Coal: brown, hard, charcoal, their types and uses. Where does so much oil, gas and coal come from on earth? (1 photo) How coal is made

This question may seem naive at first. Every diligent schoolchild will say without hesitation: coal is a substance of plant origin, “a product of the transformation of higher and lower plants” (Soviet encyclopedic dictionary all publications). Not a single textbook or popular book calls this truth into question. At school we were firmly convinced of the chain: “plants - peat - brown coal - hard coal - anthracite”... Well, let's take a closer look at the textbook theory of coal formation.

So, in some stagnant reservoir it rots organic matter. Peat is gradually formed from the plant mass. As it sinks deeper and deeper, covered with sediment, it becomes denser and, as a result of complex chemical processes, becomes saturated with carbon and turns into coal. Peat practically does not react to a small load of sediment, but under powerful pressure, dehydrating and compacting, its volume can decrease many times over - something similar happens when pressing peat briquettes.

Nothing new, that’s exactly what they write everywhere. However, now let us pay attention to the following circumstance. The peat deposit is surrounded by sedimentary rocks that experience the same vertical loads as the peat. Only the degree of their compaction cannot be compared with the degree of compaction of peat: sands almost do not shrink in volume, and clays can lose only up to 20-30% of their original volume or a little more. Therefore, it is clear that the roof over the peat deposit, as it compacts and turns into coal, will sag and a collapsed chest fold will form above the layer of “newly minted” coal.

The dimensions of such folds should be very significant: if a ten-centimeter layer of coal is obtained from a meter-long layer of peat, then the amplitude of the fold deflection will be about 90 cm. Equally simple calculations show: for coal seams and layers of any thickness and composition, the dimensions of the expected folds are so large that it is impossible to it would be impossible to notice them - the amplitude of the failure will always exceed the thickness of the formation itself. However, here’s the problem: we have neither seen such folds nor read about them in any scientific publication, both domestic and foreign. The roof over the coals lies calmly everywhere.

This means only one thing: the parent material of the coals either did not decrease in volume at all, or decreased as little as the surrounding rocks. And therefore, this substance could not possibly be peat. By the way, the reverse course of analysis leads to exactly the same conclusion. If, with the help of a pencil and paper, you try to restore the original position of the cuts at the moment when the peat had not yet turned into coal, you can be convinced that such a problem has no solution, it is impossible to construct a cut. Anyone can be convinced: layers of the same age will have to be torn apart and placed at different heights - in this case there will not be enough layers, awkward bends and voids will appear, which in fact do not exist and cannot exist.

No single remark or study, even a very reasonable one, can cancel the established scientific views, especially if they are more than one hundred years old. Therefore, let's talk a little more about peat shrinkage. It is estimated that during the formation of brown coal, the coefficient of this shrinkage is on average 5-10, sometimes 20, and during the formation of hard coals and anthracites - even more. Since a vertical load acts on the peat, the layer seems to be flattened. We have already said that a meter-thick layer of peat can produce a layer of brown coal one decimeter thick. So what happens: the unique Hat Creek coal seam in Canada, about 450 m thick, gave rise to a peat layer 2 - 4 km thick?

Of course, no one is forbidden to assume that in ancient times, when many things on Earth were believed to be “bigger,” peat bogs could reach such cyclopean sizes, but there is absolutely no evidence in favor of this. The thickness of peat layers in practice is measured in meters, but never in tens, let alone hundreds. Academician D.V. Nalivkin called this paradox mysterious.

The most large number fossil coals formed at the end Paleozoic era, in the so-called Permian period 235 - 285 million years ago. For those who believe textbooks, this is strange, and here's why. In the luxurious Czechoslovak gift albums of Augusta and Burian, you can see colorful pictures depicting the dense, impenetrable horsetail-fern forests that covered our planet in the Carboniferous era preceding the Permian. There is even a term: “coal forest”. However, until now no one has really answered the question of why this forest, despite its name, did not produce as much coal as the arid and plant-poor Permian.

Let's try to dispel one surprise with another. During the same Permian period, the most generous with coals, in the same coal regions, deposits of stone and potassium salts. Where there is a lot of salt, nothing grows or grows with great difficulty (remember salt marshes - a type of desert). Therefore, coal and salt are considered to be antipodes, antagonists. Where there is coal, there is nothing to do with salt, they never look for it there - but... every now and then they find it! Many large coal deposits are in the Donbass, the Dnieper basin, in eastern Germany— literally sitting on salt domes. In the Permian time (and no one disputes this), the most powerful accumulation of rock salts in the geological history of the Earth occurred. The following scheme has been adopted: the drying heat, the water of the lagoons and bays evaporates, and salts precipitate from the brines, similar to what happens on Kara-Bogaz-Gol. Where can we find botanical splendor here? But the coals came nevertheless!

It is still unclear how and under what conditions peat can turn into coal. It is usually said that peat, slowly sinking into the depths of the Earth, successively falls into areas of increasing temperatures and pressures, where it is converted into coal: at relatively low temperatures- brown, at higher levels - stone and anthracite. However, experiments in autoclaves were unsuccessful: peat was heated to various temperatures, different pressures were created, and kept under these conditions for as long as desired, but no coal, not even brown, was obtained.

In this regard, different assumptions are made: the range of expected temperatures for the formation of brown coal varies, supposedly, with different durations of the process, from 20 to 300 °C, and for anthracite from 190 to 600 °C. However, it is known that when peat and its host rocks were heated to 300 °C and higher, it would ultimately turn not into coal, but into completely special rocks - hornfels, which in reality does not exist, and all fossil coals are a mixture of substances not wearing no traces of exposure to high temperatures. In addition, based on some quite trivial signs, it can be confidently stated that the coals of many deposits have never been located at great depths. As for the duration of the coal-forming process, it is known that the coals of the Moscow region, one of the oldest in the world, still remain brown, and among many young deposits there are anthracites.

Another reason for doubt. Peat swamps, the ancestors of future coal basins, would have to arise on vast plains located away from the mountains, so that slow-moving rivers could not bring rock fragments (called terrigenous material) here. Otherwise, the peat will be silted and clean coal will never be produced from it. In this case, a strictly stable tectonic regime is also required: the bottom of the swamps must sink slowly and smoothly enough so that the vacated volume has time to fill with organic matter.

However, the study of coal-bearing regions shows that coal deposits often arose in intermountain depressions and foothill troughs, near the front of growing mountains, in narrow slot-like valleys - in a word, in places where terrigenous material accumulates very intensively, and where peat bogs, therefore, can be not only silted up, but also completely destroyed by stormy mountain streams. It is in such unsuitable (according to theory) conditions that thick coal seams are found, reaching 50-80 m.

It takes a long time for peat to turn into coal. Peat gradually accumulates in the swamp. The swamp, in turn, is overgrown with ever larger layers of plants. At depth, the peat changes all the time. Complex chemical compounds, which are found in plants, break down into simpler ones. They partially dissolve and are carried away with water, and partially transform into a gaseous state: carbon dioxide and methane. Important role During the formation of coal, bacteria and all kinds of fungi that inhabit everything play a role. They promote the decomposition of plant tissue. In the process of such changes in peat, the most persistent substance, carbon, begins to accumulate in it over time. Over time, the carbon in the peat becomes more and more.

The accumulation of carbon in peat occurs without access to oxygen, otherwise carbon, combining with oxygen, would turn completely into carbon dioxide and evaporate. The forming layers of peat are first isolated from the oxygen of the air by the water covering them, then by the newly emerging layers of peat.

This is how the process of turning peat into peat gradually takes place. There are several main types of fossil coal: lignite, brown coal, hard coal, anthracite, boghead, etc.

Most similar to peat lignite- loose coal of brown color, not very ancient origin. The remains of plants, mainly wood, are clearly visible in it (hence the name “lignite”, which means “wooden”). Lignite is woody peat. In modern peat bogs of the temperate zone, peat is formed mainly from peat moss, sedge, and reeds, but in the subtropical zone of the globe, for example, in the forest swamps of Florida in the USA, woody peat is also formed, very similar to fossil lignite.

With stronger decomposition and change in plant residues, it creates brown coal. Its color is dark brown or black; It is stronger than lignite, wood remains are less common in it and it is more difficult to discern them. When burned, brown coal produces more heat than lignite because it is richer in carbon. Brown coal does not always turn into hard coal over time. It is known that brown coal from the Moscow basin is of the same age as hard coal in western slope Urals (Kizelovsky basin). The process of turning brown coal into hard coal occurs only when layers of brown coal descend into deeper horizons earth's crust or mountain building processes occur. To transform brown coal into hard coal or anthracite, very high temperatures and high pressure are needed in the bowels of the Earth. IN coal plant remains are visible only under a microscope; it is heavy, shiny and often very strong. Some types of coal themselves or together with other varieties are coked, that is, they turn into coke.

Black shiny coal contains the largest amount of carbon - anthracite. You can find plant remains in it only under a microscope. When burned, anthracite produces more heat than all other types of coal.

Boghead- dense black coal with a conchoidal fracture surface; when dry distilled, it produces a large amount of coal tar - a valuable raw material for the chemical industry. Boghead is formed from algae and sapropel.

The longer coal lies in the earth's layers or the more it is exposed to pressure and deep heat, the more carbon it contains. Anthracite contains about 95% carbon, brown coal contains about 70%, and peat contains from 50 to 65%. In the swamp, where peat initially accumulates, clay, sand and various dissolved substances usually fall along with water. They form mineral impurities in peat, which then remain in coal. These impurities often form interlayers that divide the coal layer into several layers. The impurity contaminates the coal and makes it difficult to mine.

When coal is burned, all mineral impurities remain in the form of ash. The better the coal, the less ash it should contain. In good types of coal it is only a few percent, but sometimes the amount of ash reaches 30-40%. If the ash content is more than 60%, then the coal does not burn at all and is not suitable for fuel.

Coal seams are different not only in their composition, but also in structure. Sometimes the entire thickness of the seam consists of pure coal. This means that it was formed in a peat bog, where almost no water, contaminated with clay and sand, entered. Such coal can be burned immediately. More often, coal layers alternate with clay or sandy layers. Such coal seams are called complex. In them, for example, a layer 1 m thick often contains 10-15 layers of clay, each several centimeters thick, while pure coal accounts for only 60-70 cm; Moreover, the coal can be of very good quality. To obtain fuel from coal with a low content of foreign impurities, coal is enriched. The rock from the mine is immediately sent to the processing plant. There, the rock extracted from the mine is crushed into small pieces in special machines, and then all clay lumps are separated from the coal. Clay is always heavier than coal, so the mixture of coal and clay is washed with a stream of water. The strength of the jet is chosen such that it carries out the coal, while the heavier clay remains at the bottom. Then the water and coal are passed through a fine grate. The water drains, and the coal, already clean and free of clay particles, collects on the surface of the grate. This type of coal is called enriched coal. There will be very little ash left in it. It happens that the ash in the coal is not harmful impurity, but minerals. For example, fine, clayey mud carried into a swamp by streams and rivers often forms layers of valuable fire-resistant clay. It is specially developed or the ash remaining after the combustion of coal is collected, and then used to make porcelain tableware and other products. Sometimes coal is found in the ashes

Its use is so multifunctional that sometimes you are simply amazed. At such moments, doubt involuntarily creeps in, and a completely logical question sounds in your head: “What? Is this all coal?!” Everyone is accustomed to thinking of coal as just a combustible material, but, in fact, its range of uses is so wide that it seems simply incredible.

Formation and origin of coal seams

The appearance of coal on Earth dates back to the distant past Paleozoic era, when the planet was still in the development stage and had a completely alien appearance to us. The formation of coal seams began approximately 360,000,000 years ago. This happened mainly in the bottom sediments of prehistoric reservoirs, where organic materials accumulated over millions of years.

Simply put, coal is the remains of the bodies of giant animals, tree trunks and other living organisms that sank to the bottom, decayed and were pressed under the water column. The formation process of deposits is quite long, and it takes at least 40,000,000 years to form a coal seam.

Coal mining

People have long understood how important and irreplaceable it is, and its use has been able to be appreciated and adapted on such a large scale relatively recently. Large-scale development of coal deposits began only in the 16th-17th centuries. in England, and the mined material was used mainly for smelting cast iron necessary for the manufacture of cannons. But its production by today’s standards was so insignificant that it could not be called industrial.

Large-scale mining began only towards the middle of the 19th century, when developing industrialization simply needed coal. Its use, however, at that time was limited exclusively to combustion. There are now hundreds of thousands of mines operating all over the world, producing more per day than in several years in the 19th century.

Types of coal

Deposits of coal seams can reach a depth of several kilometers, extending into the thickness of the earth, but not always and not everywhere, because it is both in content and in appearance heterogeneous

There are 3 main types of this fossil: anthracite, brown coal, and peat, which very vaguely resembles coal.

Anthracite is the oldest formation of its kind on the planet, middle age this species is 280,000,000 years old. It is very hard, has a high density, and its carbon content is 96-98%.

Hardness and density are relatively low, as is its carbon content. It has an unstable, loose structure and is also oversaturated with water, the content of which can reach up to 20%.

Peat is also classified as a type of coal, but it has not yet formed, so it has nothing to do with coal.

Properties of coal

Now it is difficult to imagine another material more useful and practical than coal, the basic properties and application of which deserve the highest praise. Thanks to the substances and compounds it contains, it has become simply irreplaceable in all areas of modern life.

The component of coal looks like this:

All these components make coal, the application and use of which is so multifunctional. The volatile substances contained in coal ensure rapid ignition and subsequent achievement of high temperatures. The moisture content simplifies the processing of coal, its caloric content makes it indispensable in pharmaceuticals and cosmetology, ash itself is a valuable mineral material.

The use of coal in the modern world

The uses of minerals vary. Coal was initially only a source of heat, then energy (it turned water into steam), but now in this regard, the possibilities of coal are simply unlimited.

Thermal energy from burning coal is converted into electricity, coke products are made from it and liquid fuel is extracted. Coal is the only rock that contains rare metals such as germanium and gallium as impurities. From it they extract benzene, which is then processed into benzene, from which coumarone resin is extracted, which is used to make all kinds of paints, varnishes, linoleum and rubber. Phenols and pyridine bases are obtained from coal. When processed, coal is used in the production of vanadium, graphites, sulfur, molybdenum, zinc, lead and many other valuable and now irreplaceable products.

Anthracite is the oldest of fossil coals, coal is the most high degree carbonization.

Characterized by high density and shine. Contains 95% carbon. It is used as a solid high-calorie fuel (calorific value 6800-8350 kcal/kg).

Coal

Coal- sedimentary rock, which is a product of deep decomposition of plant remains (tree ferns, horsetails and mosses, as well as the first gymnosperms). Most coal deposits were formed during the Paleozoic, predominantly the Carboniferous period, approximately 300-350 million years ago.

By chemical composition coal is a mixture of high molecular weight polycyclic aromatic compounds with high mass fraction carbon, as well as water and volatile substances with small amounts of mineral impurities, which form ash when burning coal. Fossil coals differ from each other in the ratio of their constituent components, which determines their heat of combustion. Row organic compounds, which are part of coal, have carcinogenic properties. The carbon content of coal, depending on its type, ranges from 75% to 95%.

Brown coal

Brown coal- hard fossil coal, formed from peat, contains 65-70% carbon, has a brown color, the youngest of fossil coals. It is used as a local fuel and also as a chemical raw material.

Coal formation

For the formation of coal, abundant accumulation of plant matter is necessary. In ancient peat bogs, starting from the Devonian period, organic matter accumulated, from which fossil coals were formed without oxygen. Most commercial fossil coal deposits date from this period, although younger deposits also exist. The oldest coals are estimated to be about 350 million years old.

Coal is formed when decaying plant material accumulates faster than bacterial decomposition occurs. The ideal environment for this is created in swamps, where Still water, depleted of oxygen, prevents the activity of bacteria and thereby protects the plant mass from complete destruction. At a certain stage of the process, the acids released during the process prevent further bacterial activity. This is how it arises peat- the initial product for the formation of coal. If it is then buried under other sediments, the peat experiences compression and, losing water and gases, is converted into coal.

Under the pressure of sediment layers 1 kilometer thick, a 20-meter layer of peat produces a layer of brown coal 4 meters thick. If the depth of burial of plant material reaches 3 kilometers, then the same layer of peat will turn into a layer of coal 2 meters thick. At greater depths, about 6 kilometers, and at higher temperatures, a 20-meter layer of peat becomes a layer of anthracite 1.5 meters thick.

Proven coal reserves

Coal in Russia

Types of coal

In Russia, depending on the stage of metamorphism, they distinguish: brown coals, bituminous coals, anthracites and graphites. Interestingly, in Western countries there is a slightly different classification: respectively, lignites, subbituminous coals, bituminous coals, anthracites and graphites.

1. Brown coals. They contain a lot of water (43%) and therefore have low heat combustion. In addition, they contain a large amount of volatile substances (up to 50%). They are formed from dead organic residues under load pressure and under the influence of elevated temperature at depths of about 1 kilometer.
2. Stone coals. They contain up to 12% moisture (3-4% internal), therefore they have a higher calorific value. They contain up to 32% volatile substances, due to which they ignite well. They are formed from brown coal at depths of about 3 kilometers.
3. Anthracites. Almost entirely (96%) consists of carbon. They have the highest heat of combustion, but do not ignite well. They are formed from coal when pressure and temperature increase at depths of about 6 kilometers. Mainly used in the chemical industry

History of coal mining in Russia

Becoming coal industry in Russia dates back to the first quarter of the 19th century, when the main coal basins had already been discovered.

Dynamics of fossil coal production volumes in Russian Empire you can see .

Coal reserves in Russia

5.5% is concentrated in Russia (why is there such a difference with the percentage of proven coal reserves as of 2006? - because most of it is not suitable for development - Siberia and permafrost) world coal reserves, amounting to more than 200 billion tons. Of these, 70% are brown coal reserves.

• In 2004, 283 million tons of coal were produced in Russia. 76.1 million tons were exported.
• In 2005, 298 million tons of coal were produced in Russia. 79.61 million tons were exported.

In Russia in 2004, there was a shortage of coking coal grades “Zh” and “K” of at least 10 million tons (VUKHIN estimate), which was associated with the retirement of mining capacities in Vorkuta and Kuzbass.

Largest promising deposits

Elginskoye field(Sakha). Owned by Mechel OJSC. The most promising object for open-pit mining is located in the southeast of the Republic of Sakha (Yakutia), 415 km east of the city of Neryungri. The field area is 246 km². The deposit is a gently sloping brachysynclinal asymmetrical fold. The deposits of the Upper Jurassic and Lower Cretaceous are carbon-bearing. The main coal seams are confined to the deposits of the Neryungri (6 seams with a thickness of 0.7-17 m) and Undyktan (18 seams with a thickness of also 0.7-17 m) formations. Most of the coal resources are concentrated in four seams y4, y5, n15, n16 usually complex structure. The coals are mostly semi-shiny lenticular-banded with a very high content of the most valuable component - vitrinite (78-98%). According to the degree of metamorphism, coals belong to the III (fat) stage. Coal grade Zh, group 2Zh. Coals are medium- and high-ash (15-24%), low-sulfur (0.2%), low-phosphorus (0.01%), well-caking (Y = 28-37 mm), with a high calorific value (28 MJ/kg). Elga coal can be enriched to the highest world standards and produce export coking coal high quality. The deposit is represented by thick (up to 17 meters) gently sloping seams with overlying sediments of low thickness (the stripping ratio is about 3 cubic meters per ton of raw coal), which is very beneficial for organizing open-pit mining.

Elegestskoye field(Tuva) has reserves of about 1 billion tons of coking coal of the scarce grade “Zh” (the total volume of reserves is estimated at 20 billion tons). 80% of the reserves are located in one seam 6.4 m thick (the best mines in Kuzbass work in seams 2-3 m thick, in Vorkuta coal is mined from seams thinner than 1 m). After reaching its design capacity by 2012, Elegest is expected to produce 12 million tons of coal annually. The license to develop Elegest coals belongs to the Yenisei Industrial Company, which is part of the United Industrial Corporation (UPK). On March 22, 2007, the Government Commission on Investment Projects of the Russian Federation approved the implementation of projects for the construction of the Kyzyl-Kuragino railway line in conjunction with the development of the mineral resource base of the Republic of Tuva.

The largest Russian coal producers

Coal gasification

This direction of coal utilization is associated with its so-called “non-energy” use. We are talking about the processing of coal into other types of fuel (for example, into combustible gas, medium-temperature coke, etc.), preceding or accompanying the production of thermal energy from it. For example, in Germany during the Second World War, coal gasification technologies were actively used to produce motor fuel. In South Africa, at the SASOL plant, using layered gasification technology under pressure, the first developments of which were also carried out in Germany in the 30-40s of the 20th century, more than 100 types of products are currently produced from brown coal. ( This process gasification is also known as the "Lurgi method".)

In the USSR, coal gasification technologies, in particular, were actively developed at the Research and Design Institute for the Development of the Kansk-Achinsk Coal Basin (KATEKNIIugol) in order to increase the efficiency of the use of Kansk-Achinsk brown coals. The Institute's staff have developed a number of unique technologies for processing low-ash brown and hard coals. These coals may be subject to energy technology processing into such valuable products as medium temperature coke, capable of serving as a substitute for classic coke in a number of metallurgical processes, flammable gas, suitable, for example, for combustion in gas boilers as a substitute for natural gas, and synthesis gas, which can be used in the production of synthetic hydrocarbon fuels. Combustion of fuels obtained as a result of energy-technological processing of coal provides a significant gain in performance harmful emissions relative to the combustion of the original coal.

After the collapse of the USSR, KATEKNIIugol was liquidated, and the institute’s employees involved in the development of coal gasification technologies created their own enterprise. In 1996, a plant for processing coal into sorbent and flammable gas was built in Krasnoyarsk ( Krasnoyarsk region, Russia). The plant is based on a patented technology of layered coal gasification with reverse blast (or reverse process of layered coal gasification). This plant is still operating today. Due to the exceptionally low (compared to traditional coal combustion technologies) emissions of harmful emissions, it is freely located near the city center. Subsequently, based on the same technology, a demonstration plant for the production of household briquettes was also built in Mongolia (2008).

It is worth noting some characteristic differences between the layered coal gasification technology with reverse blast and the direct gasification process, one of the varieties of which (pressure gasification) is used at the SASOL plant in South Africa. The combustible gas produced in the reverse process, unlike the direct process, does not contain coal pyrolysis products, therefore, complex and expensive gas purification systems are not required in the reverse process. In addition, in the reverse process it is possible to organize incomplete gasification (carbonization) of coal. In this case, two useful products are produced at once: medium-temperature coke (carbonate) and combustible gas. The advantage of the direct gasification process, on the other hand, is its higher productivity. During the period of the most active development of coal gasification technologies (the first half of the 20th century), this led to an almost complete lack of interest in the reverse process of layered coal gasification. However, at present, market conditions are such that the cost of medium-temperature coke alone, produced in the reverse process of coal gasification (carbonization), makes it possible to compensate for all the costs of its production. By-product is a flammable gas suitable for combustion in gas boilers to obtain thermal and/or electrical energy, - in this case has a conditionally zero cost. This circumstance ensures the high investment attractiveness of this technology.

Another well-known technology for the gasification of brown coal is the energy-technological processing of coal into medium-temperature coke and thermal energy in an installation with a fluidized (boiling) bed of fuel. An important advantage of this technology is the possibility of its implementation by reconstructing standard coal boilers. At the same time, the boiler’s thermal energy performance remains at the same level. A similar project for the reconstruction of a standard boiler was implemented, for example, at the Berezovsky open-pit mine (Krasnoyarsk Territory, Russia). In comparison with the layered coal gasification technology, the energy-technological processing of coal into medium-temperature coke in a fluidized bed is characterized by significantly higher (15-20 times higher) productivity.

This article provides information about an interesting sedimentary rock that is a source of great economic importance. This rock, amazing in the history of its origin, is called “hard coal”. His education is quite interesting. It should be noted that, despite the fact that this rock makes up less than one percent of all sedimentary rocks existing on earth, it has great value in many areas of people's lives.

General information

How was coal formed? Its formation includes many processes occurring in nature.

Coal appeared on Earth approximately 350 million years ago. To explain it in a simple way, it happened as follows. Tree trunks, falling into the water with other vegetation, gradually formed huge layers of organic, undecomposed mass. The limited access of oxygen did not allow this mess to decompose and rot, which gradually sank deeper and deeper under its weight. Over a long period of time and due to the displacement of layers of the earth's crust, these layers went to a considerable depth, where, under the influence of elevated temperatures and high pressure, this mass was converted into coal.

Below we will take a closer look at how coal appeared, the formation of which is very interesting and curious.

Types of coal

Modern coal deposits around the world produce different types coal:

1. Anthracite. These are the hardest varieties, mined from great depths and having the highest combustion temperature.

2. Coal. Many of its varieties are mined in open pits and mines. This type is the most common in areas of human activity.

3. Brown coal. This is the youngest species, formed from peat residues and has the lowest combustion temperature.

All of the listed forms of coal lie in layers, and the places where they accumulate are called coal basins.

Theories of the origin of coal

What is coal? Simply put, this sediment is accumulated, compacted and processed plants over time.

There are two theories, the more popular of which is the one that many geologists adhere to. It is as follows: the plants that make up coal accumulated in large peat or freshwater swamps for many thousands of years. This theory assumes the growth of vegetation in the place where the rocks were discovered and is called “autochthonous”.

Another theory is based on the fact that coal seams accumulated from plants transported from other places, which were deposited in a new area under flood conditions. In other words, coal originated from transported plant debris. The second theory is called allochthonous.

In both cases, the source of coal formation is plants.

Why is this stone burning?

Basic chemical element in the coal, possessing beneficial properties, - carbon.

Depending on the conditions of formation, processes and age of the layers, each coal deposit contains its own certain percentage of carbon. This indicator determines the quality of natural fuel, since the level of heat transfer is directly related to the amount of carbon oxidized during combustion. The higher the calorific value of a given rock, the more suitable it is as a source of heat and energy.

What is coal for people around the world? First of all, this is the best fuel, suitable for various spheres of life.

About fossils in coal

The fossil plant species found in coal do not support the autochthonous theory of origin. Why? For example, moss trees and giant ferns, characteristic of the coal deposits of Pennsylvania, could grow in swampy conditions, while other fossil plants of the same basin (conifers or giant horsetail, etc.) preferred drier soils rather than swampy places. It turns out that they were somehow transported to these places.

How did coal come into being? Its formation in nature is amazing. Marine fossils such as molluscs, fish and brachiopods (or brachiopods) are also common in coal. In coal seams there are also coal balls (rounded, crumpled masses of perfectly preserved fossil plants and animals, including marine ones). For example, the small annelid sea worm is commonly found attached to plants in coals North America and Europe. They belong to the Carboniferous period.

The occurrence of marine animals interspersed with non-marine plants in coal sedimentary rocks indicates that they mixed during the movement. Amazing and lengthy processes took place in nature before coal was finally formed. Its formation in this way confirms the allochthonous theory.

Amazing Finds

The most interesting finds in the coal layers are tree trunks lying vertically. They often cross huge strata of rock perpendicular to the coal bedding. Trees in this vertical position are often found in layers associated with coal deposits, and a little less often in the coal itself. Many are of the opinion about moving tree trunks.

The amazing thing is that sediment had to accumulate so quickly to cover these trees before they deteriorated (rotted) and fell.

That's pretty interesting story formation of a rock called coal. The formation of such layers in the bowels of the earth is a reason for further research in search of answers to numerous questions.

Where do the lumps in coal come from?

Impressive external feature coal is the content of huge lumps in it. These large blocks have been found in coal seams of many deposits for more than a hundred years. The average weight of 40 lumps collected from the West Virginia coalfield was about 12 pounds, and the largest was 161 pounds. Moreover, many of them were metamorphic or volcanic rock.

Researcher Price suggested that they could have been transported to the coal deposits in Virginia from afar, entwined in the roots of trees. This conclusion also supports the allochthonous model of coal formation.

Conclusion

Many studies prove the truth of the allochthonous theory of coal formation: the presence of remains of terrestrial and marine animals and plants implies their movement.

Studies have also proven that the metamorphism of this rock does not require a long time (millions of years) of exposure to pressure and heat - it can also form as a result of rapid heating. And trees located vertically in coal sediments confirm the rather rapid accumulation of vegetation remains.