What is chalk and what does it consist of. What is chalk? What is the difference between chalk

Who among us does not know chalk? Whose pockets and fingers were not soiled by a piece of light stone the color of snow in childhood? Who does not know the happiness of the artistic creation of the "Cretaceous" period? Who, as a teenager, did not investigate the properties of chalk in "bubble" experiments, did not examine a chalk smear under a microscope?

Mineral chalk is a witness to eras that have passed tens of millions of years ago. Awareness of this fact changes the perception of familiar material. Having a biological origin, the chalk stone learned its properties from organisms that lived in ancient times.

Origin of chalk

The Cretaceous period is a period of time covering about 80 million years during the reign of dinosaurs. Warm and shallow (30-500 meters deep) seas of that time gave shelter to myriads of the smallest mollusks that built their skeletons and shells from calcium extracted from the water.

The remains of these creatures, accumulated in bottom sediments in multi-meter layers, turned into the well-known chalk. In percentage terms, the mineral chalk is divided into the following parts:

• fragments of skeletons - about 10%. We are talking not only about the simplest creatures, but also about multicellular animals endowed with the ability to extract and concentrate calcium salts in tissues.

• shells of microscopic mollusks foraminifera - about 10%. However, not all rhizopods (the Russian name for animals) had a calcareous shell. Some built their protective layer from a chitin-like substance. In many ways, therefore, in the Cretaceous deposits of calcium carbonate itself, no more than 98% (and no less than 91%) are found.

• fragments of calcareous growths of algae - up to 40%. Coccolithophores - the plant plankton of the oceans - feel great in our time. Up to 98% of the microscopic living suspension in the upper layers of the seas accounted for this type of algae. Therefore, the calcareous mineral, in fact, is a product for the most part of plant rather than animal origin. The origin of chalk is the merit of plants!

• finely dispersed crystalline calcite - up to 50%. We are talking about "fragments of debris", and so miniature in size that it is not possible to determine their biological affiliation.

• insoluble minerals (mainly silicates) - up to 3%. This is mainly geological debris (sand and fragments of various rocks) brought into the Cretaceous deposits by winds and currents. Although, in addition, biogenic calcium formations are enriched with phosphorus and silicon compounds during metabolic processes during the life of the animal.

Shells of more or less large mollusks, skeletons of coelenterates, concretions of alien minerals are relatively rare in the Cretaceous strata. Only a few photographs of chalk show the observer arrays dotted with cavities of bulk shells.

Chalk composition

It is conditionally considered that the chemical formula of chalk corresponds to the formula of calcium carbonate CaCO3. However, the real composition of chalk differs from the composition of the calcium salt of carbonic acid.

Actually, calcium oxide in the mineral is about half: the concentration of CaO ranges from 47% to 55%. There is also a lot of carbon dioxide in the chalk, which is in a bound state. CO2 - up to 43%!

Magnesium oxide MgO can reach up to 2% of the total mass of chalk. Inclusions of quartz SiO2 are usually not too significant, but in general are mandatory, and can reach a concentration of 6%. The density of chalk with a high silicon content is greater than normal.

Somewhat less in the composition of chalk aluminum oxide Al2O3 - no more than 4%. A variety of iron oxides rarely exceed the half-percent concentration threshold, but it is they that color the chalk red quite often.

Chalk application

As an independent building material, chalk is used only as a raw material for the production of chalk paints. Out of mass use half a century ago, the whitewashing of rooms with a colloidal solution of pure or colored chalk is almost never done today.

As a masonry stone, chalk is untenable - although the premises dug into the chalk massifs remain habitable for centuries. The low hardness of the chalk makes it possible to gradually excavate the stone without large-scale destruction of the massif.

In the construction industry, the use of chalk is growing and expanding. Production of cement and glass without chalk is almost impossible! Chalk is required for paper-making enterprises, light industry, and organic chemistry. Paints and rubber, hygiene products and soil fertilizers, animal feed and perfume compositions are produced using chalk.

Can you eat chalk?

It is known that with a lack of calcium in the body, a craving for eating chalk can develop. The experience of generations that grew up in conditions of organic calcium deficiency says: chalk is edible! However, doctors, answering the question whether it is possible to eat chalk, are not so unambiguous.

The properties of chalk change dramatically under the influence of gastric juice. Chalk, which has passed through the crucible of oxidative processes, loses its original neutrality and becomes a chemically active reagent. In terms of effectiveness, it is made similar to slaked lime. The mucous membrane of the digestive tract suffers from contact with oxidized chalk.

In addition, the concentration of calcium in the chalk is excessively high. Eating chalk can provoke liming of blood vessels. It is much safer to pay attention to medical preparations of this metal in case of calcium deficiency. A tablet of calcium gluconate affects the body much more positively than a piece of eaten chalk.

Stationery, construction and even fodder agricultural chalk are not suitable for human consumption! A person does not have the opportunity to safely (and even more so for his own benefit) process and assimilate this mineral!

Cretaceous deposits of Eurasia stretched in a wide strip from the Kazakh river Emba to the western tip of Britain. The deposits reach the greatest thickness south of Kharkov: here there are real chalk mountains with a massif thickness of up to 600 m. The ongoing development of the white mineral promises scientists many new discoveries.

Many people know the feeling of an irresistible desire to eat a piece of chalk. And some cannot do without a daily portion of this supplement at all. What caused such a need of the body, and what kind of chalk can be used? Food chalk is ideal for eating, which does not contain harmful substances in its composition and is purified.

What caused the desire to eat chalk?

Such an oddity in taste preferences, like an unexpected desire to eat chalk, most often indicates a malfunction in the body. It should be understood that a piece will not get rid of the true cause of the desire. Experts say that the problem may lie in iron deficiency anemia (anemia). Iron deficiency causes a decrease in hemoglobin. This condition leads to rapid aging of the body.

Calcium deficiency is another reason for eating chalk. Not receiving this microelement in the required quantities, the body begins to give such peculiar “signals”. To normalize the condition, it is necessary to review the daily diet and start taking supplements, for example, food chalk.

Even 10-15 years ago, they wrote on the board with lumpy chalk, which can even be eaten. It was this chalk that many managed to taste. It does not contain any harmful substances in the composition, but it also does not have any special benefits for the body.

Calcium carbonate is the main component of lump chalk. It is used for the production of medicines that make it possible to compensate for the lack of a microelement in the body, improve the condition of hair, nails and bone tissue.

Is it possible to eat chalk during pregnancy?

During the period of bearing a baby, the female body experiences a huge load. Almost every pregnant woman suffers from a deficiency of trace elements and nutrients. Such a problem can be expressed in an irresistible desire to gnaw a piece of chalk. Pregnant women may also like the smell of soap, whitewash.

Experts say that in small amounts of chalk (food) during pregnancy, you can use the expectant mother. However, such a "delicacy" should be chosen carefully. Drawing crayons contain various additives and are completely different in taste from the original. It is better not to eat them.

A piece for a pregnant woman will be a good source of calcium. Before using such an unusual product, it is recommended to consult a doctor. Perhaps the expectant mother will need to undergo an examination to find out the reason for such a desire.

Food chalk: benefits and harms to the body

According to doctors, only pharmaceutical chalk, purified from various harmful inclusions and impurities, is suitable for use. It will bring exceptional benefits to the body: it will strengthen the walls of blood vessels, make up for the deficiency of calcium ions. It is necessary to take such chalk according to the age dosage.

For lovers of chalk, the most delicious is the food, purified product. A few small pieces a day will definitely not cause harm to the body. Although, on the other hand, one should not expect much benefit from this “delicacy”. Food chalk will not affect the lack of nutrients in the body.

Food chalk: application

Most meloids cannot live without their favorite treat and day. Each of them has its own "dose". How much can you use chalk, so as not to harm the body? Experts recommend not to get involved in eating this substance.

For some people, food chalk helps to cope with the increased acidity of the stomach. To do this, it is ground into powder and consumed one teaspoon per day. Some pharmaceutical preparations designed to lower the level of gastric acidity contain calcium carbonate. The substance has antacid properties and can be used for peptic ulcer disease.

Can you give chalk to children?

Unexpected taste preferences can also be observed in children. For parents, this is a kind of signal that the growing body lacks nutrients. If the baby began to eat chalk, you should think about the fact that the child's diet is not balanced. Calcium deficiency during the period of active skeletal growth poses a serious danger to the normal physical development of the child. The trace element is necessary to strengthen muscle and bone tissue, is involved in the formation of strong teeth.

A craving for chalk can develop in a child with low hemoglobin. Iron deficiency is a dangerous disease. The body begins to suffer from a lack of oxygen, which leads to fatigue, dizziness. With such problems, you should definitely contact your pediatrician.

It is not worth denying a child the desire to eat a piece of chalk. However, the safest product should be chosen for this purpose. School chalk or the one intended for drawing is completely unsuitable for use as a dietary supplement.

Pharmaceutical chalk is considered harmless. It is produced in the form of calcium gluconate tablets. The dosage is calculated depending on the age of the baby. Purified chalk (food) can also be given to a child to gnaw. It is rarely found in pharmacies. Most often, such a “delicacy” is purchased through online stores.

Additional measures

Constantly eating chalk (even food) is not an option. To make up for the lack of trace elements in the body, you should adjust the diet. For anemia, it is useful to eat foods fortified with iron. These include:

• liver (pork and beef);
• buckwheat grain;
• pomegranate;
• prunes;
• bananas.

With a strong desire to eat a few pieces of chalk, of course, you can. Only it must be a quality product. It should be remembered that you can only use white chalk (food grade) purified from various harmful substances. A photo of such a product is in our article. Please note: the chalk pieces must have an irregular shape. Sometimes you can find sawn chalk in the form of sticks. On their surface, grooves from sawing with tools are visible.

Chalk is a white powdery substance obtained in most cases by crushing, drying and fine grinding of the original sedimentary rock. Chalk is made up of grains of calcite, better known to everyone as calcium carbonate. Calcium carbonate makes up nearly 99 percent of the total chalk. The composition of chalk also includes the smallest grains of quartz, a mineral companion of calcite. The reserves of chalk on our planet are very significant and they are not yet in danger of depletion.

Chalk is used as a filler in the paint and varnish, rubber, and other industries. The use of chalk for the production of building materials is very important. The most important properties of chalk are its exceptionally white color, fairly high natural dispersion, and low abrasiveness.

Chalk is one of the most common materials used in the production of construction and repair work. With the help of chalk diluted with water, primitive can be carried out. This simple composition and today in some cases finds its application. Whitewashing with chalk is an inexpensive and fairly simple method that allows you to get a smooth, matte finish of snow-white color that hides small surface defects. The chalk used for whitewashing is sold dry. Chalk paste is also on sale. To prepare a whitewash solution, it is diluted with water in a certain proportion. Chalk paste and chalk can be stored without losing their qualities and properties for a very long time. Dry chalk in some cases may contain impurities, as well as unground pieces. For this reason, before preparing a whitewash solution, it is advisable to sift the chalk through a sieve, and after dissolving, strain the prepared solution. Chalk paste or dry whitewash chalk is diluted in warm water and stirred thoroughly enough. Laundry soap or washing powder is added to the resulting solution for additional strength. In order for the whitewash not to acquire a yellowish tint, the solution is tinted with a small amount of blue. Instead of blue, a blue tint for water-based paint is quite suitable. To obtain a more durable chalk coating in the same old-fashioned way, add a little wood glue to the whitewash solution. Whitewashing in this case will no longer be dirty, but it will also be much more difficult to wash it off if necessary.

Scientific and technological progress does not stand still and the whitewashing technologies discussed above are no longer used everywhere, as it was about half a century ago. To date, chalk is part of many ready-to-use paints that are widely used for whitewashing. Chalk is also used as a filler for the production of dry building mixes, various grouts and plasters, plastics, paper, rubber, and cable products.

It is very interesting that one of the main industrial areas of consumption of fine chalk is the production of plastics. Chalk performs a number of functions in plastics. In particular, it is used to correct the whiteness of the material, reduce its cost, and also for some other purposes. In the production of rubber, chalk improves the wear resistance of products, as well as saving very expensive rubber and other components. Chalk is widely used in composite materials based on PVC. In significant concentrations, it is used in shoe and cable compounds. Moreover, for the manufacture of shells of cable products, it is used in almost all cases.

Chalk is widely used in non-plasticized PVC materials, in particular, for the production of molded products - window profiles, pipes, and even finishing. A property that hinders the industrial use of chalk is its ability to aggregate even with very little moisture. This leads to its caking in bunkers and difficulty in transportation. To eliminate this drawback, the chalk is subjected to hydrophobization, which consists in the application of surfactants that give the chalk the ability not to be wetted by water, which causes it to have a fairly good flowability. The hydrophobization process can be carried out by exposing the surface of the chalk particles to stearic acid. Chalk hydrophobization proceeds most fully when acid is supplied during the grinding process by spraying a hydrophobizing agent directly into the grinding chamber of the grinding unit.

Previously, due to the wide availability and very low cost, natural chalk or chemically precipitated chalk was used as a filler in polymer compositions in most cases. Well, in Lately, due to the increased requirements for the quality characteristics of plastic compounds and the appearance on the market of high-quality varieties of hydrophobic chalk and its analogues, large enterprises for the production of PVC compositions have almost completely switched to the use of hydrophobized chalk, despite its relatively high cost compared to conventional chalk. This made it possible to significantly improve the technology, improve the quality and even expand the range of PVC materials manufactured using it.

And this is far from all that could be written about the seemingly ordinary and extraordinary chalk.

Related materials

Dry mixtures perform the function of auxiliary materials for specialized purposes used in construction work and interior decoration. Dry building mixes are subdivided...

Almost any type of tiled finish requires filling tile joints with special grouts, which simultaneously perform both decorative and protective functions. Such...

Mosaic adhesive Litokol LitoPlus K55 Mosaic adhesive Litokol litoplus k55 is a composition based on white cement. Specialized...

Who did not eat chalk at school, which our teachers wrote on the blackboard. A neat white bar, almost everyone liked to gnaw. In stores you can find not only white, but also multi-colored crayons that we buy for our children so that they decorate the asphalt near our houses.

So, what is chalk, and what does it represent?

Many believe that chalk is an ordinary rock, crumbly, dirty and insoluble in water. The chemical composition of which includes calcium carbonate and a small amount of magnesium carbonate. But this is from one point of view.

But you know! It turns out that chalk was once an animal. In the ocean there are various tiny animals and plants. This is what a single-celled creature is, which is also called "foraminifera", in which the shell consists of lime. When a "foraminifera" dies, its shell sinks to the bottom of the oceans. A thick layer of shells is formed, from which foraminiferal limestones are formed, which become soft, and we already call them chalk. The carbonate part of the chalk mainly consists of three groups: powdered calcite, calcium crystals, organic residues (vegetable and animal).

In some areas, chalk lies close to the sea, which indicates that there was also water there before. The highest quality natural chalk is mined in England. In Russia, the largest chalk deposits occur in the Belgorod region.

It is practically not frost-resistant, because if it is frozen and thawed, it breaks into pieces. But this only speaks of its positive qualities. When moistened, its strength decreases, but if the humidity reaches 20%, then its plasticity increases, which sometimes makes it difficult to extract it, since it sticks to ladles.

For many years, people can not do without chalk and use it for their own purposes.

1. We know that no school can do without chalk, which is successfully used for writing on large school boards.

2. In medicine, chalk is used for calcium deficiency, as a food supplement. When used, it has a great effect on strengthening nails, teeth and bones.

3. In the sugar industry, it is used to purify beet juice.

4. In the glass industry, chalk is used as one of the components of the charge when melting glass, and chalk is also used for the production of matches.

5. In the printing industry, it is a necessary component of coated paper for printing illustrated publications.

6. In the rubber industry, it ranks first as it speeds up the rubber vulcanization process.

7. In the paper industry, it is used as a filler.

8. In the livestock industry, it is widely used for feeding and for the manufacture of animal feed.

9. And also chalk is perfectly used for painting fences, borders, walls, for protecting tree trunks from sunburn, for whitewashing ceilings. In the people we call it lime, which we extinguish with water, and then apply.

Who would have thought that the chalk that lies on the blackboard and with which our children draw on asphalt has such an interesting origin and is so widely used in various industries.

What is chalk made from? What is this connection? You will find answers to these and other questions in the article. It can be called a "witness of eras" that disappeared tens of millions of years ago. This compound has a biological source, therefore it has physical and chemical qualities. What chalk is made of, we will find out below.

Features of occurrence

Few people know what chalk is made of. Let's pay attention to its occurrence in nature. When dinosaurs lived on Earth (and this was about 80 million years ago), there was the Cretaceous period. In the tiny seas of that time, millions of small mollusks lived, which built their skeletons and shells from calcium in the water. In the bottom sediments, the remains of creatures accumulated in multi-meter layers and transformed into white chalk.

Mineral structure

Many people ask: "What is chalk made of?" In percentage terms, the following components of this mineral are distinguished:

• Up to 10% of chalk is found in the shells of tiny foraminifera mollusks.
• About 10% are fragments of the skeletons of multicellular animals, the simplest creatures that accumulate calcium in tissues.
• Up to 50% is finely dispersed crystalline calcite.
• Up to 3% - lump chalk (in the form of silicates). It is presented in the form of geological debris (remains of rocks, sand), carried by currents and winds into the Cretaceous deposits.
• Fragments of algal growths contain up to 40% of calcium salts. Microscopic living suspension in the seas is coccolithophores that create calcareous silt.

Chemical composition

So, you already know what kind of stone chalk is made of. Now let's look at its composition. It is known that the white mineral contains up to 50% calcium oxide, and approximately 2% magnesium oxide. What substances give color to this mineral?

Chalk can sometimes even contain 3-4% aluminum oxide, as well as some iron oxides. In this case, it will have a pink or red tint.

It is believed that the chemical formula of this rock is identical to the formula of potassium carbonate - CaCO 3.

It consists of:

• aluminum oxide - up to 4%;
• carbon dioxide - up to 43%;
• calcium oxides - from 47 to 55%;
• silicon dioxide - no more than 6%;
• magnesium oxide - no more than 2% of the total body weight;
• sometimes iron - no more than 0.5%.

By the way, the high content of silicon increases the density of the chalk.

Do you know what school chalk is made of? Can it be eaten? If a person does not have enough calcium in the body, he has a craving for eating chalk. Doctors are ambivalent about this issue. When it is under the influence of gastric juice (concentrated hydrochloric acid), it significantly changes its qualities.

Chalk goes through a large number of oxidative processes. As a result, it loses its primary neutrality, turns into a chemical aggressive compound, similar in properties to slaked lime (calcium hydroxide).

That is why the gastrointestinal mucosa is seriously affected by contact with an oxidized mineral.

If chalk is eaten in large quantities, this will provoke liming of the vessels. With a lack of calcium, it is much safer to take special medications, for example, calcium gluconate.

Doctors warn patients about the inadmissibility of using agricultural fodder, stationery, building chalk for food.

Application and extraction

How is chalk made? It is mainly obtained by open pit mining. The mined blocks are crushed, then immersed in water. With constant stirring, particles of calcium float to the surface. They are dried and used for a variety of purposes. By the way, it is unreasonable to use chalk in the form of masonry raw materials, since it has a low hardness.

Stones that have not undergone such processing are sent for firing. The result is lime, which has long been used to whitewash the ceilings inside buildings. Today, such a scope is almost absent, since other finishing materials have been created.

Today, chalk is added to various cement mixtures in order to give them additional softness. Also, the mineral is in demand when creating glass, plastics, rubber, rubber, mixtures of composite and paintwork materials.

In huge quantities, the breed is used in the carpet and linoleum industries. With its help, they regulate the viscous qualities of latex glue, improve the heat-saving properties of products, and give them strength.

Calcium is necessary for the manufacture of soil fertilizers and animal feed. Chalk powder is the base for creating many cosmetic products: lipstick, powder, creams. It is difficult to imagine the functioning of the paper and cardboard industry without this material.

Physico-chemical characteristics

Depending on the originality of the deposits, there can be significant differences in the natural properties of chalk. Humidity has a significant effect on the mineral. It does not dissolve in water, but forms a suspension. Calcium carbonate loses its strength when absorbing moisture. In this case, the plasticity of the material increases significantly.

This introduces serious problems in the processing and extraction of chalk, it sticks to the excavator bucket. It has little frost resistance. After thawing, it breaks up into a large number of small individual particles. This property is used in agriculture to reduce soil acidity.

How is chalk different from lime?

Despite the common roots, these materials differ in composition and properties. Both are considered environmentally friendly, but lime is obtained by burning natural limestone, and chalk contains carbon dioxide.

Would you like to distinguish lime from chalk on your own? Take a small handful of each raw material, grind to dust, and then rinse with a thin stream of water. The chalk will immediately disappear along with the water, but in order to remove the lime, you will have to work hard.

There are no traces of lime whitewash left. Chalk will remind of itself for a long time even after the repair is completed. Lime has excellent antiseptic properties, so it is used to protect shrubs and trees from insect infestation.

Application at school

Everyone should know what stone school chalk is made of. At first glance, this product looks nondescript. It is very relevant for students and teachers in educational institutions, it is spent by kids, drawing on city sidewalks. The consumer demands quality from any product, and chalk is no exception.

Many teachers complain that it corrodes the skin, falls off the board, gets their hands dirty, and irritates the vocal cords. What is the reason?

It is known that school chalk is 40% calcium carbonate and 60% gypsum or any other binding substance (starch, PVA glue). It also contains some metal oxides, magnesium carbonate, quartz impurities, marine fossils (foraminifers, radiolarians).

When layers of rock were brought to the surface from the seabed, they formed chalk cliffs, the most famous of which are located in England and France. In the Russian Federation, the largest deposits are located in the Belgorod and Voronezh regions, as well as in the Ulyanovsk, Saratov and Bryansk regions.

The oldest chalk manufacturing plant in Russia is located in Belgorod. In the area of ​​\u200b\u200bthis city, the mineral, like a rock, is mined today. It is from the Belgorod quarries that it is transported to all enterprises that produce material by the piece.

Production

How are crayons made? In Belgorod, chalk was made before and is now created by the extrusion method. In this case, the wet mineral in the form of thin sausages comes from a device similar to a meat grinder. The sausage is placed on a baking sheet, cut and dried in ovens. The result is round crayons. The technological originality of this product is that its “binding” is carried out with glue (most often PVA), which is not entirely safe for the health of babies (it is known that children eat white chalk, however, like adults). But she almost does not get her hands dirty, soft, pleasant to the touch.

Chalk has been used for drawing for a long time. Archaeologists are still discovering cave drawings made by this breed. Some artists drew sketches of their paintings. It was then that chalk, for convenience, acquired its generally accepted form in the form of a stick.

Since chalk is a loose and soft rock (powder), it is often mixed with binding substances - water and clay. After the resulting mass is placed in molds and dried. If a colored material is needed, a variety of impurities are added to the mixture. To obtain black crayons, for example, carbon is added, and for bright red - iron oxide.

Some manufacturers add dextrin or gypsum as a binder. And from this mixture, school chalk is further made. To obtain colored crayons, dyes are sometimes added at the last stage.

Basic requirements

We have already answered the question of what school chalk is made of. Its composition is quite varied. The basic requirements for writing material are as follows:

• should not crumble when writing on the board;
• should not get your hands dirty;
• the white product must be clean;
• no hard inclusions scratching the board.

Chalk from Pegas LLC (Klin) almost does not crumble, since it is quite dense. But the products manufactured by Centrum int LLC and Algem LLC make hands very dirty. Gypsum is used as a thickener in these samples, not starch.

By the way, chalk cannot corrode the skin of the hands, since the reaction of its environment is neutral. Continuous work with this mineral can cause dryness of the skin of the hands. Therefore, wash them more often, lubricate with a protective cream.