It is more or less well known that the material commonly called iron, even in the simplest case, is an alloy of iron itself, as a chemical element, with carbon. At a carbon concentration of less than 0.3%, a soft ductile refractory metal is obtained, behind which the name of its main ingredient, iron, is assigned. An idea of ​​the iron that our ancestors dealt with can now be obtained by examining the mechanical properties of the nail.

At a carbon concentration of more than 0.3%, but less than 2.14%, the alloy is called steel. In its original form, steel resembles iron in its properties, but, unlike it, it can be hardened - with sudden cooling, steel acquires greater hardness - a remarkable advantage, however, almost completely negated by brittleness acquired during the same hardening.

Finally, at a carbon concentration above 2.14%, we get cast iron. Brittle, fusible, well suited for casting, but not amenable to forging, metal.

One of the determining conditions for the start of metal production is knowledge of the minerals containing this metal. These minerals should be noticeable, draw attention to themselves, both by their peculiar appearance and by some specific properties that ancient man could be used, including in archaic thermal processes. All iron minerals, which are discussed in detail below, fully possess similar external data and properties.

The history of primitive human society was inextricably linked with stone and stone products. The most primitive of these products were ordinary river pebbles, chipped at one end. The age of the oldest stone tools dates back to a period of about 2.5 million years.

At first, our ancestors used any pebble. However, developing new territories, they began to show interest in a wide variety of rocks. It is difficult to say when primitive man learned to distinguish between them, but the fact that flint became his favorite stone throughout the Anthropogen is known for certain. This predilection is due to the amazing properties of flint - its ability, with directed impacts, not to break into pieces, but to give thin flakes and plates with sharp edges. Having beaten the stone from different sides, the ancient man received a hand ax and many sharp flakes. Both were used: axes were used for processing wood, flakes - for cutting meat.

A lot of time passed before a person learned to separate plates from flint stones. This required the development of certain skills in stone processing. Splitting the stone, the ancient master received one or more plates - an excellent material for making spearheads, scrapers and knife-like tools. It was in flint that the form of such well-known tools as an ax, a sickle, a knife, a hammer was first found and embodied.

Jasper, a strong and very hard rock, obsidian and jade also had high consumer properties. However, these stones were and are found in nature much less frequently than flint.

2.2.1 Goethite (α-Fe) (hydrogoethite, limonite, brown ironstone)

This mineral got its name in honor of I. V. Goethe, a brilliant poet, and, in addition, an outstanding naturalist and connoisseur of minerals. Probably, it was he, in all the variety of his manifestations, who became the first ore from which people learned to extract iron.

Figure 10 - Goethite

On the earth's surface, iron in the divalent form is slowly leached from rocks by soil and river waters containing plant humic acids. In meadows and other open places, in oxygen-saturated lake water, it oxidizes to trivalent and precipitates in the form of insoluble goethite, forming “lake”, “meadow” and “turf” ores. From here comes another name for goethite - limonite - from the Greek word "leimon", which means "wet meadow" or "swamp" (Figures 11.12).

Strictly speaking, limonite is not a mineral, but a mixture of various minerals - iron hydroxides, of which goethite is the main one. In essence, limonite is “natural rust”, from where (for its characteristic rusty-brown color) its other name “brown iron ore” comes from. It is in swamps, lakes and in the shallow sea that unusual-looking limonite ores appear (Figure 13). The limonite of such ores resembles beans or small bird eggs. Therefore, such names of limonite as "bean ore" or "pea stone" have become widespread. Goethite is also found in the form of loose ocher staining the hand, in the form of lacquered black clusters and buds, and cascades of icicles, and gently velvet covers and pillows in cracks and caves, and in the form of brilliant fans and diamond-black or red needles and hairs in crystals. amethyst - all these are iron hydroxides, that is, all this is goethite or hydrogoethite. In addition, goethite is distributed in the form of a "glass head" - beautiful spherulitic crusts with a lacquer-black surface.

Figure 11 - Extraction of "lake" ores Figure 12 - Extraction of "meadow" ores

Figure 13 - Swamp ore

2.2.2 Hematite (Fe 2 O 3)

Hematite is a mineral with a beautiful shape, sparkling facets, color from steel to iron black, with a special reddish tint that clearly distinguishes hematite from similar minerals (Figure 14). The modern name of this mineral is first found in Theophrastus (naturalist and philosopher who lived in 372–287 BC and wrote the treatise “On Stones”). It comes from the Greek word "hema" - blood, which is associated with the cherry or wax-red color of the mineral powder, as well as the synonyms of hematite - "bloody", "red iron ore". Another ancient synonym for hematite is “iron shine”. Hematite crystals have high hardness and density, strong semi-metallic luster, cherry red color. Special shiny tabular crystals used to be called "specularite", and thin-plate, sometimes collected in parallel packages, - "iron mica".

Figure 14 - Hematite

Spherulite crusts of hematite are quite common; in the old days, German miners called them "glass head". Incomparably less common is another form of splitting of hematite crystals - the "iron rose", where lamellar crystals are arranged like cards in an unfolded deck. "Iron roses" are valued along with the most expensive minerals.

Hematite is also found in dense masses, in a kind of powdery secretions ("iron sour cream"), and most of all - in the form of granular inclusions in various rocks. In significant quantities, it is released during volcanic processes. A fact is known when in 1817, during the eruption of Vesuvius, a meter-long layer of hematite was formed in just 10 days. Dense hematite is an excellent mineral for carving various figures.

It is from hematite that the word "gemma" is derived, denoting a carved stone. In ancient Egypt and Babylon, carved hematite was widely used as jewelry; in ancient Greece, carved stones in their own way served as locks and keys. Everything that we used to lock up, the Greeks sealed with a personal seal. Hematite and chalcedony were most often used to make such in-depth seals.

Another area of ​​application of hematite was medicine. The famous physician of antiquity Dioscurus named hematite among the five main stones for healing (with amber, lapis lazuli, jade and malachite). Hematite was attributed the ability to heal bleeding wounds, heal diseases Bladder and venereal diseases.

The fine powder of hematite "crocus" was used in ancient times for polishing gold and silver items. It should be noted that the abrasive properties of the mineral, unlike medical ones, have not lost their significance to this day.

It is believed that the first purpose of hematite was its use in the form of mineral paint. The oldest find of hematite paints in human burials dates back to about 40 thousand years BC.

Red hematite paint - a mummy - was an indispensable component of mummification among the ancient Egyptians (hence its name). Hematite amulets were placed in a strictly defined order between the bandages of the mummies of the pharaohs. Until the Middle Ages, ocher was the only yellow paint. It was made by mixing hematite with chalk. Later, yellow paint began to be made from a mixture of lead oxide with red lead.

Finally, the amazing crystals of bloodstone (“scorpion stone”) found special use in medieval magic. Only with a ring with a bloodstone on his finger could a medieval magician dare to call the spirits of the dead to communion.

2.2.3 Siderite (FeCO 3)

Another contender for the title of the first iron ore mineral in the history of mankind is siderite. Its natural manifestations are perhaps the least spectacular among other iron ores. They are usually buds, concretions, or oolitic (spherical) textures of numerous brown-yellow hues (Figure 15).

Figure 15 - Siderite

The name of the mineral comes from the Greek word "sideros" - iron (which, in turn, also means a star, i.e. iron is a stellar metal - a metal that comes from the sky). There is another version of the origin of the word "sideros", which has become widespread in recent decades. According to this version, the Greek "sideros" is of Caucasian origin from the root "sido", which means "red". An important circumstance confirming this version is the generally recognized fact that the birthplace of ore iron is Asia Minor, from where, through the legendary people of blacksmiths - Halibers, the ancient Greeks also learned about iron. From here comes another name for the mineral - halibit. Other common names: gyrite, flints, iron spar, white ore. Siderite ores played a particularly important role in the development of iron metallurgy in the early Middle Ages, when the Alpine region became the main center of its production. It is in the Alps that the famous deposits of siderite are located: Neudorf and Eruberg, as well as the famous "mountain" - Eisenerz.

2.2.4 Pyrite and marcasite (FeS 2)

The name "pyrite" comes from the Greek word "pyros" - fire, fire-like.

A blow to it gives rise to sparks, so in ancient times, pieces of pyrite served as an ideal flint. The mineral received its second name "pyrite" in the 16th century. - it was assigned to pyrite by the outstanding German scientist Agricola (Georg Bauer) and also has Greek roots, since it comes from the name of the Greek peninsula of Chalkidiki, rich in various ores. Subsequently, the name "pyrite" was extended to the entire class of sulfides similar to pyrite, and pyrite itself was called iron or sulfur pyrite.

The yellow color of pyrite is sometimes masked by a brown or variegated tint, tk. it often contains impurities of arsenic, cobalt, nickel, less often - copper, gold, silver. The most characteristic in the appearance of a mineral is the shape of its crystals - most often it is a cube (Figure 16). The largest known pyrite crystal, measuring 50 cm along the edge, was found near the city of Xanthi in northeastern Greece. AT ancient india pyrite crystals served as an amulet that protected from crocodiles.

Figure 16 - Pyrite

In nature, pyrite is widely distributed and very noticeable. It literally catches the eye with its golden color, bright brilliance of almost always clean edges, clear crystalline forms. For these reasons, pyrite has been known since ancient times. In color and luster, it resembles brass, and even gold, for which it once earned the condescending nickname "cat's gold." Polished pyrite shines even brighter. The ancient Incas made mirrors from polished pyrite. The oldest known pyrite deposits are Rio Tinto and Novohun (Spanish Pyrenees), Rio Marina (Elba Island), Ural Mountains.

Amazing property pyrite is the replacement of its crystals in the reducing environment of organic remains. In this case, spectacular fossils are formed: pyritized shells, pieces of wood, and even whole fragments of trunks and other parts of plants, etc. The replacement process can go very vigorously: in the well-known case of the “Falun man”, the body of a miner who died in a deep (130 m) working was completely replaced by pyrite in just 60 years. At the same time, the appearance of a person was completely preserved. Perhaps this is where the famous legend of the "stone guest" comes from, known to many peoples of the world.

Marcasite has the same chemical composition as pyrite, but a different crystal structure and is much rarer than pyrite. In ancient times, pyrite and marcasite were identified. The German miners of the late Middle Ages, calling both of these minerals sulfur pyrites, nevertheless singled out marcasite in a special variety of "spear-shaped", "radiant", "comb" pyrites.

Only in 1814 it was established that marcasite is a special mineral, and in 1845. its first scientific description was compiled and the name "marcasite" was fixed. The ancient Arabic "marcasite" originally also meant pyrite, antimony and bismuth. Jewelers still refer to pyrite as "marcasite".

2.2.5 Magnetite (Fe 3 O 4)

Magnetite is a very heavy mineral with a semi-metallic "dull" luster, iron-black in color, with a blue or iridescent tint. Magnetite is characterized by black-gray crystals (Figure 17). According to one of the legends, magnetite was named after the Greek shepherd Magnes. Magnes was grazing his flock on one of the inconspicuous plateaus in Thessaly, and suddenly his iron-tipped staff and his sandals lined with nails were pulled to itself by a mountain composed of solid gray stone. It is magnetism that is the rarest distinguishing property of magnetite among minerals.

Figure 17 - Magnetite

Many scientists and poets wrote about magnetite ancient world and the Middle Ages: Aristotle dedicated a special essay to him (“On the Magnet”), Lucretius and Claudian described in verse, in the fairy tales “A Thousand and One Nights” it is told about a magnetic mountain in the middle of the sea, the force of attraction of which was so great that it pulled out nails from ships, which immediately collapsed and sank.

However, the real use of the magnet, apparently, was first found in China, where in the II century. BC. compass was invented. The oldest known compasses in the countries of the East looked like a small cart on which an iron man sat and pointed south with his outstretched hand.

Thus, long before the discovery of metals, iron minerals attracted the attention of man and were widely used by him. Therefore, it can be confidently asserted that the “accidental” discovery of a method for smelting iron from ore was well prepared by the entire previous history of the development of civilization.

Iron ore is an important mineral product that mankind began to extract many centuries ago. Since ancient times, iron has been widely used in domestic and other conditions of human society. One of the key advantages and properties of iron ore is the ability to manufacture steel obtained during its smelting.

Iron ore can have different properties, mineral composition, as well as the percentage of impurities and metals, depending on the type and place of its development. Finding iron ore mining sites with the appropriate technical equipment is not a difficult task, since iron makes up more than 5% of the solid deposits of the earth's crust over the entire surface of the planet. According to Wikipedia and other reliable sources, iron ore is the fourth most common mineral mined in the world.

However, find this metal in nature in pure form it is not possible - it can be found in certain quantities in most known types and types of stone (rocks). Minerals (iron ore) are among the most profitable in terms of extraction. The quantitative content of iron in it depends on the nature of the origin of iron ore.

What does iron ore look like and what is it?

As a key chemical element, iron is found in many rocks. However, not every such rock can be a potential raw material for mining and development. The feasibility of developing iron ores, as such, largely depends on the percentage composition.

Its mining was closely engaged more than 3 thousand years ago, due to the ability to make iron-based products of better quality and durability in comparison with bronze and copper, which began to be mined even earlier. Already in those days, the craftsmen who worked with the smelters could accurately distinguish between the types of iron ore.

Currently, it is customary to distinguish several types of raw materials suitable for the subsequent smelting of useful metal:

• magnetine;
• magnetino-apatite;
• magnetino-titanium;
• hydrogoethite-goethite;
• hematite-magnetine.

A rich iron ore deposit is considered with a percentage of iron content of 57%. But, as mentioned above, it may be expedient to develop deposits in which the ore contains 26% of this useful metal. In the composition of rocks, iron prevails in the form of oxides. The remaining constituents are phosphorus, sulfur and silica.

There are tables of iron ore, which reflect its raw material, chemical composition and percentage of iron. If we are guided by the numerical indicators of most of these tables, then it is conditionally possible to divide valuable ores according to the degree of their richness and properties into 4 categories

• very rich - the content of the base metal is more than 65%;
• moderately rich - the average percentage of iron is 60-65%;
• moderate - from 45% or more;
• the poor - less than 45% of the mined useful elements in general.

Depending on the amount of side impurities that make up the iron deposit being developed, more or less energy is required for processing. The efficiency of production of finished products based on iron largely depends on this.

Nature of origin

Most of the known mine types were formed under the influence of three main factors. The features and characteristics of iron ore, in fact, depend on them.

Magmatic formation. Magmatic compositions were formed under the influence of high temperatures of magma or under the condition of high activity of ancient volcanoes. In fact, natural processes of mixing and remelting of rocks took place.

This kind of minerals is a crystalline mineral fossil compounds that differ a high percentage iron content. Deposits of igneous minerals, as a rule, can be found in zones of ancient formation of mountainous areas. It was in these places that the molten substances approached as close as possible to the surface layers of the soil.

metamorphic formation. In the process of such formation, sedimentary-type minerals are formed. The essence of this process is reduced to the movement of individual sections of the Earth's crust, in which certain layers, rich in certain elements, fall under the rocks that lie above.

Minerals, which were formed during the next movement, migrate closer to the earth's surface. Iron ore, which is formed during metamorphic formation, usually has a high percentage of useful metal compounds and is not located too deep from the surface. One of the most common examples is magnetic iron ore, containing up to 75% iron in its composition.

Sedimentary formation. AT this case the main factors in this type of mine formation are the natural forces of nature, in particular winds and water. The rock layers are destroyed and moved to the lowlands - it is here that they accumulate, forming separate layers. Water acts as a reagent, which leaches the starting materials. In the course of such processes, deposits of brown iron ore are formed, which is a crumbly, loosened mass with a high content of mineral impurities and a percentage of iron up to 35-40%.

Due to the different specifics of the formation of metamorphic rocks, the raw material is often mixed inside the layers with igneous rock, limestone and clay. In the same deposit, indicated by the corresponding sign on the map, deposits of different origin are found, which are mixed with each other. Places supposedly rich in sedimentary iron ores in this case are determined in the course of geological exploration activities.

Basic properties and types. What ore is iron made from?

The most common type is usually referred to as red iron ore, the basis of which is hematite oxide. It contains a minimum of side impurities and over 70% iron.

The next most common is brown iron ore (limonite), which is an iron oxide containing H 2 O in its composition. As a rule, about a quarter of the percentage of iron is included in the composition of limonite. In nature, brown iron ore can be found in the form of porous, loose rocks containing phosphorus and manganese. Ore contains clay as waste rock.

Magnetic iron ore contains magnetic oxide, the properties of which are lost under conditions of strong heating. In nature, it is found much less frequently than the above rocks and, in terms of the percentage of iron, in some cases is not inferior to red iron ore.

Spar iron ore is an ore rock containing siderite with a high content of clay in the composition. This is a very rare breed, and due to the low content of iron, it is mined much less often, especially when it comes to industrial use.

In addition to oxides, there are other types of iron ore, which are based on carbonates and silicates.

Geographic location of key fields

All major deposits are usually divided into:

1. Metamorphogenic - quartzite deposits;
2. Exogenous - brown iron ore and other sedimentary rocks;
3. Endogenous - predominantly titanomagnetite compositions.

Similar ore deposits are found on almost every continent. Most of the iron ore deposits are located on the territory of the CIS countries, in particular, this is the territory of Kazakhstan, Russia and Ukraine. Sufficiently large reserves of iron ore accumulations can boast of such states as South Africa, India, USA, Australia, Canada and Brazil. There are maps of iron ore deposits, both on a global scale and with a more detailed indication of deposits on the territory of a particular state.

The value of iron ore and the areas in which it is used

Predominantly all industries in which these minerals are involved are associated with the metallurgical sector. For the most part, iron ore is used in the smelting of iron using a converter or open-hearth furnace. In turn, cast iron is widely used in many industrial sectors.

Today, another super-strong, anti-corrosion alloy, steel, is also extremely popular and actively produced, for which iron ore minerals are also used. It is the most popular industrial alloy and is renowned for its corrosion resistance and high strength.

Steel and cast iron materials are used in the following industries:

• rocket-building and military industry, production of special equipment;
• mechanical engineering, including the manufacture of machine tools and other factory mechanisms;
• automotive production (car frames, engine elements, housings and other mechanical components are manufactured);
• mining industry (production of heavy mining equipment and other special equipment);
• construction - reinforcing materials, the creation of a supporting frame.

Mining methods

Methods and means of extracting ore minerals from the bowels depend on the depth at which the desired material occurs. In this context, it is customary to distinguish three main methods:

Borehole method (hydro extraction) - to work in this way, specialists drill wells that reach rock layers. Tubular structures are placed in the formed sections, through which the material is crushed and extracted with a powerful water jet. This is the least effective, stagnant and outdated method, which is rarely used these days.

Shaft method - is used provided that the layers lie deeper (up to 900 meters). First of all, mine alignments are cut through - drifts are developed from them along the seam. The rock is crushed and brought to the surface by special conveyors.

Career method - unlike the borehole, is considered the most common. It is used to work at medium depth (up to 300 meters). For development, powerful excavators and mechanisms that crush the rock are used. After crushing, the material is shipped and transported directly to the processing plant.

How are iron ore enriched?

Due to the existence various types ores according to the degree of how much iron is contained in the ore, less enriched materials are sent to special plants, where they are sorted, crushed, separated and agglomerated.

In general, there are 4 main methods of ore enrichment:

Flotation. A specially prepared dusty mass is immersed in H 2 O with the addition of air and substances called flotation reagents. Hence the name of the process itself - flotation. They combine iron particles with air bubbles and raise them to the surface in a foamy form. Waste rocks settle to the bottom.

magnetic separation. The most common method, based on the difference in the effects of magnetism on various components of the ore mass. Separation can be carried out in the case of wet and dry rocks. In the course of processing, drum mechanisms equipped with powerful electromagnetic elements are used.

Gravity cleaning. For its implementation, special suspensions with a density below the density of iron and above the density of barren rocks are used. The natural forces of gravity push the side components up, and the suspension absorbs the iron particles and leaves them at the bottom.

Flushing. It is used to remove sand and clay from the extracted materials - to separate them, it is enough to use a water jet under high pressure. The process takes place under high pressure and provides up to 5% enrichment. This is a relatively small indicator, because this method is always used in conjunction with other methods.

Iron ores are called rocks containing iron, the extraction of iron from which is economically feasible. There are a lot of minerals containing iron, but in most cases either the iron content in them is small, or the mineral itself is found in nature in small quantities.
Having highest value minerals containing iron can be divided into the following four groups depending on their chemical composition: 1) iron oxides; 2) iron carbonate; 3) siliceous iron; and 4) sulphurous iron compounds. The names and list of these minerals are presented in Table. 7.

Magnetite. The chemical formula of magnetite (magnetic iron ore) is Fe3O4. It contains 72.4% Fe and 27.6% O2. Its color is dark, from gray to black; the mineral has magnetic properties. The syngony is cubic, the type of symmetry is hexaoctahedral, the hardness is 5.5-6; beats weight 4.9-5.2. The share of this mineral in the total production of iron ores is small. However, in some metallurgical regions, for example, in the Urals or in Sweden, magnetite ores are predominant.
Under natural conditions, magnetite, while retaining its crystalline structure, is oxidized to one degree or another. The oxygen content in the magnetic iron ore in this case no longer fully corresponds to the formula Fe3O4 or FeO*Fe2O3.
Usually, in ores formed by magnetic iron ore, in addition to magnetite, there are products of its weathering - semi-martite and martite. According to the classification adopted by Acad. M.A. Pavlov. magnetic iron ore includes such ores in which the Fetot/FeO ratio is less than 3.5 (instead of 2.333 in unoxidized magnetic iron ore). Ores with a Fetot/FeO ratio of more than 3.5 and less than 7 are classified as semi-martites, and, finally, ores with a Fetot/FeO ratio of more than 7 are classified as martites. Sokolov, accepting the same figures, instead of the Fetot/FeO ratio, used the Fetot/FeFeO ratio. Thus, the above classification of magnetite ores is conditional.
Hematite. Chemically pure iron oxide contains 70% Fe and 30°/o O2. In nature, two polymorphic modifications of iron oxide are known - stable a-Fe2O3 (trigonal oingony) and unstable y-Fe2O3 (cubic system), which has strong magnetic properties and is called maghemite.
Hematite is represented by the first modification. The color of crystalline varieties of hematite is iron-black to steel-gray. Specific gravity of hematite is 5.0-5.3, hardness is 5.5-6. Hematite forms the basis of the world's most important iron ore deposits. Associated with rocks of various geological periods, these ores are widely distributed in a variety of forms. Many of these species are named after their distinctive features; such as red ironstone, oolitic red ironstone, ferruginous mica, red glass head, etc.
Brown ironstones. For a long time it was believed that iron oxide forms the following chemical compounds with water: turite - 2Fe2O3*H2O (66.31% Fe and 5.3% water of hydration); goethite - Fe2O3*H2O (62.92% Fe and 10.1% water of hydration); limonite - 2Fe2O3 * 3H2O (59.88% Fe and 14.43% water of hydration); xythoonderite-Fe2O3*2H2O (57.14% Fe and 18.36% hydrate mode); limnite - Fe2O3 * 3H2O (52.3% Fe and "25.3% water of hydration).
AT recent times As a result of X-ray studies, it was found that in fact, iron oxide forms with water one chemical compound with a ratio of Fe2O3:H2O = 1:1, which has a certain crystal lattice. Increasingly water-rich varieties of iron hydroxides are essentially hydrogels, and not compounds of a certain composition. They usually contain adsorbed water in varying amounts.
In modern textbooks on mineralogy, the goethite formula is often depicted as HFeO2 (given that Fe in goethite is associated with hydroxyl), and the limonite formula (all iron hydroxides for which Fe2O3:H2O> 1) is HFeO2*aq (aqua in Latin is water ). Tourite, according to x-ray and thermal studies, turned out to be a mixture of goethite and limonite with hydrohematite and, therefore, is not an independent mineral.
The system of goethite is rhombic, rhombo-pyramidal type of symmetry.
The color of limonite and goethite is dark brown to black. Hardness of goethite 4.5-5.5, limonite 4-1; specific gravity goethite 4.0-4.4, limonite - ranges from 3.3 to 4.0.
By physical condition and appearance There are many varieties of brown iron ore: brown glass head, ordinary brown iron ore, marsh and lake ores, and others.
Carbonates. The most important representative of this group is the mineral called siderite, iron spar or feldspar; its composition is determined by the formula FeCO3 (48.3% Fe and 37.9% CO2). Of the isomorphic impurities, manganese and magnesium carbonates are most often present. Syngony of siderite is trigonal. The color of siderite in its fresh state is yellowish-white, grayish, sometimes with a green or brownish tint. The hardness of siderite is 3.5-4.5; specific gravity 3.9.
During weathering, siderite oxidizes to form limonite and goethite.
iron silicates. Iron silicates are included as impurities in some iron ores. Many minerals are classified as iron silicates, for example, a group of chlorites, one of the representatives of which is chamosite (approximate formula 4FeO*Al2O3*3SiO2*4H2O). The content of FeO in this silicate ranges from 34.3 to 42.5%.
Of the minerals of other groups containing iron silicates, one should name nontronite, the composition of which is determined by the formula: m (Mg3 [OH] 2) p ((Fe, Al) 2 2) nH2O, almandine - Fe3Al23; and andradite Ca3Fe23.
Sulfur compounds of iron. One of the minerals representing this group is pyrite (sulphurous pyrites, iron pyrites) FeS2, containing 46.7% Fe and 53.4% ​​S. Due to the high sulfur content, minerals containing iron sulfides are not used as iron ores. Pyrite or pyrite ores are mined in significant quantities for the production of sulfuric acid, while the ores are roasted in air. During roasting, most of the sulfur is removed, the solid residue is mainly iron oxide and is called pyrite cinders. These cinders after agglomeration can go to the blast furnace.
Marcasite is a polymorphic variety of FeS2 and has a rhombic system (pyrite has a cubic system).

The most important geochemical feature of iron is the presence of several oxidation states. Iron in a neutral form - metallic - composes the core of the earth, possibly present in the mantle and very rarely found in the earth's crust. Ferrous iron FeO is the main form of iron in the mantle and the earth's crust. Oxide iron Fe2O3 is characteristic of the uppermost, most oxidized, parts of the earth's crust, in particular, sedimentary rocks.

In terms of crystal chemical properties, the Fe2+ ion is close to the Mg2+ and Ca2+ ions, other main elements that make up a significant part of all terrestrial rocks. Due to their crystal chemical similarity, iron replaces magnesium and, in part, calcium in many silicates. The content of iron in minerals of variable composition usually increases with decreasing temperature.

iron minerals

In the earth's crust, iron is widely distributed - it accounts for about 4.1% of the mass of the earth's crust (4th place among all elements, 2nd among metals). In the mantle and the earth's crust, iron is concentrated mainly in silicates, while its content is significant in basic and ultrabasic rocks, and low in acidic and intermediate rocks.

A large number of ores and minerals containing iron are known. Ores are natural minerals containing iron in such quantities and compounds, in which the industrial extraction of the metal from them is economically feasible. The iron content in industrial ores varies widely - from 16 to 70%. Depending on the chemical composition, iron ores are used for iron smelting in their natural form or, if they contain less than 50% Fe, after enrichment. Most of the iron ores are used to smelt iron, steel, and ferroalloys. In relatively small quantities, they are used as natural paints (ochre) and weighting agents for drilling muds.

Of the greatest practical importance are red iron ore (hematite, Fe2O3; contains up to 70% Fe), magnetic iron ore (magnetite, FeO.Fe2O3, Fe3O4; contains 72.4% Fe), brown iron ore or limonite (goethite and hydrogoethite and hydrogoethite, respectively FeOOH and FeOOH nH2O). Goethite and hydrogoethite are most often found in the weathering crust, forming the so-called "iron hats", whose thickness reaches several hundred meters. They can also be of sedimentary origin, falling out of colloidal solutions in lakes or coastal areas of the seas. In this case, oolitic, or legume, iron ores are formed. They often contain vivianite Fe(3PO4)2 8H2O, which has the form of black elongated crystals and radially radiant aggregates.

In nature, iron sulfides are also widespread - pyrite FeS2 (sulfur or iron pyrite) and pyrrhotite. They are not iron ore - pyrite is used to produce sulfuric acid, and pyrrhotite often contains nickel and cobalt.

Other common iron minerals are:

· Siderite - FeCO3 - contains approximately 35% iron. It has a yellowish-white (with a gray or brown tint in case of contamination) color.

· Marcasite - FeS2 - contains 46.6% iron. It occurs in the form of yellow, like brass, bipyramidal rhombic crystals.

Lollingite - FeAs2 - contains 27.2% iron and occurs as silvery-white bipyramidal rhombic crystals.

· Mispikel - FeAsS - contains 34.3% iron. Occurs as white monoclinic prisms.

Melanterite - FeSO4 7H2O - is less common in nature and is a green (or gray due to impurities) monoclinic crystals with a vitreous luster, fragile.

· Vivianite - Fe3 (PO4) 2 8H2O - occurs in the form of blue-gray or green-gray monoclinic crystals.

The earth's crust also contains other, less common iron minerals, for example.