How are rocks formed?
Minerals are rarely found alone. Their aggregates form rocks, natural natural aggregates of many minerals. So, a very common rock, granite, consists of quartz, feldspar and mica minerals welded together. By their origin, rocks are magmatic, sedimentary and metamorphic .
Igneous and sedimentary rocks are altered by high temperatures and pressures. Loose limestones turn into denser and more durable marble, clays - into shales, granites - into gneisses. Such rocks are called metamorphic (from the Greek metamorphosis - "transformation").
How are igneous rocks formed?
Igneous rocks are formed when magma rises to the Earth's surface. With the slow solidification of magma inside the earth's crust, intrusive rocks (granite, diorite, gabbro) are formed, which have a granular structure due to the large crystals they contain. If magma is poured onto the surface in the form of lava flows, then volcanic, or effusive, rocks are formed. These include basalt, obsidian, consisting of very small crystals - large crystals simply do not have time to grow, since lava cools down relatively quickly.
How are sedimentary rocks formed?
Sedimentary rocks are formed as a result of the accumulation of sediment strata on the earth's surface, the products of destruction of all other rocks. Moving elements - water, wind, glaciers - carry away the debris, and they are deposited in a new place in the form of rubble, pebbles, sand and clay, sometimes at a distance of hundreds and thousands of kilometers from the place of formation. Such sedimentary rocks are called clastic ... Upon evaporation of solutions of mineral substances, chemical sedimentary rocks, which include, for example, table salt, which forms powerful deposits at the bottom of drying salt water bodies.
From accumulations of plant and animal remains are formed organic sedimentary rocks. Their formation took place very intensively in warm shallow seas and lakes rich in life, at the bottom of which, over millions of years, powerful deposits of limestone, chalk, and diatomite had accumulated. On land, over time, from the remains of plants, coals, oil shale, and peat were formed. In organic rocks, fossilized remains of long-extinct animals, clear imprints of parts of ancient plants are often found. Sedimentary rocks are very widespread, they cover 75% of the Earth's surface.
The land is covered with a layer of sedimentary rocks. They consist of particles and debris of other rocks, as well as fossil remains of plants and animals. Rock formation is a continuous process.
It occurs not only deep underground, but also on its surface. Sedimentary rocks are formed by the compaction and cementation of various deposits and the cementation of various deposits (sediments) that accumulate layer by layer.
Classification and types of sedimentary rocks
There are 3 main types of sedimentary rocks: detrital, biogenic (organogenic) and chemogenic.
Detrital sedimentary rocks
Fractured rocks are formed from older rocks, the fragments of which were mechanically transported and deposited in a new place by water, wind, or moving glaciers. These rocks are classified according to the size of their constituent particles - from large fragments to the finest clays. Fragments can be rounded and rounded or broken and angular. They can be unbound (unconsolidated) or cemented material dissolved in groundwater, such as calcite, silica or iron oxides. Clastic rocks make up 75% of all sedimentary rocks.
These shattered layers of marl, a transitional rock from limestone and dolomite to clay, were deposited deep in the sea millions of years ago.
Chemogenic sedimentary rocks
Chemogenic rocks are formed as a result of chemical and physical processes. They can be formed by the precipitation of minerals from seawater, such as flint, a type of silica.
Chemogenic sediments accumulate when water evaporates from salt lakes or shallow seas, such as gypsum and rock salt. It also forms during the leaching process, when groundwater dissolves and redeposits minerals. An example is bauxite, an aluminum ore.
Biogenic sedimentary rocks
Limestone can be formed both by chemical precipitation of calcium carbonate (calcite) and biogenic. Biogenic varieties of limestone, such as chalk, are composed of the skeletons of millions of tiny organisms.
The chalk cliffs in the south of England are fine-grained deposits of soft limestone formed from the skeletons of tiny marine organisms that lived more than 70 million years ago.
Biogenic products that accumulate among sedimentary rocks include various types of fossil fuels. Coal, for example, is compressed plant debris. Oil was formed from organic residues buried under layers of impermeable rocks and exposed to high temperatures, pressure, and bacteria.
Limestone is composed of calcium carbonate and is formed mainly from the skeletons and shells of marine animals. Weakly acidic rainwater partially dissolves limestone. The result is a limestone pavement riddled with holes and cracks, like this one on the coast of England.
Weathering rocks - types of weathering
Weathering is a complex process of destruction of rocks. It can be physical, chemical and organic. Physical weathering is the destruction of rocks under the influence of mechanical effects of wind, water, temperature changes or, for example, as a result of frost wedging, when during the day water penetrates into cracks in the rock, and at night it freezes and expands, breaking the rock.
Chemical weathering refers to the destruction of rocks under the influence of water and dissolved gases or organic acids, leading to a partial change in the chemical composition of rocks. Chemical weathering is accelerated as the temperature rises.
Organic weathering occurs under the influence of the vital activity of plant and animal organisms. For example, tree roots wedge rocks, and decomposition of biomass accelerates chemical weathering.
Conditions for the formation of sedimentary layers
This landscape diagram reflects some of the conditions for the formation of layers of sedimentary rocks.
- Small particles of rock deposited by wind and water in the form of sand.
- Particles of rocks and soil transported downstream by a river stream.
- Delta formed as a result of the deposition of an hour of rocks.
- Continental shelf.
- Continental slope.
- Heavier rocks deposited on the continental shelf.
- Particles of light rocks that have accumulated on the ocean floor are compressed over time and cemented into sedimentary rocks.
- Sedimentary rocks are compressed into metamorphic rocks.
Most of the material that forms sedimentary rocks is transported by rivers. For example, the Mississippi River annually transports 180 million tons of suspended matter to the Gulf of Mexico. In this case, part of the material is deposited on the river bottom, part - at the confluence of the river into the sea, forming a delta, and the main part is carried away into the ocean and accumulates on the ocean floor. Sediment can also be carried by wind and moving glaciers.
During the transfer process, the sediments are sorted by size. Large angular debris is difficult to move, so they can only be found in fast, strong currents. Tiny particles of the clay fraction are transported hundreds of kilometers or deposited in calm waters such as shallow lakes or deep at the bottom of the seas.
Soft clays are formed by particles of destroyed rocks, carried and deposited in a new place by wind, water or glaciers.
Studying the history of the Earth from a cut of sedimentary rocks
More than a billion years of Earth's history is captured in sedimentary layers. In the Grand Canyon in the state of Arizona (USA), a picturesque sequence of sedimentary layers opens up to the eye - a stratum, the depth of which is 1500 m, and the age is about the same million years.
Multicolored layers of sandstone, worn and polished by glacial erosion, form a picturesque striped pattern on gentle hillsides in Arizona, USA. Deflections in the rock are the result of exposure to wind and water.
Sandstone is usually recognized by its brown, pink, or red layers. This variety of colors is due to the presence of varying amounts of iron oxides cementing the sedimentary material.
The red and yellow layers on a cliff wall in Zion National Park, Utah, USA, are Triassic sandstone deposits. Graywacke gray cones were formed as a result of underwater landslides. Multicolored layers of sandstone, worn and polished by glacial erosion, form a picturesque striped pattern on gentle hillsides in Arizona, USA. Deflections in the rock are the result of the impact of water and wind.
The gray sedimentary rock in the foreground - graywacke - dates from the Late Triassic and is about 210 million years old. It is formed mainly by cemented weakly rounded fragments of metamorphic and igneous rocks.
The fossils found in the layers reflect the evolution of life forms from primitive corals and worms to fish, dinosaurs and mammals. The types of sedimentary deposits also tell about the conditions in which they were formed. Rough conglomerates of cemented rounded pebbles suggest that fast rivers once flowed in the area. The sandstone marks the shores of the oceans and river deltas. Clay deposits formed in slow waters, and limestones in warm, shallow seas teeming with life. The relationship between deposits found in different regions of the Earth can be established by comparing fossil remains in rocks and estimating their age using markers such as lava flows.
Origin of rock material
Sedimentary material exists under thermodynamic conditions. It arises in the surface of the earth's crust. UGP occupy almost three quarters of the area of the continents, so people always come across them during geological work. Natural material is formed when various rocks are weathered and destroyed under the influence of liquid, temperature fluctuations and other factors. They are also formed from the waste products of organisms or sediments from the aquatic environment.
OGP appear on the basis of mineral components of destroyed minerals. Most forms of occurrence of natural material are found in the form of layers and layers. Many deposits of stones and other minerals are associated with them. In such formations, the remains of many extinct organisms have been preserved, with the help of which it is possible to learn the history of the development of different parts of the Earth.
In determining the classifications of sedimentary rocks, the peculiarities of the formation of precipitation in physical and mechanical and chemical conditions, which were then led to the appearance of OGPs were taken into account. Most of the work on this issue did the geologist N. M. Strakhov. Based on the properties of the geological materials of lithology studied, it was learned to identify the conditions for the formation of rocks.
There are several OGP groups that are divided by various features. According to genesis (mechanism and conditions of formation), scientists compiled a list of four types of natural materials. In the educational literature you can find tables with the main groups of sedimentary rocks with examples:
- Chemogenic. Form on the basis of salts drop away from aqueous solutions. Examples - anhydrite, bauxite, dolomite, stone salt, Miracycite.
- Cholly. Inorganic rocks such as aneurolite, argillitis, breccia and sandstone are formed as a result of collapsions of fragments of different minerals.
- Organogenic. Appear from the remains of animal or vegetable organisms. Such species include diatomites, stone coal, coral limestone, peat.
- Mixed. Fossils are formed in several ways in several ways and are tufochelitis, tuffs, tuffoffs.
The transitions that occur due to mixed materials of different origin can be observed between the listed OGP groups. With the advent of sedimentary rocks, layeredness and occurring formations in the form of layers are associated.
The composition and structure of OGP are formed under the influence of its genesis. Lithogenesis, which is a combination of geological processes, also determines the properties of sedimentary rocks.
Substances that were formed during the destruction of various rocks are transferred to the wind and deposit, forming sedimentary debris. OGPs are accumulated on the bottom of the reservoirs and the surface of the sushi. Over time, loose accumulations are compacted and acquired a certain structure. All these processes are stages:
- Hypergenez. First, crystalline and other breed are destroyed, and then new solid fossils and solutions are formed.
- Sedimentogenesis. The substances obtained are transferred and deposited on the surface, forming a precipitate.
- Diagenesis. Deposits turn into a new breed.
- Catagenesis. The resulting material happens the first changes.
- Metagenesis. At the end of lithogenesis, the sedimentary breed is converted into metamorphiced deposits.
The last two stages are often combined into one stage - Epiecez. Transformations of sediments pass differently. Environmental factors are also involved in the processes: physico-chemical conditions, pressure, air movement, water flow rate, and so on.
Insofar as Types of OGP differ in the source of origin and the peculiarities of breeding processes They differ in mineral composition in which various chemical elements can be included in the Mendeleev table. Sophisticated unity contains heterogeneous components in the form of relict minerals, claying decomposition products or mica, exogenous neoplasms from true and colloidal solutions.
OGP components are divided into two groups:
- Allogenic. Substances are fragments, volcanogenic material, terrigenous or cosmogenic components. They come from sushi or from the bottom of the reservoirs. Substances are transferred by dragging or as a mechanical suspension, turning into a precipitate. Allotigine components are opposed to hypergenic effects. Examples of mineral components - kaolinitis, quartz, dysten, field swipes, stavolite, zircon. The degree of mechanical processing affects the form of rock, which is spherical, angularly retreed or unicatured.
- Authigenic. These substances appear in sedimentary rocks at various stages of formation. Hydroxides, clay, salts, sulfates, glauconite, chlorites, phosphates, sulfides of certain metals and other compounds are the components of future HCPs. The nature of substances is determined by idiomorphism in pores and cavities, grain structure, spherulite and oolite structure, combination or substitution with other minerals.
According to the stage of formation, authigenic components are also grouped into diagenetic, catagenetic, metagenetic, sedimentation and eluvial. The constituents represent the physicochemical conditions in which the minerals were formed.
Sedimentary rocks are characterized by a varied structure, the features of which depend on the components of the OGP. It is established by the diameter of the grains, but their definition cannot be called unambiguous.
Each type of rock has a specific structure:
- Clastic: coarse clastic, sandy, silty, pelitic, mixed.
- Chemogenic: coarse-crystalline, coarse-crystalline, medium-crystalline, microcrystalline, fine-crystalline, microcrystalline.
- Biogenic: biomorphic, or whole shell (the name is due to the fact that the rocks consist of whole shells or skeletons of organisms), detrius (or bioclastic).
When characterizing the structure of the OPO, one also looks at its porosity. It is inherent in all sedimentary materials, apart from dense chemicals. The pores come in a variety of sizes. In addition, they may contain gas, water or organic matter.
Sedimentary rocks often occur in layers that form when substances accumulate in air and water. Micro-layering is characteristic of sedimentation in rivers and lakes. In the rock, there can be single interlayers that differ in composition and structure from the main OGP. For example, there may be a thin clayey layer in the sand.
The strata occupy a larger area. The layers of excellent compositions differ sharply in them. The strata are bounded on both sides by well-defined surfaces called the roof (top) and bed (bottom). The thickness of the coating is expressed in terms of the distance between the layers. A high rate is observed in marine sediments. A small thickness is characteristic of the continental formations of the Quaternary system. A complex of layers with the same volume, composition and time of origin is called strata.
The formed rocks cover deposits of metamorphic and magmatic origin with a kind of shell. Although sedimentary material makes up only 5% of the earth's crust, it covers a huge surface of the planet, so people build various structures mainly on them.
These breeds have a turbulent history: they saw dinosaurs, survived the Flood and other cataclysms. And today they make people's lives easier and more pleasant.
Sedimentary rocks - destroyed or displaced by the wind, washed away by water fragments of rocks (igneous or metamorphic).
This is the result of several processes:
- Displacement and destruction of other rocks.
- Fallout of chemical elements and compounds from water.
- Concentration of waste products of biological organisms.
The diversity of the "sedimentary" group does not negate the unifying properties of the rocks. This hardness is not higher than average, polymineral composition, structure layering, bedding.
They form on the surface or shallow depths of land, the bottom of reservoirs at low temperature and pressure, precipitating from air or water.
The rocks of this group make up one tenth of the earth's crust, but they have "crawled" to three quarters of the Earth's surface.
They are studied by the science of lithology. Outside of Russia, it is called sedimentology (from the Latin sedimentum - sediment).
Sedimentary rocks of various types have been forming for millions of years. But the stages of the education process are identical.
Sediment on land or on the bottom of a reservoir is an unstable formation from components of different aggregate states (solid particles, gases, liquids).
Under the influence of bioorganisms in its thickness and external natural processes, the transformation process is launched:
- The overlying layers thicken the sediment, which leads to its primary dehydration, dissolution, and removal of unstable components (that is, recrystallization).
- Decomposition of the remains of plants and animals changes the chemical parameters of the sediment.
- The final stage of the stage is the cessation of the vital activity of most bioorganisms, stabilization of the "external environment - sedimentary material" ligament.
Diagenesis takes tens or hundreds of thousands of years, during which a sedimentary layer 12-55 m thick is created, sometimes more.
At this stage, cardinal transformations take place in terms of structure, texture, mineralogical composition.
They are due to the influence of the external environment: temperature, pressure, mineralogical composition of water, radiation.
Sedimentary layers are even more compacted, finally dehydrated, get rid of unstable compounds, bioorganisms.
The result is the formation of new minerals.
The transformation of sedimentary strata at this stage is due to the same, but more pronounced natural factors:
- The degree of mineralization, saturation with gases of water, the temperature is higher.
- Redox (Eh), hydrogen (pH) values change.
The result is the maximum compaction of sedimentary material, a change in the mineral composition, structure, texture. The grains are enlarged, the chaos in the arrangement disappears, the presence of fauna remains is nullified.
Finally, sedimentary rocks move to the metamorphic group.
Method of education
According to the method of formation, the following classes of rocks are distinguished:
- Mechanogenic. Samples of mechanical destruction that retained the properties of minerals. They are also known as terrigenous and detrital rocks - according to the source of the initial material, the mechanism of formation, transfer, and composition. They can form at the bottom of water bodies.
- Chemogenic. Formed by precipitation of minerals from water, other solutions.
- Organogenic. They are created similarly to chemogenic, but from organic components.
- Mixed. Transitional specimens created by mixing materials of sedimentary and other origin. In fact, an intermediate link between volcanic and sedimentary rocks.
Hundreds of millions of years old, natural cataclysms plus the conditions of formation have caused diffuseness, transitional stages between groups of sedimentary rocks.
Sedimentary rocks are called secondary.
The division of rocks of sedimentary origin into groups in accordance with the physicochemical characteristics has been developed.
They consist of fragments of minerals, remains of biological organisms (calcareous trunks, tree branches, animal skeletons).
This group is made up of silts, pebbles, sands and their fragments.
Fragments are cemented by clay matter of different composition: ferruginous, siliceous, carbonate. But the density is still low - a maximum of 2 g / cm3.
The dimensions of the fragments are from 0.01 to 10+ mm. They have different shapes (almost always smooth, but not necessarily round).
They often appear in the literature as volcanogenic-sedimentary or pyroclastic.
Generated by volcanism, they are found near volcanoes - active or dormant for hundreds of years. Moreover, on land or under water.
In fact, it is a mixture of products of volcanic eruptions: ash, pumice, sand, slag.
Dispersed products are the result of chemical transformation of aluminosilicate and silicate components of parent rocks.
The group unites more than fifty items with different mineral, chemical and organic composition.
The general characteristic of clayey rocks is the dominance of particles of microscopic dimensions (0.01-0.001 mm).
Two types have been identified - clays proper and mudstones.
Biochemogenic and organogenic rocks are created as a result of sedimentation from solutions or concentration of organic substances. Different organisms or products of their vital activity are involved in the process.
These are oil, coal, peat.
The nomenclature of minerals of sedimentary origin has hundreds of names.
- Dolomite. The material of cryptocrystalline structure is appreciated (according to the description it resembles porcelain).
- Gypsum. The varieties of alabaster and fibrous (selenite) - white or yellowish-pink in color with a silky sheen - are especially in demand.
- Sandstone. Varieties: gypsum, glauconite, clay, ferruginous, calcareous, quartz, siliceous, micaceous. Determined by the dominant material.
- Argillite. Dense dark gray clay.
- Halite. Rock salt.
- Limestone. Varieties: shell rock, coral (from coral polyps), chalk, calcite, tuff.
- Marl. A collection of gray or brown sedimentary rocks from clay, dolomite and limestone.
- Diatomite. The base is opal. Plus clay minerals, quartz, remnants of marine organisms (shells of diatoms, sponges, radiolarians).
- Trepel. Looks like diatomite. It is possible to distinguish only on special equipment.
- Peat. Material from non-decayed plant fragments.
- Coal. Varieties: brown, stone, anthracite. The latter is the most energetically beneficial.
- Oil. Consists of carbon, hydrogen, oxygen compounds, sulfur, nitrogen. Plus organic and inorganic impurities.
- Asphalt. Dense mountain resin with the dominance of hydrogen and carbon in the composition.
- Ozokerite (mountain wax). It turns out when light components volatilize from oil saturated with paraffins. Looks like beeswax, but darker. Combustible.
Sedimentary rocks include opal and amber.
Opals are petrified trees and skeletons of small animals, amber is the hardened resin of coniferous trees 26-31 million years old.
Where are used
Sedimentary raw materials are ubiquitous:
- Houses and other buildings are erected from it.
- Highways, railroad tracks, garden paths are laid with them.
- Coal, oil, peat, gas are used as a source of heat and light.
- These are dozens of types of products of the chemical, metallurgical, glass industries.
- Ozokerite is used to treat or heal the body.
- Food is not tasty without salt.
Raw materials of sedimentary origin are inexpensive, only decorative materials are at a high price. For example, a type of calcareous tuff travertine. It is used as a covering for walls, fireplaces, countertops material, and other similar products. Amber and opal are taken by jewelers, collectors of mineralogical collections.
Sedimentary rocks are mined all over the planet in millions of tons, mining is carried out in an open-pit or mine way.
Significance for science
The age of sedimentary rocks is 55 - 280 million years. In addition to their practical application, they are an ally of scientists.
The remains of well-preserved extinct organisms are found in the sedimentary layers. They are used to reconstruct the geological, biological, climatic history of the planet for hundreds of millions of years.
For example, brown coal is studied by paleobotanists. The boulders retain imprints of flora that grew on Earth from the era of the dinosaurs or earlier.
Lithology is the science that studies sedimentary rocks. Scientists around the world study and collect information about fossils, study their features and conditions of formation. They also review and evaluate the structure, origin, composition and other characteristics of the mined materials.
What are sedimentary rocks
Sedimentary rocks (SSS) are a category of fossils formed as a result of their subsidence at the bottom of water bodies and on continental zones under various circumstances. It can be a precipitate from the water, the result of the vital activity of flora and fauna. Of the earth destroyed rocks. Sedimentary rocks cover more than 70% of the continental surface of the planet. Their mass is equal to a tenth of the total mass of the earth's crust. Geological research is carried out mainly in the continental zones. Almost all minerals planets, one way or another, are associated with sedimentary rocks.
Classification of sedimentary rocks
All sedimentary rocks differ in their various compositions, different kinds of conditions under which they were formed, properties and characteristics. There are breeds that consist of only one component. There are also multicomponent OCPs. There is far from one general classification of them, which would be suitable for both scientists and researchers. This happened due to the huge variety of rocks, so all groups of planetary researchers use different classifications.
OCP are classified according to their composition:
Also, breeds are classified into groups:
Oxide rocks include water, siliceous, manganese, ferruginous rocks, and bauxite. Carbonate and phosphate sedimentary rocks are a salt group. The organic group of rocks includes oil, solid combustible substances, anthraxolites. The composition of silicate rocks includes clays, detrital quartz-silicate rocks.
From the name it can be understood that these rocks are composed of various debris formed as a result of the physical fracture of natural materials. They move through the territory under the influence of the gravity of the Earth using water , wind or ice, after which they are deposited.
Clastic rocks are usually understood as gravelstones, siltstones, sandstones, the fragments of which are represented by various minerals. They are usually cemented by a substance that has a clay or carbonate composition. Also clastic are sedimentary rocks that were initially destroyed into fragments, and then cemented.
These breeds can be like loose and non-relaxed (crushed stone, collar, gravel, pebbles), and crafted and compacted (Dressman, Bracia Glubovaya).
These are rock rocks that consist of volcanic rocks at least 50%. They are formed during eruptions from lava, volcanic sand, dust. Impurities other breeds in no way related to activities volcanoes The composition must be less than half.
By origin, volcanogenic-chip rocks are divided into exposive-chip and effusive-chip. The first were formed due to the eruptions of the explosive type, as a result of which the accumulation of loose material appeared. Next, this material was bonded with each other by cement. Effusion-chip breeds were formed due to the process of crushing lava during its cooling.
Volcano-chip rocks are customary to use for the manufacture of a variety of building materials. It is cement, glass, and materials used for thermal insulation.
These are the most frequent sedimentary breeds. They occupy more than half the volume of all breeds on earthly crust. These are mainly consisting of small particles, but are formed as a result of the weathelation of magmatic rocks.
Clay breeds are distributed on clay and argillitis .
Clay Spirling well in the aquatic environment, quickly absorb moisture, becoming soft and plastic. The color of these breeds is diverse and depends on which minerals are part. Clay are divided into kaolins, bentonites, hydropower clays. Kaolins have a fatty texture, do not swell in the aquatic environment. Used as raw materials in the production of porcelain and faience. Bentonites falling into Water medium , swell, acquiring plasticity. Hydropoid clays in water do not increase. These breeds are used to produce ceramic products and refractory bricks.
Argillitis - These are clay with high density that do not spin in the aquatic environment. They include quartz, mica, twin. In the color range of argillitis is more dark than clay.
Biochemical sedimentary rocks are formed as a result of chemical reactions in which microorganisms and rocks with chemical and organogenic origin are involved. They are multist, siliceous, carbonate and phosphate.
Medist sandstones and shale rocks that contain copper minerals are copper ore. The layers of sandstones occupy a large area and are represented by such minerals as boring, chalcopyrite, as well as iron sulphides, zinc, lead, cobalt.
Silicon biochemical rocks have different mineral composition. They are divided into diatomites, geysers, trees, radiologists, leeddits. They differ in the porosity of the structure, the volume of impurities of clay substances, have different color.
Carbonate rocks were formed from shells, skeletons of marine and freshwater inhabitants, plants and bacteria, which over time accumulated on the bottom of the reservoirs. They gradually compacted and changed the structure.
Phosphate rocks are highly enriched with calcium phosphates. They have a layered grain structure. Under the conditions of formation and location, phosphate sedimentary rocks are divided into several types of phosphorites: grainy, afanite, crocheted, reservoir and concrete. Phosphates accumulate at the bottom of the reservoirs from different components of the living matter: DNA molecules, RNA, tissues and cells.
Formation of sedimentary rocks
The formation of sedimentary rocks is slow and gradual. It occurs on the surface, in water bodies and the near-surface part of the Earth and has several stages:
- Sludge formation.
- Transfer of sedimentary material.
- Accumulation of it in a certain place.
- Conversion of sedimentary material into rock (diagenesis).
- Consolidation of materials (catagenesis).
- Deep transformation and maximum compaction of the rock (metagenesis).
Sediment that has formed at the bottom of a water body or on the surface of the Earth consists of different layers ... These layers, in turn, can consist of solid, liquid or gas materials. Over time, an interaction begins between the phases, in which living microorganisms participate. The layers are being converted.
During diagenesis, all phases of the sediment are compacted, excess moisture and unstable components are removed and mineral rocks begin to form. This stage lasts for many decades and functions in the range of several tens of meters.
Sedimentary rocks undergo significant changes due to temperature, pressure and water masses. The chemical and mineral composition, structure, properties change. The rocks are compacted even more, changing their structure, forming new minerals. Unstable compounds disappear and recrystallization occurs.
The process of metagenesis is similar to catagenesis, but here a high temperature acts on the compaction of rocks, reaching 200-300 ° C in some areas. Sedimentary rocks are compacted as much as possible under such conditions. At this stage, the remnants of the fauna are transformed, as a result of which the rocks are transformed into metamorphic rock formations.
Age of sedimentary rocks
Their age can be determined relatively. It is believed that the rocks to which there is access for further study are 3.8 billion years old. The layers that are in the deepest places are considered the most ancient. The phases lying closer to the surface are of a younger age.
The development of organic life on Earth was gradual. The remains of the simplest organisms are found in the oldest rocks. The skeletons of more advanced organisms are enclosed in younger rocks. Thus, all layers of sedimentary rocks have a different structure, age, and formation conditions.
Sedimentary rock properties
Basic sedimentary rocks include limestone, sandstone and dolomite.
Limestone has many varieties, it consists of calcium, magnesium, argillaceous or ferruginous impurities. These rocks are diverse in composition, texture, strength. Limestone is often used in construction, but at the same time it is treated with water-repellent compounds. It tends to dissolve in water, albeit very slowly. Has unobtrusive pastel colors.
Sandstone is formed from grains of minerals that have been cemented by various substances. Has high strength and fire resistance. It is used in construction for decoration of buildings, as well as in the production of decorations. The properties of the stone depend, as a rule, on the deposit and the composition of the fragments.
Dolomite is a rock containing at least 95% of the dolomite mineral. It is of medium hardness, varied in color: white, yellow, gray or black with a greenish tint. It is used in the metallurgical industry and has high refractoriness.
Mineral resources of sedimentary rocks
Mineral resources are all sorts of minerals and rocks used by man for the production of materials, for the conduct of the national economy. According to their physical state, there are solid, liquid or gas fossils. Hard rocks include coal, marble, granite, salt and ores. Liquid water is mineral water and oil. Methane and combustible gases are gas fossils.
According to the methods of application, they are divided into combustible, ore and non-metallic minerals. The group of combustible rocks includes coal, oil, peat and gas. Ore - a variety of rock ores. Non-metallic minerals include sand, clay, limestone, and salts.
Valuable semi-precious stones and precious materials are not included in any of the listed groups, but stand in a separate category.
Sedimentary rock structures
The structure is understood as a variety of features of rocks: the size and shape of particles, their interaction with each other, the degree of crystallization, the conditions of formation. There is such a classification of structures:
The psephite structure has a particle size of more than 1mm. Fractions with this size are considered the largest. Psammitic structure - the size of fragments is from 1 mm to 0.1 mm. Silty - particle size in the range of 0.1 - 0.01 mm. As a rule, clayey rocks have a pelitic structure, and the particle size in them reaches less than 0.01 mm.
Organic and inorganic sedimentary rocks
Organic rocks were formed as a result of the functioning of living organisms. They are divided into phytogenic, formed as a result of the vital activity of plants, and zoogenic, formed as a result of the vital activity of representatives of the animal world. From the remains of plants, coals and some types of oil arose, and from animals - limestones.
Inorganic rocks were created by weathering. Also, their formation was influenced by temperature fluctuations, the strength and speed of the wind, the fluidity of water in reservoirs. Rock salt, gypsum, gravel, sand, pebbles are examples of inorganic rocks.
Examples of sedimentary rocks
- - clay;
- - limestone;
- - coal;
- - brown coal;
- - sandstone;
- - breccia;
- - siltstone;
- - bauxite;
- - peat;
- - slate;
- - rock salt;
- - dolomite;
- - diatomite;
- - laterite;
- - plaster.
The simplest sedimentary rocks
Kieselguhr or mountain flour is a mineral that was formed from the simplest marine organisms. These were diatoms that already lived on Earth millions of years ago. Mountain flour formed from their valves.
Diatoms seaweed look very unusual, as they have a silicon shell. Due to this, mountain flour is saturated with calcium, silicon and many other minerals. These minerals are usually loose, gray or yellowish in color. In diatomite, you can find particles of opal, detrital and clayey rocks.
The importance of sedimentary rocks in nature
Sedimentary rocks are of great importance in nature: they consist of 5% lithosphere , they cover more than 70% of the continental surface of the planet. Rocks are used as minerals, and also serve as the basis for the construction of structures.
Human use of sedimentary rocks
People extract minerals in mines and quarries, and then use the objects produced from them in everyday life. In nature, rocks are in a solid, liquid or crumbly state.
From sedimentary rocks, people use salt for cooking, graphite for making pencils, coal and gas for heating rooms, marble and limestone for building, clay for making porcelain, gold and precious stones for jewelry. The amount of sedimentary rocks in metallurgy is over 50%. The reserves of energy raw materials in all countries are different, since the resources are unevenly located.