several tens of kilometers from the Earth's surface is under a very large all-round hydrostatic pressure, reaching several thousand atmospheres, and has a high temperature. When magma intrudes into the overlying layers of the Earth, the physical environment changes: magma meets with solid and relatively cold rocks and begins to solidify and crystallize. However, the release of heat from magma to the environment is very slow, since the thermal conductivity of rocks is low. The temperature of the magma drops gradually over millions of years. The following observation can serve as an example: in the North Caucasus, in the area of ​​Pyatigorsk, magma intrusion occurred at the end of the Paleogene period (~30 million years ago). However, even at present, heated masses of magma exist at a relatively shallow depth, as indicated by hot springs emerging on the surface of the earth.

With the slow cooling of magma, a gradual and successive separate crystallization of its constituent chemical compounds occurs, each of which turns into a crystal of a mineral. Due to slow growth, crystals can reach relatively large sizes, so many intrusive rocks are characterized by a coarse crystalline structure. As a result of the slow cooling of the magma, complete crystallization of all its matter occurs, and no amorphous areas remain in the resulting rock.

The minerals formed during crystallization fall out of the melt in a certain time sequence. This sequence determines the degree of refractoriness of minerals, as well as the chemical composition of magma. An important role in the process of crystallization is played by volatile vaporous and gaseous substances, which contribute to and often determine the order and rate of crystallization of minerals.

Let us explain this by the example of a magma of granitic composition, as a result of which crystallization at a depth a rock is formed - granite. The composition of granite includes such rock-forming minerals as feldspars, quartz, from dark-colored silicates - and less often hornblende (Table 2.4). The melting temperature of biotite and hornblende is very high (at 600 MPa, 620–270 o C), so their crystals form even in liquid magma.

In the second phase of crystallization, feldspar crystals appear, the melting point of which is lower than that of dark silicates (at 10 5 Pa 1120 - 1250 o C). In contrast to the conditions of the first phase, during the crystallization of feldspars, solid crystals of dark-colored silicates already exist in the liquid mass of magma. As a result, feldspar crystals can "overgrow" biotite or hornblende crystals and include them.

After crystallization of dark and light silicates, the rock will be formed by 75-80% of the volume. Silica, contained in excess in granitic magma, will begin to pass into a solid crystalline state last, turning into quartz. Its crystals occupy the free space between the previously formed crystals of biotite, hornblende and feldspar and take the form of grains of irregular shape, although the internal structure of their crystal lattice is quite correct. As a result, complete crystallization of magma will occur, all its substance will take on a crystalline structure. The resulting rock structure is called full-crystalline. The full-crystalline structure provides information about deep, or abyssal, the conditions for solidification of magma.

At great depths under conditions of all-round pressure, the orientation of the axes and planes of growing crystals is not controlled by anything, and their location in the rock is random. A similar texture of the rock is called massive, non-oriented; it is typical mainly for deep rocks.

During magmatic intrusion, a viscous mass of magma may flow, although within limited limits. In this case, crystals with elongated shapes, such as columns of hornblende and mica leaves, are oriented with their long axes parallel to the direction of flows in the magma. The so-called fluid texture. While occurring in intrusive rocks, it is, however, more typical of effusive rocks.

Effusive rocks formed when molten magma erupts onto the earth's surface. During effusion, almost instantly, the ambient temperature and pressure change, decreasing from several thousand atm. up to 1 atm. As a result of this, a rapid release of gases dissolved in magma begins at first, accompanied by explosions. The lava coming out of the vent of the volcano splashes, throwing up spray. The gases released from the lava can froth it, forming numerous bubbles that persist even when the substance solidifies. This creates a bubble texture. A breed of similar build is called pumice. Its density is so low that pumice floats in water.

The sharply decreasing temperature creates conditions under which many minerals crystallize simultaneously. However, the very rapid solidification of the substance leads to the formation of small rudimentary forms of crystals, which can only be detected under a microscope. A significant part of the rock turns into an amorphous or glassy mass. This rock structure is called cryptocrystalline. With a very rapid cooling of the lava, the crystallization process may not begin at all, in which case the rock will entirely consist of volcanic glass. This breed is named obsidian. This is a black, dark gray or dark brown rock with a conchoidal fracture, similar to a block of glass. The cavities of gas bubbles are often filled with minerals, which are formed a second time - as a result of their crystallization from hot water solutions that have penetrated into the solidified lava. At the same time, against the background of a dark gray rock with a cryptocrystalline structure, rounded light spots of such inclusions stand out. Usually they are represented by minerals such as calcite and amorphous silica - opal And chalcedony.

The process of volcanic eruptions is also associated with the formation of a group of rocks, which are commonly called pyroplastic. The gases released from the magma often accumulate inside the vent of the volcano in such large quantities and under such great pressure that powerful explosions occur, throwing huge masses of lava, consisting of particles of various sizes, high into the atmosphere. They cool in the air and fall to the ground in the form of hard dust particles, peas and larger debris. They are called volcanic ash. Masses of this volcanic material cover the surroundings of an erupting volcano with a thick loose layer. Rains wet it, and it sets in motion, forming streams of volcanic mud. Drying, the mud turns into a light porous and hard rock, called tuff. A similar rock formed at the bottom of the sea or lake is called tuffite.

Classification of intrusive And effusive rocks are built on the basis of the above features of the structure and texture, as well as their chemical and mineralogical composition. According to the chemical composition, igneous rocks are divided depending on the content of silicon oxide SiO 2 in them (Table 2.5). Acid rocks are more often light, sometimes white. As the silica content decreases, the color of the rock changes from gray to dark gray. Ultrabasic rocks are characterized by a black or dark green color, depending on the increase in the content of dark-colored minerals rich in iron and magnesium oxides.

Table 2.5. Classification of igneous rocks according to the content of silicon oxide.

Group name		Rocks (examples)
Low and non-silica		pellets
ultrabasic		dunite, peridotite, pyroxenite, kimberlite, olivinite
Main		gabbro, labrodarite, basalt, diabase, trachyte
Medium		syenite, diorite, trachyte, andesite, feldspar, porphyrite
Sour (acidic)		granite, liparite, quartz porphyry
Ultra-acid		pegmatite, alaskite, pumice, volcanic glass

In table. 2.6. a brief description of the main igneous rocks is given.

Table 2.6. Characteristics of the main igneous rocks.

Rock	Mineralogical	Structure
intrusive rocks
Granite red, pink, light gray	Quartz, feldspars (orthoclase, microcline), hornblende, micas
Syenite		Full-crystalline, even-grained and porphyritic
Gabbro	Plagioclases (from labradorite to anorthite), olivine	Full-crystalline, even-grained and porphyritic
effusive rocks
Pumice		Foamy, highly bubbly
Volcanic tuff	From various minerals enriched with silicon	blistered
Volcanic glass (obsidian)	Quartz	glass wool
Liparite (effusive analogue of granite)	Quartz, feldspars (orthoclase, microcline)	Porphyry
Trachyte (effusive analogue of syenite)	Orthoclase, microcline, hornblende, biotite	Porphyritic, fine bubble
Basalt (effusive analogue of gabbro)	Plagioclase, olivine, augite	Dense, finely crystalline, cryptocrystalline
Andesite	Plagioclases, feldspars, hornblende, biotite	Partially crystalline porphyritic, fine-grained

The most widespread in the earth's crust are granites (intrusive rocks), andesites and basalts (effusive rocks).

Granites make up ~30% of the mass of the earth's crust. Granites are composed primarily of three minerals: quartz, feldspar, and mica (or hornblende).

Andesites, rocks interspersed with feldspars (albite, anorthite), hornblende, micas, and pyroxene, make up ~25% of the mass of the Earth's crust.

Basalts make up ~ 20% of the mass of the earth's crust; they mainly include feldspars, pyroxene, and olivine. The rest is accounted for by all other rocks.

Sedimentary rocks are formed during the mechanical and chemical destruction of igneous rocks under the action of water, air and organic matter.

According to their origin, they are divided into three groups: clastic, chemical And organic.

Clastic rocks are formed in the processes of destruction, transfer and deposition of rock fragments. These are most often scree, pebbles, sands, loams, clays and loess. Clastic rocks are divided by size:

coarse clastic (> 2 mm); acute-angled fragments - gruss, crushed stone, cemented by shale, form breccias, and rounded - gravel, pebbles - conglomerates);

medium clastic (from 2 to 0.5 mm) - form sands;

Fine clastic, or silty - form loess;

fine clastic or clayey (< 0,001 мм) – при уплотнении превращаются в глинистые сланцы.

Sedimentary rocks of chemical origin – salts and deposits formed from saturated aqueous solutions. They have a layered structure, consist of halide, sulfate and carbonate minerals. These include rock salt, gypsum, carnallite, flasks, marl, phosphorites, iron-manganese nodules, etc. (Table 2.4). They can be formed in a mixture with detrital and organic deposits.

Marl formed by leaching of calcium carbonate from limestone, contains clay particles, dense, light.

Iron-manganese nodules are formed from colloidal solutions and under the influence of microorganisms and create spherical deposits of iron ores. Phosphorites are formed in the form of cone-shaped concretions of irregular shape, at the confluence of which phosphorite slabs appear - deposits of gray and brownish phosphorite ores.

Rocks of organic origin are widely distributed in nature - these are the remains of animals and plants: corals, limestones, shell rocks, radiolarians, diatoms and various black organic silts, peat, black and brown coals, oil.

The sedimentary layer of the earth's crust is formed under the influence of climate, glaciers, runoff, soil formation, vital activity of organisms, and it is inherent in zoning: zonal bottom silts in the World Ocean and continental deposits on land (glacial and water-glacial in the polar regions, peat in the taiga, salt in the desert, etc.). Sedimentary strata accumulated over many millions of years. During this time, the zoning pattern changed many times due to changes in the position of the Earth's rotation axis and other astronomical reasons. For each specific geological epoch, it is possible to restore the system of zones with the differentiation of sedimentation processes corresponding to it. The structure of the modern sedimentary shell is the result of the overlap of many zonal systems at different times.

In most of the world, soil formation takes place on sedimentary rocks. In the northern part of Asia, Europe and America, vast areas are occupied by rocks deposited by glaciers of the Quaternary period (moraine) and the products of their erosion by melted glacial waters.

Moraine loams and sandy loams. These rocks are characterized by a heterogeneous composition: they are a combination of clay, sand and boulders of various sizes. Sandy loamy soils contain more Si0 2 and less other oxides. The color is mostly red-brown, sometimes pale-yellow or light brown; the build is tight. A more favorable environment for plants is represented by moraine deposits containing boulders of calcareous rocks.

Covering clays and loams - boulderless, fine-earth rocks. Consist predominantly of particles smaller than 0.05 mm in diameter. The color is brownish-yellow, for the most part they have fine porosity. They contain more nutrients than the sands described above.

Loess-like loams and loesses - boulderless, fine earth, carbonate, fawn and yellow-fawn, finely porous rocks. Typical loess is characterized by the predominance of particles with a diameter of 0.05-0.01 mm. There are also varieties with a predominance of particles with a diameter of less than 0.01 mm. The content of calcium carbonate ranges from 10 to 50%. The upper layers of loess-like loams are often freed from calcium carbonate. The non-carbonate part is dominated by quartz, feldspars, and clay minerals.

Red-colored weathering bark. In countries with a tropical and subtropical climate, fine-earth deposits of the Tertiary age are widespread. They are distinguished by a reddish color, highly enriched in aluminum and iron, and depleted in other elements.

Indigenous breeds. In large areas, pre-Quaternary marine and continental rocks, united under the name "bedrocks", come to the surface. These breeds are especially common in the Volga region, as well as in the foothills and mountainous countries. Among the bedrocks, carbonate and marl loams and clays, limestones, and sandy deposits are widespread. It should be noted that many sandy bedrocks are enriched in nutrients. In addition to quartz, these sands contain significant amounts of other minerals: micas, feldspars, some silicates, etc. As a parent rock, they differ sharply from ancient alluvial quartz sands. The composition of the bedrocks is very diverse and insufficiently studied.

metamorphic rocks are igneous and sedimentary rocks altered by temperature, pressure and chemically active substances. Metamorphosis of rocks occurs under the influence of the following factors:

Pressure arising from mountain building processes;

Temperature increase caused by magma penetrating into the lithosphere, hot aqueous solutions and gases carrying new chemically active compounds;

Pressure of overlying rocks.

One of the latest classifications of metamorphism is given in Table. 2.6.

Table 2.6. Classification of metamorphism of rocks

Type of metamorphism	Factors of metamorphism
Immersion metamorphism	Increase in pressure, circulation of aqueous solutions
Heating Metamorphism	temperature rise
Hydration metamorphism	Interaction of rocks with aqueous solutions
Dislocation metamorphism	Tectonic deformations
Impact (shock) metamorphism	The fall of large meteorites, powerful endogenous explosions

For example, during the accumulation of sedimentary rocks with a thickness of 10 - 14 km, their lower layers experience enormous pressure, accompanied by an increase in temperature and recrystallization of the entire material. As a result of this process, first shales are formed from clays, and then gneisses, resembling granite in composition. The composition of gneisses is different. From sands in the presence of iron compounds, first sandstones are formed, which crumble very easily with little effort, and then quartzites, i.e. crystalline rock. Quartzites and gneisses retain the layered structure characteristic of sedimentary rocks. Limestones recrystallize to form marble.

Thus, the processes of metamorphism, as it were, conclude a cycle of changes that occur with rocks.