Sedimentary rocks (SRP) are formed during the mechanical and chemical destruction of igneous rocks under the influence of water, air and organic matter.

Sedimentary rocks are rocks that exist under thermodynamic conditions characteristic of the surface part of the earth's crust, and are formed as a result of redeposition of weathering products and destruction of various rocks, chemical and mechanical precipitation from water, the vital activity of organisms, or all three processes simultaneously.

Under the influence of wind, sun, water and due to temperature changes, igneous rocks are destroyed. Loose fragments of igneous rocks form loose deposits and from them layers of sedimentary rocks of clastic origin are formed. Over time, these rocks become compacted and form relatively hard, dense sedimentary rocks.

More than three quarters of the continental area is covered by geological geological conditions, which is why they are most often dealt with during geological work. In addition, the vast majority of mineral deposits are genetically or spatially related to the UGP. In the UGP, the remains of extinct organisms are well preserved, from which one can trace the history of the development of various parts of the Earth. Sedimentary rocks contain fossils (fossils). By studying them, you can find out what species inhabited the Earth millions of years ago. Fossils (lat. fossilis - fossil) - fossil remains of organisms or traces of their vital activity belonging to previous geological eras.

Rice. Fossils: a) trilobites (marine arthropods found in the Cambrian, Ordovician, Silurian and Devonian periods) and b) fossilized plants.

The starting material for the formation of UCP are minerals, formed by the destruction of pre-existing minerals and rocks of igneous, metamorphic or sedimentary origin and transported as particulate matter or dissolved matter. The science of “Lithology” studies sedimentary rocks.

Various geological factors participate in the formation of sedimentary rocks: destruction and redeposition of destruction products of pre-existing rocks, mechanical and chemical precipitation from water, and the vital activity of organisms. It happens that several factors take part in the formation of a particular breed. However, some rocks can be formed in different ways. Thus, limestones can be of chemical, biogenic or clastic origin.

Examples of sedimentary rocks: gravel, sand, pebbles, clay, limestone, salt, peat, oil shale, hard and brown coal, sandstone, phosphorite, etc.

Rocks are not eternal and they change over time. The diagram shows the process of rock cycling.

Rice. The process of rock cycling.

Based on their origin, sedimentary rocks are divided into three groups: clastic, chemical and organic.

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

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

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

fine-clastic or dusty– form loess;

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

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

Marl is formed when calcium carbonate is washed out of limestone, contains clay particles, is dense and light-colored.

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 nodules of irregular shape, the fusion of which produces phosphorite slabs - deposits of gray and brownish phosphorite ores.

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

The sedimentary thickness of the earth's crust is formed under the influence of climate, glaciers, runoff, soil formation, the vital activity of organisms, and is characterized by zonality: zonal bottom silts in the World Ocean and continental sediments on land (glacial and fluvio-glacial in the polar regions, peat in the taiga, salts in desert, etc.). Sedimentary strata accumulated over many millions of years. During this time, the zonation 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 reconstruct a system of zones with the corresponding differentiation of sedimentation processes. The structure of the modern sedimentary shell is the result of the overlap of many zonal systems of different times.

In most of the territory globe soil formation occurs 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 products of their erosion by melted glacial waters.

Morainic loams and sandy loams. These rocks are distinguished by their heterogeneous composition: they represent a combination of clay, sand and boulders of various sizes. Sandy loam soils contain more Si02 and less other oxides. The color is mostly red-brown, sometimes fawn or light brown; the build is tight. A more favorable environment for plants is moraine deposits containing calcareous boulders.

Cover clays and loams- boulder-free, fine-earth rocks. They consist predominantly of particles less than 0.05 mm in diameter. The color is brownish-yellow, most of them have fine porosity. Contains more nutrients than the sands described above.

Loess-like loams and loess are boulder-free, fine-earth, carbonate, fawn and yellow-fawn, finely porous rocks. Typical loess is characterized by a 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 calcium carbonate content 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 weathered bark. In countries with tropical and subtropical climates, fine-earth sediments of Tertiary age are widespread. They are distinguished by a reddish color, highly enriched in aluminum and iron and depleted in other elements.

Typical example: laterites, a red-colored rock rich in iron and aluminum in hot and humid tropical areas, formed as a result of weathering of rocks.

Rice. Lateritic weathering crusts

Bedrock. In large areas, marine and continental rocks of pre-Quaternary age emerge on the surface, collectively called “bedrock.” The named breeds are especially common in the Volga region, as well as in the foothills and mountainous countries. Among the bedrock, carbonate and marly loams and clays, limestones, and sandy deposits are widespread. It should be noted that many sandy bedrocks are enriched in nutritional elements. In addition to quartz, these sands contain significant quantities of other minerals: micas, feldspars, some silicates, etc. As a parent rock, they differ sharply from ancient alluvial quartz sands. The composition of bedrock is very diverse and insufficiently studied.

Stones of organic origin - selection of stones, photographs, 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 ideas, is a visible trace of the existence of microscopic single-celled plants and animals of the distant past. Even ancient naturalists considered coal to be the brother of oil. Chalk, limestone, marble are waste products of sea creatures...

This is where the list of minerals of biogenic origin that comes to mind for the average person usually ends. However, a knowledgeable mineralogist could go on and on with the list of stones 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. Jewelry Popularity Champion biological nature- pearls!

Mother-of-pearl is the half-brother of pearls

It just didn’t come out in shape. If the 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, were used to make buttons, combs, handles and other consumer goods for many centuries. There is no type of plastic today that would be used as widely and actively as mother of pearl in the recent past.

Palm trees once grew everywhere

...because it was warm and humid. A fossilized palm stem can be found in coal deposits, in clay shales, 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, although a tree-like plant, a herbaceous plant. You can't find annual rings on palm trees! But the longitudinal vessels through which nutritious juices circulated throughout the plant are very clearly visible. It is they - both on the transverse and longitudinal sections of petrified palm wood - that make up all 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 homogeneous siliceous material.

Various silicas, permeating the trunks of flooded, buried, or drowned trees in swamps, often transform unremarkable wood into a precious gem. Silicates, colored by various mineral impurities, acquire a rainbow of colors. Chipping, sawing, or even better, sanding often amazes with the richness of the natural palette of colors.

In this case, the layered wood structure remains, as a rule, clearly visible. Which only adds decorative value to this beautiful stone of biological origin.

Stromatolitic jaspers

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

Red and black are 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 have traces of the first steps of life on the planet been found, made with red jasper on black iron ore...

Fossilized corals

A polished fossil makes you want to blow away specks of dust – nature’s jewelry work is so delicate. The cellular frameworks of marine organisms from the distant past are delicately arranged and skillfully “executed.” The resemblance between fossil coral and the work of a skilled craftsman is endless!

Quartz and calcite, replacing organic tissue in fossilized coral, make jewelry long-lasting. However, fossil polyps do not have the bright colors characteristic of modern corals. Fiery red or transparent yellow earrings made of fossilized corals are a product of artisanal “improvement”.

"Sand Dollar"

The skeleton is called the “Sand Dollar” in both Americas sea ​​urchin, classified as incorrect (this is zoological terminology). Correct hedgehogs– round echinoderms, irregular – flat. They have lived 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.

Irregular hedgehogs have a very conditional needle-like defense, and therefore everyone who is not too lazy feeds on them. However, many of the animals that are as flat as a toy saucer manage to grow a decently thick skeleton, live to their natural death and delight people with the appearance of their skeleton - the “sand dollar”. Dollars “issued” millions of years ago are especially highly valued...

Ammonites

Anyone who has been interested in the history of evolution knows about ammonites. They are sometimes quite modest in size, sometimes two meters in diameter - twisted into a flat spiral, like the horns of the god Amon in one of his earthly incarnations. Ammonites are not difficult to find in natural scree. In some European countries they have long been called “golden snails”.

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

Dinosaur bone

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

Fortunately, dinosaur bones have plenty of time to spare. Over the 65 million years separating us from the last animal lizards on Earth, many tons of bones turned into colored quartz. Moreover, a considerable part of quartz has accepted impurities, which has allowed the hitherto unattractive natural material to acquire the appearance, pattern, and texture of a good jewelry level. Dinosaur bone cabochons are often extremely attractive!

Ivory is younger than dinosaur bones. Today, the name “ivory” includes the tusks of African and Indian elephants, fossil mammoths, walrus tusks, hippopotamus and sperm whale teeth.

The main thing is its luxurious appearance. However, the manufacturability of the material is also important. Not least of all, 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, the warm shades (even red-brown) of a mammoth tusk, and the translucent whiteness of a young elephant’s tusk are prized.

The list of stones of biological origin goes on and on. The gallery of precious gems is replenished with the efforts of geologists, researchers, and pioneers of hard-to-reach areas of the planet.

Like the light of dawn

People found the first pearls while searching for food. Oysters that produce this gem are still loved by gourmets. For thousands of years, people have admired the shine of pearls 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 come in all the colors of the rainbow and even the color of the night! But, as in the old days, this is a stone in which at least half of the mass is organic tissue. We looked at pearls in more detail in the article, and you can see: this stone of biological origin has been in favor with fashionistas for the fifth millennium in a row!

Frozen sunlight...

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

Every amber is a piece of fossilized resin from a tree that grew millions of years ago. There are ambers born in pine groves and ambers obtained from the resin of tropical trees. We talked about amber in the articles: and. Now it’s the turn 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 structure of the massif when fossilized can also give an unexpected visual effect. Particularly interesting are petrified 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 planet’s water bodies. Some of them feed on rotting wood, and in the process of obtaining food they go deep into flooded logs, gnawing through numerous passages.

The subsequent mineralization of organic matter led to an amazing result. The cavities gnawed (more precisely, pierced) by the scale insect were filled with white quartz. The wood fabrics remained colored. Minerologists have dubbed this type of petrified wood “peanut forest” - because the similarity of the stone pattern with sprouting peanuts is almost one hundred percent.

Jet

However, not all plant remains from 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 varieties of stone have a mirror-like gloss and are used to make jewelry. In the recent past, many haberdashery items were made from jet - such as 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 conquered a warm place five hundred million years ago, are still thriving.

The calcareous skeletons of corals number three and a half hundred variations of natural color. Polished corals are an excellent material for making jewelry. However, the user must remember: the deeper the color of the coral, the more organic matter it contains, and the more careful the item must be treated.

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

Pressed carcasses of sea lilies

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

However, crinoid limestone, formed by the remains of flower-like animals three hundred million years ago, under (in literally) Not found in Moscow. Although this mineral is quite widespread.

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

The sonorous name hides a beautiful mineral with an unusual history. Actually, turritella terebra is the name sea ​​mollusk with a helical curled shell. They say that it was Turitella shells that suggested the design of a water-lifting screw to the legendary Archimedes.

Turitella agate is, in fact, a scattering of mollusk shells of a given species in varying degrees of preservation, filled with hardened silicate. Many of the true Turitella agates include sand, water, and air bubbles.

Take a closer look at the appearance gemstone! All kinds of fossilized debris are often sold under the name of agate turitella. If you do not see clearly preserved elements of cone-spiral shells, this is a counterfeit!

Origin and classification of rocks

Any natural stone is “a rock, a natural formation consisting of individual minerals and their associations.” Studying the composition, origin and physical properties Petrography deals with rocks. According to it, all breeds by origin fall into three main groups:
1. Igneous (“primary” rocks)

- formed directly from magma - a molten mass of predominantly silicate composition, as a result of its cooling and solidification. Depending on the solidification conditions, deep and overflowing ones are distinguished.
Deep
arose as a result of the gradual cooling of magma at high pressure inside the earth's crust. Under these conditions, the components of the magma crystallized, resulting in the formation of massive dense rocks with a holocrystalline structure: granite, syenite, labradorite and gabbro.
Poured out
formed as a result of a volcanic eruption of magma, which quickly cooled on the surface at low temperature and pressure. There was not enough time for the formation of crystals, so the rocks of this group have a latent or finely crystalline structure with an abundance of amorphous glass with high porosity: porphyries, basalts, travertine, volcanic tuffs, ash and pumice.

Granite (from Latin granum, grain) - the most common rock. Granite has a distinct granular-crystalline structure and consists mainly of feldspars, quartz, mica and other minerals.

There are 3 different granite structures based on the size of the grains: fine-grained, medium-grained, and coarse-grained. The color of granite can be very different. The most commonly found granite is gray, ranging from light to dark with different shades, but there are also pink, orange, red, bluish-gray and sometimes bluish-green granite. Granite with blue quartz is extremely rare. In decorative terms, the most valuable are fine-grained light gray with a blue tint, deep dark red and greenish-blue varieties of granites.

2. Sedimentary (or “secondary” rocks)

They are called secondary because they were formed as a result of the destruction of igneous rocks or from waste products of plants and animal organisms.
They can be in the form of chemical precipitation that forms during the drying of lakes and bays, when various compounds precipitate. Over time, they turn into limestone tuffs, dolomite. General Feature of these rocks - porosity, fracturing, solubility in water.
There are also clastic sedimentary rocks. These include cemented sandstones, breccias, conglomerates and loose sands, clays, gravels and crushed stones. Cemented deposits were formed from loose deposits as a result of natural bonding and cementation. For example, sandstone is made from quartz sand with lime cement, breccia is made from cemented crushed stone, and conglomerate is made from pebbles.
Rocks of organic origin are also known: limestone and chalk. They are formed as a result of the vital activity of animal organisms and plants.

Sandstone

For geologists and petrographers, a clastic rock consisting of cemented sand. They come in grey, green, red, yellow, brown and brown. Siliceous sandstones are considered the most durable.
Basically, sandstones are not capable of acquiring a polished texture, so they usually use a chipped or sawn texture, and sometimes a polished one. Sandstones lend themselves well to carving and diamond cutting.
Fine-grained red, chocolate brown and green varieties of sandstone, which are successfully used for exterior cladding, are considered decorative. In Moscow and St. Petersburg architectural monuments built in the 19th and early 20th centuries, facings made of Polish sandstone in gray-green, yellow and pink shades are well preserved. Assumption Square of the Kremlin is lined with Lyubertsy sandstone.
Sandstone is a rather porous material, so it is not advisable to use it for finishing elements in contact with water. It is also not recommended to use it on plinth structures.

3. Metamorphic (modified rocks)

- formed by the transformation of igneous and sedimentary rocks into new look stone under the influence of high temperature, pressure and chemical processes.

Among the metamorphic rocks, massive (granular) ones are distinguished, these include marble and quartzite, as well as schistose ones - gneisses and schists.

Marble

The name "marble" comes from the Greek marmaros, shining. This is a granular-crystalline rock that was formed in the bowels of the Earth as a result of the recrystallization of limestone and dolomite under the influence of high temperatures and pressure. In construction, marble is often called not only this stone, but also other dense transitional carbonate rocks. These are, first of all, marble-like or marbleized limestones and dolomites.

Quartzite

These are fine-grained rocks that were formed by the recrystallization of siliceous sandstones and consist mainly of quartz. Quartzite comes in gray, pink, yellow, crimson red, dark cherry and sometimes white.
Quartzite is considered a highly decorative stone, especially raspberry-red and dark cherry. The “rock” texture significantly brightens the overall background of this stone, which is often used when combining such products with polished ones of contrasting color.
Quartzite has a very high hardness and is a difficult-to-cut material, but can be polished to a very high quality.
Often used in the construction of unique structures. It was used in the construction of the Church of the Savior on Spilled Blood. For centuries it was also used as a ritual stone. The sarcophagi of Napoleon and Alexander II were made from it, upper part Lenin's mausoleum.

Slate

Dense and hard rock, which was formed from highly compacted clay, partially recrystallized under high and one-sided pressure (from top to bottom, for example). It is characterized by an oriented arrangement of rock-forming minerals and the ability to split into thin plates. The color of slates is most often dark gray, black, gray-brown, red-brown.
Slate is a durable material, it can be processed (laminated into thin plates), some types can also be polished. However, more often it is used without any processing at all, since the split surface is very decorative.
Slate is used in both external and internal cladding. This stone was widely used in famous architectural monuments(the floors of St. Isaac's Cathedral in St. Petersburg are partly made of slate).

4. Semi-precious stones.

These include mainly rocks called “decorative and ornamental stones”. These are jasper, onyx, opal, malachite, lapis lazuli. They are found much less frequently than ordinary stones and are more valuable. However, it is expensive to cover large areas with them, so most often these stones are used to decorate small elements: parts of columns, window sills, bathrooms...

Onyx (“nail” translated from Greek) is considered one of the most common decorative and ornamental stones. Onyx has a layered or radical-radiant structure. The color of onyx is white, light yellow, yellow, brown, dark brown, pale green. The pattern is striped - alternating stripes of different shades. Most marble onyxes are translucent, sometimes to a depth of 30...40 mm. Onyx can be processed well with cutting and grinding tools and accepts high quality polishing.

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

Endogenous processes These are the geological processes whose origin is associated with the deep interior of the Earth. In the bowels of the Earth, under its outer shells, complex physical-mechanical and physical-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 forms of relief of the Earth's surface - mountainous countries and individual hills, huge depressions - receptacles of oceanic and sea ​​water etc. The main internal sources of energy of the Earth are: gravitational differentiation, rotational (rotational) forces, radioactive decay, chemical and phase transformations occurring in the bowels. 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 called external sources energy and manifests itself on the surface of the Earth and they are called exogenous. This solar energy and gravity, 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 groundwater;

3. influence of glaciers and water-glacial flows;

4. processes in the frozen zone of the lithosphere;

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

6. gravitational processes;

7. human activity (technogenesis).

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

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

Rocks are formed through various processes occurring both in the interior 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 (genesis) and chemical composition. According to origin they are distinguished igneous, sedimentary And metamorphic breeds (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, the areas of their distribution are relatively small. The remaining 10% comes from sedimentary rocks, which occupy 75% of the earth's surface area.

Igneous rocks divided into intrusive– deep and effusive- poured out.

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

With the slow cooling of magma, gradual and consistent separate crystallization of its constituents occurs. chemical compounds, each of which turns into a crystal of a mineral. Due to their slow growth, crystals can reach relatively large sizes Therefore, 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 substance occurs, and no amorphous areas remain in the resulting rock.

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

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

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

At great depths under conditions of uniform pressure, the orientation of the axes and planes of growing crystals is not controlled by anything, and their location in the rock is random. This type of rock texture is called massive, non-oriented; it is characteristic mainly of deep rocks.

During magmatic intrusion, a viscous mass of magma can 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. Occurring in intrusive rocks, it is, however, more typical of effusive rocks.

Effusive rocks are formed when molten magma flows onto the surface of the earth. When effusion occurs almost instantly, the temperature changes environment and pressure decreasing from several thousand atm. up to 1 atm. As a result of this, a rapid release of gases dissolved in the magma begins, accompanied by explosions. The lava coming out of the crater of the volcano splashes, being thrown upward in splashes. Gases released from lava can foam it, forming numerous bubbles that persist even when the substance hardens. This creates a bubbly texture. A breed of this build was named pumice. Its density is so low that pumice floats in water.

The sharply decreasing temperature creates conditions under which many minerals crystallize simultaneously. However, very rapid solidification of the substance leads to the formation of small embryonic forms of crystals that 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. If the lava cools very quickly, the crystallization process may not begin at all, in which case the rock will consist entirely of volcanic glass. This breed is named obsidian. It 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 that are formed secondary - as a result of their crystallization from solutions of hot water that penetrated into solidified lava. At the same time, against the background of dark gray rock, which has a cryptocrystalline structure, rounded light spots of such inclusions stand out. They are usually 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 that are commonly called pyroplastic. Gases released from magma often accumulate inside the crater of a volcano in such large quantities and under such high pressure that powerful explosions occur, throwing huge masses of lava high into the atmosphere, consisting of particles of various sizes. They cool in the air and fall to the ground in the form of solid 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 begins to move, forming streams of volcanic mud. When the mud dries, it turns into a light, porous, hard rock called tuff. A similar rock formed at the bottom of a sea or lake is called tuffite.

Classification of intrusive And effusive rocks are built on the basis of the above-mentioned features of structure and texture, as well as their chemical and mineralogical composition. By chemical composition Igneous rocks are divided depending on the content of silicon oxide SiO 2 (Table 2.5). Acid rocks are often light-colored, sometimes white. As the silica content decreases, the color of the rock changes from gray to dark gray. Ultramafic 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 by silicon oxide content.

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

In table 2.6. given brief description basic igneous rocks.

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, uniform-grained and porphyritic
Gabbro	Plagioclases (labradorite to anorthite), olivine	Full-crystalline, uniform-grained and porphyritic
Extrusive rocks
Pumice		Foamy, highly bubbly
Volcanic tuff	From various minerals enriched with silicon	Bubble
Volcanic glass (obsidian)	Quartz	Glassy
Liparite (effusive analogue of granite)	Quartz, feldspars (orthoclase, microcline)	Porphyritic
Trachyte (effusive analogue of syenite)	Orthoclase, microcline, hornblende, biotite	Porphyritic, finely bubbly
Basalt (effusive analogue of gabbro)	Plagioclases, olivine, augite	Dense, finely crystalline, cryptocrystalline
Andesite	Plagioclases, feldspars, hornblende, biotite	Partially crystalline porphyry, 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 consist mainly of feldspars, pyroxene, and olivine. The rest comes from all other rocks.

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

Based on their origin, they are divided into three groups: clastic, chemical And organic.

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

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

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

· fine-clastic, or dusty – 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 and consist of halide, sulfuric acid and carbonate minerals. These include rock salt, gypsum, carnallite, opoka, marl, phosphorites, iron-manganese nodules, etc. (Table 2.4). They can form in a mixture with clastic and organic sediments.

Marl formed when calcium carbonate is washed out of 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, the fusion of which produces phosphorite slabs - deposits of gray and brownish phosphorite ores.

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

The sedimentary layer of the earth's crust is formed under the influence of climate, glaciers, runoff, soil formation, and the life of organisms, and is characterized by zoning: zonal bottom silts in the World Ocean and continental sediments on land (glacial and aquaglacial in the polar regions, peat in the taiga, salts in the desert, etc.). Sedimentary strata accumulated over many millions of years. During this time, the zonation 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 reconstruct a system of zones with the corresponding differentiation of sedimentation processes. The structure of the modern sedimentary shell is the result of the overlap of many zonal systems of different times.

In most of the world's territory, soil formation occurs 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 products of their erosion by melted glacial waters.

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

Cover clays and loams - boulder-free, fine-earth rocks. They consist predominantly of particles less than 0.05 mm in diameter. The color is brownish-yellow, most of them have fine porosity. Contains more nutrients than the sands described above.

Loess-like loams and loess – boulder-free, fine-earth, carbonate, fawn and yellow-fawn, finely porous rocks. Typical loess is characterized by a 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 calcium carbonate content 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 weathered bark. In countries with tropical and subtropical climates, fine-earth sediments of Tertiary age are widespread. They are distinguished by a reddish color, highly enriched in aluminum and iron and depleted in other elements.

Bedrock. In large areas, marine and continental rocks of pre-Quaternary age emerge on the surface, collectively called “bedrock.” The named breeds are especially common in the Volga region, as well as in the foothills and mountainous countries. Among the bedrock, carbonate and marly loams and clays, limestones, and sandy deposits are widespread. It should be noted that many sandy bedrocks are enriched in nutritional elements. In addition to quartz, these sands contain significant quantities of other minerals: micas, feldspars, some silicates, etc. As a parent rock, they differ sharply from ancient alluvial quartz sands. The composition of bedrock is very diverse and insufficiently studied.

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

Pressure arising during mountain-forming processes;

An increase in temperature 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 rock metamorphism

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 metamorphism	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 all material. As a result of this process, first shales are formed from clays, and then gneisses, reminiscent of granite in composition. The composition of gneisses varies. From sands in the presence of iron compounds, sandstones are first formed, which crumble very easily with the application of little effort, and then quartzites, i.e. crystalline rock. Quartzites and gneisses retain the layered structure characteristic of sedimentary rocks. Limestones, when recrystallized, form marble.

Thus, the processes of metamorphism seem to conclude a cycle of changes occurring in rocks.



Rocks are minerals and their compounds. It is impossible to imagine our planet without the minerals that actually form it.

Classification system

Highlight huge number types of rocks divided into groups. Genetically distinguished:

• sedimentary;
• metamorphic;
• igneous.

The latter are further divided into three classes:

• plutonic;
• hypabyssal;
• volcanic.

Subgroups can be divided into:

• sour;
• average;
• basic;
• ultrabasic.

It is almost impossible to compose full list rocks, considering all the species existing on Earth, there are so many of them. In this article, we will make an attempt to structure information about the most interesting and frequently occurring types.

Metamorphic rocks: list

These are formed under the influence of properties inherent in the earth’s crust. Since transformations occur when substances are in the solid phase, they are visually invisible. During the transition, the structure, texture, and composition of the original rock change. For such changes to occur, you need a successful combination:

• heating;
• pressure;
• influence of gases, solutions.

There is metamorphism:

• regional;
• contact;
• hydrothermal;
• pneumatolyte;
• dynamometamorphism.

Amphibolites

These minerals are also formed by plagioclase. The first is classified as ribbon silicate. Visually, amphibolites are schists or arrays of colors ranging from dark green to black. The color depends on the ratio in which dark-colored components are present in the mineral. Minor minerals of this group:

• pomegranate;
• magnetite;
• titanite;
• zoisite.

Gneisses

In its structure, gneiss is extremely close to granite. It is not always possible to visually distinguish these two minerals from each other, since gneiss copies granite and is close to it in physical parameters. But the price of gneiss is significantly lower.

Gneisses are widely available and therefore are useful in construction. Minerals are diverse and aesthetic. The density is high, so stone can be used as concrete aggregate. With low porosity and low ability to absorb water, gneisses have increased resistance to freezing. Since weathering is also small, the use of the mineral as a facing is allowed.

Slates

When compiling a list of rocks, shales must be mentioned among the metamorphic ones. There are such types of them as:

• clayey;
• crystalline;
• talc;
• chlorite.

Due to the unusual structure and aesthetics of this stone, recent years slate has become an indispensable decorative material used in construction.

Shales are a fairly large group of rocks. List of names of varieties actively used by humanity for various purposes (mainly in construction, repair, reconstruction):

• siltstone;
• golds;
• serpentinite;
• gneiss;
• and phyllite schists.

Quartzite

This stone is known for its durability as it is formed by quartz with added impurities. Quartzite is formed from sandstone when the original elements of the mineral are replaced by quartz during regional metamorphism.

In nature, quartzite occurs in a continuous layer. Frequent impurities:

• hematite;
• granite;
• silicon;
• magnetite;
• mica.

The richest deposits are found in:

• India;
• Russia;
• Canada.

Main features of the mineral:

• resistance to frost, moisture, temperatures;
• strength;
• safety, environmental cleanliness;
• durability;
• resistance to alkalis and acids.

Phyllite

Not the last place in the list of rocks belongs to phyllites. They occupy an intermediate position between clayey and mica shales. The material is dense and fine-grained. At the same time, the stones are obviously crystalline, they are characterized by a pronounced foliation.

Phyllites have a silky shine. Color scheme - black, shades of gray. Minerals are broken into thin slabs. Phyllites include:

• mica;
• sericite

There may be grains, crystals:

• albite;
• andalusite;
• grenade;
• quartz.

Phyllite deposits are rich in France, England and the USA.

Sedimentary rocks: list

Minerals of this group are located mainly on the surface of the planet. To form, the following conditions must be met:

• low temperatures;
• precipitation.

There are three genetic subtypes:

• clastics, which are rough stones formed by the destruction of rock;
• clayey, the origin of which is associated with the transformation of minerals of the “silicate” and “aluminosilicate” groups;
• biochemo-, chemo-, organogenic. These are formed during precipitation processes in the presence of appropriate solutions. Microscopic and not only organisms and substances of organic origin also take an active part in this. The role of waste products is important.

Chemogenic ones include:

• halide;
• sulfate.

List of rocks of this subgroup:

• gypsum;
• anhydrites;
• sylvinite;
• rock salt;
• carnallite.

The most important sedimentary rocks are:

• Dolomite, similar to dense limestone.
• Limestone, consisting of potassium carbonate with an admixture of the same magnesium and a number of inclusions. The parameters of a mineral vary and are determined by the composition and structure, as well as the texture of the mineral. Key Feature- increased compressive strength.
• Sandstone formed by mineral grains bound together by naturally occurring substances. The strength of the stone depends on the impurities and what kind of substance became the binder.

Volcanic rocks

Volcanic rocks must be mentioned. A list of these is created, including minerals formed during the process. In this case, the following are distinguished:

• poured out;
• clastic;
• volcanic.

• andesite;
• basalt;
• diabase;
• liparite;
• trachyte.

Pyroclastic, that is, clastic, includes:

• breccias;
• tuffs.

Almost complete alphabetical list of volcanic rocks:

• anorthosite;
• granite;
• gabbro;
• diorite;
• dunit;
• comatitis;
• patches;
• monzonite;
• obsidian;
• pegmatite;
• peridotite;
• perlite;
• pumice;
• rhyolite;
• syenite;
• tonalite;
• felsite;
• slag.

Organic rocks

Organic rocks are formed from the remains of living beings, the list of which rightfully begins with the most significant substance - chalk. These rocks belong to the group of sedimentary rocks already discussed above, and are important not only from the point of view of their applicability for solving various human problems, but also as rich archaeological material.

The most important subtype of this rock type is chalk. It is widely known and actively used in everyday life: it is used to write on blackboards in schools.

The chalk is formed by calcite, which previously made up the shells of coccolithophorid algae that lived in ancient seas. These were microscopic organisms that inhabited our planet in abundance about a hundred million years ago. At that time, algae could float unhindered across vast areas of the warm sea. As they died, the microscopic organisms fell to the bottom, forming a dense layer. Some areas are rich in deposits of such sediments, hundreds of meters or more in thickness. The most famous chalk hills are:

• Volga region;
• French;
• English.

Studying Cretaceous rocks, scientists find traces in them:

• sea ​​urchins;
• shellfish;
• sponge

As a rule, these inclusions are only a few percent of the total volume of explored chalk, so such components do not affect the parameters of the rock. Having studied the Cretaceous deposits, the geologist receives information about:

• age of the breed;
• thicker than the water that was here before;
• special conditions that previously existed in the study area.

Igneous rocks

Magmatism is usually understood as a set of phenomena caused by magma and its activity. Magma is a silicate melt that is naturally present in liquid form, close to the fire. Magma contains a high percentage of volatile elements. In some cases there are types:

• non-silicate;
• low silicate.

When magma cools and crystallizes, igneous rocks appear. They are also called igneous.

Breeds are distinguished:

• intrusive;
• effective.

The first are formed at great depth, and the second - during an eruption, that is, directly on the surface of the planet.

Often the magma contains a variety of rocks that have melted and mixed with the silicate mass. This is caused by:

• an increase in temperature in the earth's thickness;
• pressurized;
• a combination of factors.

The classic version of igneous rock is granite. Its very name in Latin - “fire”, reflects the fact that the rock in its original state was extremely hot. Granite is highly valued not only for its technical parameters (this material is incredibly durable), but also for its beauty due to its crystalline inclusions.