What is chalk? Properties, extraction, application and price of chalk. calcium carbonate in nature

Well, I hope everyone guessed that we are talking about a substance, one of the modifications of which is known to us as "chalk", and this issue is dedicated to the upcoming beginning of the school year - although all sorts of innovations are now coming to schools like whiteboards with markers or even interactive whiteboards , dark board - black, brown or green and chalk are still the main attributes of the educational process.

Even if someone, after graduating from school, stops his contact with educational authorities once and for all, his hands do not stop touching the closest relative of chalk - every time we pick up an egg to peel it from the shell, we touch limestone - a form of carbonate hardening calcium eggshell and shellfish shells.

... and Carrara marble would not look after you ...

So, today's remarkable substance is the many-sided potassium carbonate, which exists (and is known) in the form various forms. The formula of this compound is CaCO 3 , it is a salt in which the calcium cation is ionically bonded to the carbonate anion. This substance is quite common in nature, as the only substance it forms two minerals - calcite and aragonite, and is also the main component of such minerals as limestone, chalk and marble. The composition of the last trinity, in addition to calcium carbonate, includes its "cousin" - magnesium carbonate MgCO 3, as well as metal oxides; it is the oxides of transition metals that give marble its characteristic color - ferric oxide gives shades of red, and trivalent chromium oxide gives shades of green.

Old drawing, relevant in connection with the introduction this year in 4th grade course "Fundamentals of Religious Culture and Secular Ethics"

As for school crayons, the times when they consisted of almost pure chalk have sunk into oblivion. It is guaranteed that in my school childhood we wrote with almost pure chalk, in which pieces of shells sometimes came across (why this is a sign of pure chalk - it will be literally in the next paragraph), and we loved to test the nerves of teachers, specially drawing such a piece of shell across the board (well and this topic, perhaps, I will not develop). Modern molded school chalk is 40% chalk itself (calcium carbonate) and 60% gypsum (this is another relative of our today's "hero" - calcium sulfate dihydrate - CaSO 4 ˙H 2 O), but the addition to it pigments - organic or inorganic origin allows you to diversify White color school chalk, giving it a color.

Chalk cliffs on the south coast of England near the cities of Seaford and Eastbourne

Most of the currently known rocks containing calcium carbonate are of sedimentary origin - they were formed from the shells and skeletons of dead sea inhabitants, compacted as a result of pressure from the next layer sedimentary rocks. Chalk and limestone are similar materials, the difference is that chalk is less compact and therefore softer. The formation of marble, calcite and aragonite requires more time - the initial substance for the formation of marble is limestone or chalk, which, under the influence of high pressures and temperatures - the conditions common for the geological formation of minerals, are rebuilt into a form with a more compact and dense crystal lattice.

Bio- (more precisely - zoogenic) deposits of calcium carbonate gave the name to the whole geological period- Cretaceous period (miles of Mel). This period is the last period of the Mesozoic era, it lasted 80 million years, began 145 million years ago, ended 65 million years and is best known for the "Cretaceous catastrophe", which resulted in a mass extinction of species - many gymnosperms, aquatic reptiles, pterosaurs, all dinosaurs (but the birds survived). Ammonites disappeared, many brachiopods, almost all belemnites. In the surviving groups, 30-50% of the species became extinct.

One interesting form of calcium carbonate minerals is the transparent calcite or Icelandic spar. In 1669 the Danish naturalist Rasmus Bartholin at work Experimentia Crystalli Islandici Disdiaclastici described the strange property of Icelandic spar, now known as "double refraction". It lies in the fact that if a beam of light falls perpendicular to the surface of the crystal, then on this surface it splits into two beams. The first beam continues to propagate straight, and is called ordinary, while the second one deviates to the side, violating the usual law of refraction of light, and is called extraordinary, and, accordingly, looking through a calcite crystal, we see a “doubled” image.

Birefringence in Icelandic spar crystals has been used and is being used in practice, for example, for rangefinders in bombsights, however, it is natural that the use of calcium carbonate by mankind began a very long time ago.

Thus, one of the first examples landscape design"can be considered prehistoric white horses of the British county of Wilshire, which were obtained by removing the turf and fertile layer soil, exposing the underlying layer of chalk.

Calcium carbonate in the form of limestone and marble has been used since ancient times as a building material. Despite a certain softness of limestone, mankind did not refuse them. practical application- so the great pyramid of Giza, four millennia remained the most tall building in the world, built from about two and a half million blocks of limestone.

Again, since antiquity, calcium carbonate has given rise to another construction material, however, this required the first chemical production. Since the time of Ancient Egypt, architects have known that calcining carbonate makes it possible to obtain slaked (or calcined) lime, the main component of which is calcium oxide CaO. Not slaked lime used in binders mortars and in the manufacture of cement - by itself or after treatment with water (slaked lime or calcium hydroxide Ca (OH) 2). There are known cases of the use of quicklime in the defense of castles - quicklime actively interacts with water, and since the skin of a healthy person is always wet (especially if this healthy man creeps along the siege ladder to someone else's fortress wall) the besieged poured out on the besiegers quicklime causing burns to their skin and organs of vision.

Also, since ancient times, calcium carbonate has been used to reduce the acidity of the soil (this is also the same recipe for an amateur gardener, of which there were millions in the country of councils - throw into the soil, on which the moss began to “ear”, egg shells- moss grows on acidic soils, and calcium carbonate, being a salt of a weak acid, reacts with the free acid of the soil, binding it).

Since the beginning of the twentieth century, calcium carbonate has been used in many industrial productions in addition to the construction industry, for example - pulp and paper for the production of high-quality coated paper. Calcium carbonate is used as a filler for added strength polymer materials, it was used in bakery production (to increase calcium intake). Today, calcium carbonate is used in Food Industry as white food coloring (E170). Calcium carbonate has been and is used in tooth powders and toothpastes, although for this purpose it is not "organic" chalk formed from the remains of extinct animal species that is used, but synthetic - for oral hygiene, calcium carbonate is obtained by passing carbon dioxide through slaked lime: Ca ( OH) 2 + CO 2 = CaCO 3 + H 2 O. Why so - I don’t specifically explain, think for yourself, activating your brain by the beginning of the school year, but I suggest that the cause of this phenomenon can be found by carefully reading the post ( throw guesses in the comments, rights, I won’t screen them).

Unfortunately, the fact that calcium carbonate reacts with acids has now become a whole problem for the preservation of architectural and artistic heritage - buildings and sculptures and various forms of calcium carbonate - especially from less dense limestone, although marble is also a problem, although it is destroyed. at a slower rate, are damaged due to acid erosion caused by acid rain.

So, we can say that no substance has made such a contribution to the culture of mankind and continues to make it to this day, like calcium carbonate. We can trace his path in human civilization from the first rock paintings on the walls of the cave with chalk, the pyramids to school board and chalk and glass and concrete buildings. And, knowing how human civilization owes calcium carbonate, we will not be mistaken if we say that human civilization grew up on bones - bones huge amount organisms that became extinct at the end of the Cretaceous.

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Limestone is very known material which is used different areas folk industry. One of its brightest representatives is ordinary chalk, used to produce quicklime.

There are also other types of this breed, which are much stronger, which makes it possible to make facing tiles from them. Such material is in great demand in the construction world, so it has unique decorative characteristics.

When choosing such products, the price of limestone tiles may vary depending on its quality.

Composition of limestones

This rock was formed by the layering of organic calcium remains of living beings. Limestone, in its bulk, consists of several types of minerals:

1. Calcite is a part of all types of rocks. Its mass fraction in pure limestone can reach more than 90%.

2. Clay minerals.

3. Dolomite.

4. Quartz.

5. Gypsum (very rarely may be present in the composition).

6. Organic remains and many others.

The exact composition of such a substance depends specifically on the conditions of the environment in which it was formed. For example, if we talk about dolomitic limestone, then it contains magnesium oxide (MgO), the percentage of which can reach 17%, and in marl limestone, on the contrary, there is a ratio of SiO2 + R3O3 in an amount from 6% to 21%.

Limestones are often named according to the predominant substance in the composition. So, sandy rocks contain quartz, opal and chalcedony.

Main characteristics

Limestones have a certain color scheme. The main color is considered white with shades of gray and yellow. There are also rocks that have a brown or reddish color, which indicates the presence of iron and manganese in its composition.

If algae also took part in the formation of limestone, then they can color it greenish. There is also black material, but these types of rocks are very rare.

The density of this rock also varies and for each type of substance it can differ significantly.

Limestone is used to make various kinds slabs for cladding, as well as it is used for the construction of roads and other coatings. Sometimes it is used as filters for installation on special hydraulic structures.

Limestone is a unique substance that has different properties which makes it very popular in various fields.

What limestone consists of, the video tells in detail:

Chalk, marble and limestone, from a chemical point of view, are the same substance - calcium carbonate, or rather, one of its crystalline modifications - calcite.

Chalkis a soft rock that is easy to grind into powder. Chalk is used as a white pigment in the paint and varnish and rubber industries, in the production of Portland cement, as a writing material.

Limestonehas greater hardness: it has long been used as a material for stone structures. Most of the temples of grand-ducal Moscow were built from Myachkovo limestone, which was mined near the village of Myachkovo on the Moskva River and delivered to the construction site on special ships. No wonder Moscow in the old days was called white-stone. Currently, limestone is a valuable material in the production of cement, in metallurgy as a flux (flux in metallurgy is a substance introduced into the charge to bind impurities, for example P 2 O 5, SiO2 , in fusible slags,) and in the chemical industry in the production of soda, bleach, calcium carbide.

Chalk and limestone are sedimentary rocks formed from the remains of the shells of living organisms (primarily the ancient protozoa - radiolarians and foraminifers).

Assumption Cathedral on Gorodok. Zvenigorod. Around 1399

White-stone carving of the Assumption Cathedral on Gorodok.

Marble- a metamorphic rock formed during recrystallization under pressure of sedimentary carbonate rocks - mainly limestones. It also consists of calcite (calcium carbonate), however, unlike chalk and limestone, it is a coarse-grained material: on a chip

a piece of marble, its granular structure is clearly visible. Compared to chalk and limestone, marble is hard: it was not for nothing that the ancients built temples from it. Thanks to various impurities, marble is often colored, the marble of some deposits has a beautiful structure in which layers of different colors alternate. In ancient times, snow-white Carrara marble, pink Parian, yellow Sienese. The main temple of the Athenian Acropolis - the famous Parthenon is built of blocks Pentelic marble, which was mined in the town of Pentelikon, northeast of Athens. Pentelian marble has a subtle golden hue, which intensifies when you look at the Parthenon in the evening, at sunset. In Italy, a common type of marble is chippolino- so called white marble with small yellow or green veins. And here is the famous red Veronese marble ( Rosso di Verona ) is actually a brown-red limestone in which fossils are often found.

CaO- calcium oxide or quicklime, it is obtained by decomposition of limestone: CaCO 3 \u003d CaO + CO 2 is an oxide of an alkaline earth metal, therefore it actively interacts with water: CaO + H 2 O \u003d Ca (OH) 2

Ca(OH) 2 - calcium hydroxide or slaked lime, so the reaction CaO + H 2 O \u003d Ca (OH) 2 is called lime slaking. If the solution is filtered, lime water is obtained - this is an alkali solution, so it changes the color of phenolphthalein to crimson.

Hydrated lime is widely used in construction. Its mixture with sand and water is a good binding material. Under the action of carbon dioxide, the mixture hardens Ca (OH) 2 + CO 2 \u003d CaCO3 + H 2 O.

At the same time, part of the sand and the mixture turns into silicate Ca (OH) 2 + SiO 2 \u003d CaSiO 3 + H 2 O.

The equations Ca (OH) 2 + CO 2 \u003d CaCO 2 + H 2 O and CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2 play an important role in nature and in shaping the appearance of our planet. Carbon dioxide in the form of a sculptor and architect creates underground palaces in the strata of carbonate rocks. It is capable of moving hundreds and thousands of tons of limestone underground. Through cracks in rocks, water containing carbon dioxide dissolved in it enters the limestone thickness, forming cavities - castra caves. Calcium bicarbonate exists only in solution. ground water move in the earth's crust, evaporating water under suitable conditions: Ca (HCO3) 2 \u003d CaCO3 + H 2 O + CO 2 , this is how stalactites and stalagmites are formed, the formation scheme of which was proposed by the famous geochemist A.E. Fersman. There are a lot of castra caves in the Crimea. Science studies them speleology.

Used in construction calcium carbonate CaCO3- this is chalk, limestone, marble. All of you have seen our railway station: it is finished with white marble brought from abroad.

an experience: blow through a tube into a solution of lime water, it becomes cloudy .

Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O

Rides to the formed sediment acetic acid, effervescence is observed, because carbon dioxide is released.

CaCO 3 +2CH 3 COOH \u003d Ca (CH 3 SOO) 2 +H 2 O + CO 2

THE TALE ABOUT THE CARBONATE BROTHERS.

Three brothers live on earth
From the Carbonate family.
The older brother is a handsome MARBLE,
Glorious in the name of Karara,
Excellent architect. He
He built Rome and the Parthenon.
Everyone knows LIMESTONE,
That's why it's named like that.
Famous for his work
Building a house behind the house.
Both able and able
The younger soft brother MEL.
How to draw, look
This CaCO 3!
Brothers love to frolic
Burn in a hot oven
CaO and CO 2 are then formed.
It's carbon dioxide
Each of you is familiar with him,
We breathe it out.
Well, this is Sao -
Hot burnt quicklime.
Add water to it
Thoroughly mixing
To avoid trouble
We protect our hands
Cool mixed LIME, but SLAKED!
milk of lime
The walls are whitewashed easily.
The bright house cheered up
Turning lime into chalk.
Hocus pocus for the people:
One has only to blow through the water,
How easy it is
Turned into milk!
Now it's pretty smart.
I get soda
Milk plus vinegar. Ay!
Foam is pouring over the edge!
All in worries, all in work
From dawn to dawn -
These brothers the Carbonates,
These CaCO 3!

Repetition: CaO– calcium oxide, quicklime;
Ca(OH) 2 - calcium hydroxide (slaked lime, lime water, milk of lime, depending on the concentration of the solution).
General is the same chemical formula Ca(OH) 2 . Difference: lime water is a transparent saturated solution of Ca (OH) 2, and milk of lime is a white suspension of Ca (OH) 2 in water.
CaCl 2 - calcium chloride, calcium chloride;
CaCO 3 - calcium carbonate, chalk, shell rock marble, limestone.
L/R: collections. Next, we demonstrate the collection of minerals available in the school laboratory: limestone, chalk, marble, shell rock.
CaS0 4 ∙ 2H 2 0 - hydrated calcium sulfate, gypsum;
CaCO 3 - calcite, calcium carbonate is part of many minerals that cover 30 million km 2 on earth.

The most important of these minerals is limestone. Shell rocks, limestones of organic origin. It goes to the production of cement, calcium carbide, soda, all kinds of lime, in metallurgy. Limestone is the backbone of the construction industry and many building materials are made from it.

Chalk it's not just tooth powder and school chalk. It is also a valuable additive in the production of paper (coated - the highest quality) and rubber; in the construction and repair of buildings - as a whitewash.

Marble is a dense crystalline rock. There is color - white, but most often various impurities color it in different colors. Pure white marble is rare and is mainly used by sculptors (statues of Michelangelo, Rodin. In construction, colored marble is used as facing material(Moscow metro) or even as the main building material of palaces (Taj Mahal).

In the world of interesting "MAUSOLEUM" Taj Mahal ""

Shah Jahan from the Mughal dynasty held in fear and obedience almost all of Asia. In 1629, Mumzat Mahal, Shah Jahan's beloved wife, died at the age of 39 during childbirth on a campaign (it was their 14th child, all of them boys). She was unusually beautiful, bright, intelligent, the emperor obeyed her in everything. Before her death, she asked her husband to build a tomb, take care of the children, and not marry. The saddened king sent his messengers to all big cities, the capitals of neighboring states - to Bukhara, Samarkand, Baghdad, Damascus, to find and invite the best craftsmen- in memory of his wife, the king decided to build the best building in the world. At the same time, messengers sent to Agra (India) plans for all the best buildings in Asia and the best building materials. They even brought malachite from Russia and the Urals. The chief masons came from Delhi and Kandahar; architects - from Istanbul, Samarkand; decorators - from Bukhara; gardeners from Bengal; the artists are from Damascus and Baghdad, and the well-known master Ustad-Isa was in charge.

Together, over 25 years, a melomarble structure was built, surrounded by green gardens, blue fountains and a red sandstone mosque. 20,000 slaves erected this miracle of 75 m (with a 25-storey building). Nearby, he wanted to build a second mausoleum of black marble for himself, but did not have time. He was overthrown from the throne by his own son (2nd, and he also killed all his brothers).

The ruler and ruler of Agra spent the last years of his life looking out of the narrow window of his dungeon. 7 years so the father admired his creation. When his father went blind, his son made him a system of mirrors so that his father could admire the mausoleum. He was buried in the Taj Mahal, next to his Mumtaz.

Those entering the mausoleum see cenotaphs - false tombs. The places of eternal rest of the great khan and his wife are downstairs, in the basement. It's all in there precious stones, which glow as if alive, and the branches of fabulous trees, intertwined with flowers, adorn the walls of the tomb with intricate patterns. Turquoise-blue lapis lazuli, green-black nephrites and red amethysts processed by the best carvers sing the love of Shah Jahal and Mumzat Mahal.

Every day tourists rush to Agra who want to see the true wonder of the world mausoleum Taj Mahal, as if hovering above the ground.

CaCO 3 - this is the building material of the external skeleton of mollusks, corals, shells, etc., egg shells. (illustrations or Animals of the coral biocenosis” and display of a collection of sea corals, sponges, shell rock).

calcium carbonate

Calcium carbonate CaCO 3 is one of the most common compounds on Earth. Minerals based on CaCO 3 cover about 40 million km 2 of the earth's surface. Chalk, marble, limestone, shell rock - all this is CaCO 3 with minor impurities, and calcite is pure CaCO 3.

The most important of these minerals is limestone. (It is more correct to speak not about limestone, but about limestones: limestones of different deposits differ in density, composition and amount of impurities.) Limestones are found almost everywhere. In the European part of the USSR, limestones are found in deposits of almost all geological ages. Shell rocks - limestones of organic origin - are especially common on the northern coast of the Black Sea. The famous Odessa catacombs are former quarries where shell rock was mined. The western slopes of the Urals are mainly composed of limestones.

In its pure form, limestone is white or light yellow, but impurities give them a darker color.

The purest CaCO3 forms transparent crystals of calcareous or Icelandic spar, which is widely used in optics. And ordinary limestones are used very widely - in almost all sectors of the national economy.

Most limestone goes to the needs chemical industry. It is indispensable in the production of cement, calcium carbide, soda, all types of lime (slaked, quicklime, chlorine), bleaching solutions, calcium cyanamide, lime water and many other useful substances.

Metallurgy also consumes a significant amount of limestone - as fluxes.

No building is complete without limestone. Firstly, they build from it, and secondly, many building materials are made from limestone.

Limestone (crushed stone) strengthens roads, limestone (in powder form) reduces soil acidity. In the sugar industry, limestone is used to refine sugar beet juice.

Another type of calcium carbonate is chalk. Chalk is not only tooth powder and school crayons. It is used in the paper and rubber industry - as a filler, in construction and in the repair of buildings - for whitewashing.

The third variety of calcium carbonate, marble, is less common. It is believed that marble was formed from limestone in ancient geological epochs. With displacements earth's crust separate deposits of limestone turned out to be buried under layers of other rocks. Under the influence high pressure and temperature, the process of recrystallization took place there, and the limestone turned into a denser crystalline rock - marble.

The natural color of marble is white, but most often various impurities color it in a variety of colors. Pure white marble is not common and goes mainly to the workshops of sculptors. Less valuable varieties of white marble are used to make switchboards and panels in electrical engineering. In construction, marble (of all colors and shades) is used not so much as a structural material, but as a facing material.

And, to put an end to calcium carbonate, a few words about dolomite, an important refractory material and raw material for cement production.

This is a double magnesium-calcium salt of carbonic acid, its composition is CaCO 3 MgCO 3.

Calcium sulfate CaSO 4 is also widely distributed in nature. The well-known mineral gypsum is CaSO 4 2H 2 O crystalline hydrate. How gypsum binder have been used for many centuries, almost since the time of the Egyptian pyramids. But natural gypsum (gypsum stone) is not characterized by the ability to harden in air and at the same time hold stones together.

Gypsum acquires this property during firing.

If natural gypsum is calcined at a temperature not exceeding 180°C, it loses three-quarters of the water associated with it. It turns out a crystalline hydrate of the composition CaSO 4 0.5H 2 O. This is alabaster, or burnt gypsum, which is used in construction. In addition to the astringent properties, burnt gypsum has one more thing. useful property. Hardening, it slightly increases in volume. This allows you to get good casts from plaster. During the hardening of burnt gypsum mixed with water (gypsum dough), one and a half water molecules lost during firing are added, and again a gypsum stone CaSO 4 2H 2 O is obtained.

If firing gypsum stone lead at temperatures above 500 ° C, anhydrous calcium sulfate is obtained - "dead gypsum". It cannot be used as an astringent.

You can "revive" dead gypsum. To do this, it is necessary to calcinate it at even higher temperatures - 900 ... 1200 ° C. A so-called hydraulic gypsum is formed, which, being mixed with water, again gives a hardening mass, very durable and resistant to external influences.

The calcium salt of phosphoric acid is the main component of phosphorites and apatites. These minerals (also quite common) are raw materials for the production of phosphate fertilizers and some other chemical products. Since the most useful part of phosphorites and apatites is not calcium, but phosphorus, we will not talk about them in detail, referring the reader to the article about element No. 15. Let us only mention that calcium salts of phosphoric acids, primarily Ca 3 (PO 4) 2 tricalcium phosphate, are always present in human and animal organisms. Ca 3 (PO 4) 2 is the main "structural material" of our bones.

This calcium salt is much rarer in nature than calcium carbonate, sulfate or phosphate. It is obtained as a by-product in the production of soda by the ammonia method. Natural calcium chloride is usually CaCl 2 6H 2 O crystalline hydrate, which, when heated, first loses four water molecules, and then the rest.

Anhydrous calcium chloride is highly hygroscopic and is used to dry liquids and gases.

Calcium chloride is highly soluble in water. If you pour such a solution on a dirt or gravel road, it will remain wet much longer than after watering. This is because the vapor pressure over the calcium chloride solution is very low; such a solution absorbs moisture from the air and therefore does not dry out for a long time.

Another application of this salt is related to the low freezing points of calcium chloride solutions. These solutions are used in refrigeration systems. And mixtures of this salt with snow or finely crushed ice melt at temperatures well below zero. The melting point of the refrigeration mixture of 58.8% CaCl 2 · 6H 2 O and 41.2% snow is minus 55°C.

Calcium chloride is widely used in medicine. In particular, intravenous injections of CaCl 2 solutions relieve spasms of the cardiovascular system, improve blood clotting, and help fight swelling, inflammation, and allergies. Doctors prescribe solutions of calcium chloride not only intravenously, but simply as an internal medicine. Calcium chloride has also become one of the components of vitamin B 15 .

Unlike CaCl 2 and other calcium halides, this salt is practically insoluble in water. Calcium fluoride is part of apatite, where it is a useless impurity. But pure crystalline calcium difluoride is a very useful substance. This is one of the main metallurgical fluxes - substances that help separate metals from gangue. In this capacity, calcium fluoride has been used for a very long time, and it is no coincidence that one of the names of this mineral is fluorspar. Fluvikovy - from "melt".

Sometimes in nature there are large, weighing up to 20 kg, absolutely transparent crystals of this salt. They have another mineralogical name - fluorite. Such crystals are extremely valuable for optics, because they transmit ultraviolet and infrared rays much better than glass, quartz or water. The demand for fluorite crystals far exceeds the reserves of explored deposits, and it is no coincidence that fluorite began to be produced artificially on an industrial scale.