Mel is educated. Description of the physical property of chalk - strength

Chalk- it is a soft mountain porous sedimentary rock white color, is a type of limestone and is composed of the mineral calcium (calcite), which is also called calcium carbonate or CaCO3. It is formed at sea depths with the accumulation of small plates of calcite. The chalk contains a large number of magnesium carbonate and metal oxides.

Chalk has a very greater weather resistance than clay, with which it is commonly associated, thus forming high, steep cliffs where the chalk ridges meet the sea. Chalk mounds tend to form where chalk streaks reach the surface at an angle, thus forming a cliff. Since chalk is porous, it can contain a large amount of ground water, providing natural reservoirs that release water slowly due to dry seasons.

1. Clusters
2. Education
3. Compound
4. used

Chalk accumulations

The Cretaceous group of the European stratigraphic division originated during the Cretaceous period. It forms the famous White Cliffs of Dover in Kent (England), as well as the white slopes on the other side of the Strait of Dover. In Champagne (France), chalk caves are used to store wine. Some of the highest chalk cliffs in the world occur in Mons Klint (Denmark).

Chalk formation

Ninety million years ago Northern Europe silt accumulated in the lower part of the great sea. Protozoa, such as foraminifera, lived on marine debris that fell down from upper layers ocean. Their particles were made from calcite extracted from sea water.

Chalk composition

Chalk consists mainly of calcium carbonate (over 98%) with small amounts of silt and clay.

Chalk used

It is used in the production of quicklime and slaked lime, as a whitewash for buildings and tree trunks. In southeast England, Danehole is a prime example of ancient chalk quarries. In such places, flint was mined, which was then used in the manufacture of stone tools.

They write with chalk on school boards, mostly rough. Although natural chalk is traditionally used, modern blackboard chalks are usually made from the mineral gypsum (calcium sulfate), often supplied in compressed powder sticks about 10 cm long.

Sidewalk chalk is similar to school chalk, although it is larger and more colorful. It is used to paint on sidewalks, streets and roads. This is done mainly by both children and adult artists.

AT agriculture chalk is used to increase the pH in soils with high acidity. The most common forms are CaCO3 (calcium carbonate) and calcium oxide.

In tennis, chalk used to be used to mark the playing field. This has the advantage that if the ball hits the line, a cloud of chalk or pigment dust can be seen. Chalk has now been replaced by titanium dioxide.

In gymnastics, climbing, weightlifting and tug of war, chalk - now commonly magnesium - is applied to the hands to remove sweat and reduce slip.

Tailor's chalk is tough and is used to make temporary markings on fabrics. Nowadays, it is usually made from talc (magnesium silicate).

Toothpaste also usually contains a small amount of chalk to serve as a mild abrasive.

Chalk is used for very fine polishing of metals.

Chalk is a source of quicklime by thermal decomposition or slaked lime by quenching with water.

Drawing with chalk on asphalt is one of my favorite summer fun for babies. Of course, you can easily buy it in the nearest store, but it is much more interesting to create your own product: unique, multi-colored, which no one else has. Before you get started, you need to figure out how to make chalk so that it turns out the first time. There's a lot good recipes, but the gypsum-based option is the most successful.

materials

Get ready to learn how to make plaster-based chalk. For work you will need the following materials:

1. Plastic disposable plate small size. It is convenient to knead the mass in it, and then you can simply throw the dishes away and not waste time washing.
2. Plastic disposable spoon.
3. Gypsum. It is sold in craft stores or building departments. For the first time, only 1-2 cups of powder will be enough.
4. Warm water. You need enough liquid to bring the gypsum to the state of a thick paste.
5. Moulds. These can be plastic disposable cups, thick plastic straws for drinks, sand molds.
6. Acrylic or food grade paints different colors.
7. Sequins. These are optional ingredients, but girls love anything shiny.

Cooking process

Step-by-step instruction how to make homemade chalk will help you go through the whole process from start to finish. Pour 250 ml of dry gypsum into a plastic plate. Carefully pour in 125 ml warm water and 20 ml of acrylic paint of the desired shade. If you are using glitter, add it to the mix as well. Using a plastic spoon, quickly stir the mass until smooth. Do not hesitate, because you need to make chalk in 10-15 minutes, and then the plaster will harden. Put the mass into a mold, lightly tamp with a spoon, level the surface and leave to harden on a table or windowsill for 1-2 hours. Your homemade chalk is ready!

How to make chalk at home to make it dense and beautiful? Be sure to tamp the mass when laying it in the form, this is necessary to avoid cracks, gaps, and bumps. If you want a more intense crayon color, use more paint. Remember that gypsum hardens quickly, so you should not prepare a large portion at once, otherwise the mass will harden before you put the crayons into molds.

Options

To make it more interesting for kids, make special, unique crayons that no one else has. For example, you can make chalk giant size. To do this, use a disposable cup as a form and fill it with mass to the very top.

Another a good option to surprise your child's friends is to make striped multi-colored crayons. To do this, prepare several small portions of the gypsum mass, paint them acrylic paint in different colors and alternately put into the mold. If you are preparing chalk not for a child, but for yourself, for example, to apply patterns to fabric, you can make a regular white chalk and give it a comfortable fit.

Now you know how to make chalk with your own hands. All you need is to buy the right ingredients and get to work immediately!

Who among us does not know what chalk is? It can be called a "witness of epochs" that passed tens of millions of years ago. This compound is of biological origin, therefore it has numerous chemical and physical properties.

Features of origin

Arguing over what chalk is, let's pay attention to its appearance in nature. About 80 million years ago, when dinosaurs existed on Earth, there was the Cretaceous period. In the small seas of that time, millions of small mollusks lived, which built their shells and skeletons from the calcium contained in the water. The remains of creatures accumulated in layers of many meters in bottom sediments and turned into white chalk.

The composition of the mineral

As a percentage, there are several constituent parts this mineral:

• about 10% are fragments of the skeletons of the simplest creatures, multicellular animals that can accumulate calcium in tissues;
• up to 10% of chalk is part of the shell of small foraminifera mollusks;
• fragments of algae growths contain up to 40% calcium salts. A living microscopic suspension in the seas is coccolithophores, which create lime silt;
• up to 50% is crystalline finely dispersed calcite;
• lumpy chalk (in the form of silicates) - up to 3%. It is presented in the form of geological debris (sand, remains rocks), which are brought by winds and currents into the Cretaceous deposits.

Compound

Arguing over what chalk is, consider its composition. In chemistry, this name was given to calcium carbonate, which is a salt carbonic acid. Let's take a closer look at its composition. white chalk up to 50% contains calcium oxide, and about 2% magnesium oxide. What substances give color to this mineral? Studying what chalk is, we note that in some cases, it may contain even 3-4% aluminum oxide, as well as minimal amounts of iron oxides. How does this affect appearance mineral? In this case, the drawing chalk acquires a red or pink tint.

Can blackboard chalk be eaten? In case of a lack of calcium in the body, a person develops a craving for eating chalk. Doctors are ambivalent about this issue. When chalk is exposed to gastric juice (concentrated hydrochloric acid), it significantly changes its properties.

Chalk, having gone through many oxidative processes, loses its original neutrality, turns into an aggressive chemical compound, similar in properties to slaked lime (calcium hydroxide).

That is why, upon contact with oxidized chalk, the mucous membrane of the digestive organs is seriously affected.

If in large quantities eat chalk for the board, this provokes liming of the vessels. Much safer with a lack of calcium is the use of special medical preparations such as calcium gluconate.

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

Areas of use

It is not advisable to use chalk as a masonry material, since it has a slight hardness. How is this mineral mined? Basically, school chalk is obtained by open pit mining. The mined blocks are crushed, then lowered into the water.

With constant stirring, floating to the surface of calcium particles is observed. They are dried and used for various purposes. Stones that have not undergone such processing are sent for firing, as a result of which lime is formed.

Construction chalk

His long time used for whitewashing indoor ceilings. Currently, such a scope is practically absent, since other finishing materials have appeared.

Currently, chalk is introduced into the composition cement mixtures to give them extra softness.

Also, the mineral is in demand in the manufacture of glass, rubber, plastics, paints and varnishes, composite mixtures, rubber.

Chalk is used in large quantities in the linoleum and carpet industries. With its help, I regulate the viscous properties of latex glue, give products strength, and improve heat-saving characteristics.

The calcium mineral is also necessary for the production of soil fertilizers and animal feed. Chalk powder is the basis for creating numerous cosmetics: powders, creams, lipsticks. It is difficult to imagine without chalk and the functioning of the cardboard and paper industry.

Chemical-physical characteristics

Depending on the nature of the deposit, natural characteristics chalk can be significant differences. Humidity has a significant effect on the material. Chalk does not dissolve in water, it forms a suspension. When moisture is absorbed, calcium carbonate loses its strength, while the plasticity of the material increases significantly. It contributes serious problems in the extraction and processing of the mineral, it sticks to the excavator bucket. Chalk has low frost resistance. After thawing, the material breaks up into many separate small particles. This quality is used in agriculture to reduce the acidity of the soil.

Differences between lime and chalk

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

In order to independently distinguish between chalk and lime, you can take a small handful of each material, grind to a dusty appearance, then rinse with a small stream of water. Chalk will immediately be removed along with water, but in order to get rid of lime, you will have to work hard.

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

Finally

Chalk is a material that is familiar not only as a tool of work for teachers in schools, but also as a historical witness to the events that took place on our planet millions of years ago.

Its main part is made up of calcium deposits of the shells of the simplest prehistoric plants and microorganisms.

Cretaceous deposits are currently needed in various areas of production: in the creation of paints, the manufacture of cosmetics, the development of food additives. Cretaceous natural deposits often include various undesirable impurities: sand, stones, various mineral particles.

That is why the chalk mined in the deposits is first crushed, then mixed with water, getting a suspension. Heavy impurities settle to the bottom, light chalk particles are caught in a special container. After adding an adhesive composition to them, drying, chalk is obtained, suitable for drawing on a school board.

Among the new uses of chalk, one can single out its application on the playing field. Fine particles of this substance rise into the air, so the players can clearly see the lines made.

To remove sweat, fat, chalk powder is also in demand in some sports: weightlifting, gymnastics, rock climbing.

The finished product is an excellent component of toothpastes and powders. It is used as a filler in the manufacture of cardboard and paper products.

The raw quarried mineral is needed in the construction industry for the production of lime.

White chalk from FILA-GIOTTO, 100 pieces per pack, excellent quality.

The well-known blackboards with a dark surface, on which it is so convenient to write with chalk, still exist in many educational institutions the most developed countries. The fact is that they are the most convenient and safest, no matter what new items appear.

New marker boards can release ethers and cause asthma, and interactive whiteboards put unnecessary strain on the eyes. Therefore, the usual traditional board has no competitors.

The main thing is that the board is good, and chalk for it too.

12 non-shrinking white crayons. For drawing on board or asphalt. The crayons have a reduced dust emission, made with environmentally friendly clean materials and is easily washed off hands and clothes with water.

Not all chalk is good. One chalk crumbles, turning into dust; the other scratches the board, the third is almost invisible on the board, too pale.

One of the events is the appearance of the so-called crumbling crayons without dust. They are usually made using casein. These are crayons that do not stain hands and clothes, they are made using a special technology. Although crayons are called non-crumbling, nevertheless, their particles are still always present in the air of school premises. Ordinary good chalk is no worse.

Quality crayons do not crumble, form a minimum of chalk dust, have saturated colors; white chalk is clearly visible on the blackboard.

Previously (more recently) all boards for writing with chalk were exclusively wooden. They were covered matte paint usually black or dark brown. Such a background provided maximum contrast with the notes made in chalk. The modern school board has a metal base, which allows you to work not only with chalk, but also place auxiliary aids on magnets on it. Work surface paint is not used today by any board manufacturer; each company has its own special formulations, which are subject to increased requirements for resistance to chemical and mechanical stress. Boards made of varnished metal are very good.

School chalk - composition

For the best varieties chalk is applied exhausted a piece of chalk(in the trade it is called melted chalk). For the preparation of elutriated chalk, natural natural chalk is used. Such chalk is absolutely harmless and does not contain any foreign components. It is absolutely non-toxic.

Cheaper crayons can be prepared by stirring a mixture of light clay in water. good quality and chalk, but these can be drawn on asphalt, this is not for school boards.

School chalk is intended for children and therefore must be safe. No toxic impurities are used in the production of school chalk. The composition and all properties of the product must be indicated on the packaging of the chalk. School chalk should be made taking into account all existing production standards from environmentally friendly raw materials. Only then will chalk at school and at home be safe, and the possibility of poisoning is excluded. For schools, chalk is produced pressed and lumpy.

The basis of pressed chalk is calcium sulfate obtained from gypsum. In the manufacture of school chalk, which has a shape, starch and limestone are used.

For daily use in schools, lumpy natural chalk is most suitable, almost 100% calcium carbonate. This type of school chalk is the safest for the health of the child (and, importantly, the teacher).

Crayon manufacturers

The most famous domestic enterprises for the production of crayons are Algem, Elikont, Vakaris, Pegas, Quartet-1. The oldest plant in Russia for the production of chalk is located in Belgorod, and one of the very first on the market is the Algem company - it was the first to start casting chalk, having patented the composition and square shape. Cast white chalk contains gypsum in a minimal amount.

Chalk round "White Peps" from Maped, 100 pieces, white is one of the best views chalk for school. high quality calcium carbonate chalk. For children's creativity and schools. Doesn't crumble. Technology less dust. The round shape allows you to draw and draw without straining your hand.

Other good chalk companies are Pythagoras, Brauberg, Hatber, Koh-I-Noor. The best are Maped, Herlitz.

In the case of white crayons the most popular are bulk packs - 100 pieces at once. But colored crayons are bought in small boxes, 6-12 crayons each. This difference is explained very simply: colored crayons are aimed at children of primary and secondary school age, parents buy them for drawing on asphalt. White chalk is mainly a product for educational institutions, it is bought by schools, or parents for a class, for the whole academic year. The school can buy cheaper chalk, so it is best when parents themselves choose and buy high-quality chalk for your class - this is especially important for elementary school.

Just like black lead pencils, crayons have hardness grade. It depends on the degree of drying and the composition of the chalk. Harder chalk is designed for drawing on asphalt, chalk of medium hardness is best for blackboards, and soft chalk is used for tailoring.

White school crayons "Koh-i-Noor" classical form designed for writing and drawing on blackboards, asphalt and concrete. The crayons write easily and softly, leaving a clear and bright mark. In set 100 crayons white.

The effect of chalk on the body is due individual features each person. Like any dust, chalk dust also accumulates in the respiratory tract, causing irritation. Hence the cough, sore throat, sneezing. Sensitive skin can also be affected. Hands from chalk can itch, the skin can dry.

Eating chalk is an addiction of people with low iron content. This phenomenon is often observed in pregnant women and children. Moreover, chalk at school should be completely safe.

Chalk (in addition to the manufacture of crayons) is used in many other industries: in the sugar, rubber, paper, glass industries, in the production of soda. Chalk - required component coated paper used in printing for printing high-quality illustrated publications. Ground chalk is widely used as a material for whitewashing, painting fences, walls, borders, to protect tree trunks from sunburn.

How to make your own chalk from chalk

You can even make crayons yourself if you know where to get clean chalk. In the manufacture of colored chalk, chalk powder is mixed with an appropriate amount of mineral paints and kneaded in an aqueous solution of wood glue, gum arabic or dextrin, brewer's yeast, oatmeal paste are also used. Gypsum, alabaster, and lead white can also be used as a filler for white crayons, but these materials are too expensive. To make the chalk soft, you can add soap (in the form soapy water), oil or wax. Ready dried crayons are dipped in oil, which improves their color and makes them softer. Carefully mixed chalk, dye and binder are laid out on a table or on boards, which are pre-coated with 5-6 sheets of waste paper or any paper that is not a pity. The paper absorbs moisture, and the mass acquires a thick consistency. When the mass becomes thick enough and you can take it in your hands so that it does not stick, take a piece of the mass the size of a nut, roll it into a ball, and then roll it into a cylinder with your palm. Next, the cylinder is rolled with a smooth board so that it becomes even and smooth. The molded crayons are placed on boards, covered with paper and dried in the shade.

If you work with chalk a lot...

White school crayons "Crayola" made from environmentally friendly safe materials, they do not form dust and do not crumble. 12 pieces.

If a permanent job with chalk causes dry skin of the hands and cough, these symptoms can eventually lead to allergic diseases.

To prevent allergic reactions to chalk, it is recommended:

1. while working with chalk, wash your hands often with softening toilet soap: well suited glycerin, lanolin, vaseline and milk soap, liquid mild soap, as well as Dove cream soap, etc.;
2. after each lesson, it is advisable to lubricate the hands with a moisturizing hand cream;
3. wash chalk from the board only with a damp cloth - so there is much less chalk dust;
4. Rinse the chalk-cleaning cloth off the board as often as possible to keep it clean.

Chalk- this is not only a familiar subject from school times, but also a witness to eras that have passed millions of years ago.

Most of the composition of the chalk is formed by calcium deposits of the shells of prehistoric microorganisms and protozoa. Cretaceous deposits, including processed ones, are used today in various fields - from the production of paints and food additives to cosmetics.

How did chalk come about?

Chalk is an natural material and is mined as a mineral. Basically, it is calcium deposits formed from the remains of ancient terrestrial organisms.

In the production of chalk and chalk-containing products, already processed chalk is used.

Natural chalk deposits often contain various undesirable impurities - stones, sand and various mineral particles. Therefore, the chalk mined in the deposits is broken and mixed with water in such a way as to obtain a suspension.

At the same time, heavy impurities sink to the bottom, and light calcium particles are sent to a special tank, where, after adding a special adhesive, they are dried, turning into chalk, which can be painted on.

Raw chalk from chalk quarries used for construction purposes to obtain lime.

We bring to your attention another article about the origin, its composition and medicinal properties.

What is chalk and what does it consist of?

Chalk contains:

• calcium oxides - from 47 to 55%;
• carbon dioxide - up to 43%;
• silicon dioxide - no more than 6%;
• aluminum oxide - up to 4%;
• magnesium oxide - no more than 2% of the total mass of chalk;
• chalk may also contain iron, however, its concentration usually does not exceed 0.5%.

Chalk accumulations

The accumulation of Cretaceous deposits began in the so-called Cretaceous period, covering a period of 80 million years. About 20% of the Earth's sedimentary rocks include chalk.

Chalk deposits:

• To the largest chalk deposits include the White Cliffs of Dover, the chalk caves in the French city of Champagne and the chalk cliffs of Mons Klint in Denmark.
• On Russian territory Cretaceous mountain deposits up to 600 meters thick are located south of Kharkov.
• The largest deposits of the Voronezh region- Kopanischenskoe, Rossoshskoe and Buturlinskoe. The city of Belgorod, presumably, got its name from the local chalk deposits.

Chalk formation

The formation and accumulation of limestone deposits took place over eighty million years.

foraminifera- single-celled organisms, the shells of which served as the basis for the formation of today's Cretaceous deposits. After the death of these protozoa, their shells sank to the bottom of the ocean, creating foraminiferal limestones.

These formations, along with the remains of unicellular coccolithophorid plants, are an integral part of today's Cretaceous accumulations. Compressed under water pressure, the remains of coccolithophores and shells of ancient mollusks have been supplemented by the skeletal remains of fish and animals for millions of years.

Despite the fact that back in 1953, scientists announced the predominant role of plants in the formation of limestone rocks, among the inhabitants there is still an opinion about the primacy of foraminifers.

Compound

Cretaceous deposits include:

• Skeleton fragments– approximately 10%. These are the remains of not only protozoa, but also large multicellular animals.
• Shells of ancient molluscs- ten %. Among them were animals with limestone shells - foraminifera.
• Particles of calcareous growth of algae- no more than 40%. Most of the limestone deposits, contrary to popular belief, were formed from the remains of the simplest plants - coccolithophorids, and not from the shells of foraminifers. Coccolithophores have not died out, they feel great in the vastness of the world's oceans today, taking part in the exchange of carbon between the ocean and the atmosphere.
• Crushed crystalline calcite- no more than 50%. These are natural mineral formations of complex origin.
• Insoluble silicates- until 3%. These are minerals of geological origin - sand, fragments of rocks brought into the chalk deposits by wind and water. Properties of chalk

Humidity, which affects its strength and plasticity, has a great influence on the properties of chalk. An increase in humidity leads to deformation, while in a dry environment, chalk can crumble even from slight pressure.

Moisture-saturated rock sticks to construction tools. That's why construction works using calcium carbonate is carried out in countries with a hot and arid climate. An excellent example of an ancient limestone building is Egyptian pyramid Cheops (Khufu).

At sub-zero temperature the rock is prone to disintegration into fragments of a few millimeters.

Chalk cost

The price of chalk will depend primarily on its type (processing) and purpose:

• for drawing on asphalt will cost no more 200-400 rubles for packing.
• white crayons without dyes will cost about 100 rubles .
• farm chalk I buy in large quantities, shipping it in several tons. The cost of each ton of ground chalk is 3000-5000 rubles.
• Price for food chalk used in medicine and food supplements (E-170) - from 40 to 300 rubles for 100 grams. The stone was also used in medicine).

Chalk application

Today, chalk is a fairly widespread material for various industries.

So, chalk is used in the following areas:

1. Chalk paints applied to interior decoration during construction and renovation works.
2. Chalk is part of cement mixtures providing them with softness and elasticity.
3. Ground natural chalk actively used for glass production.
4. Chalk is part of the farm feed and is used to fertilize the soil.
5. Chalk is the basis for cosmetics- lipstick, foundation, powder, etc. It is the chalk in the composition of the foundation that absorbs excess fat and protects the skin from shine.
6. Chalk is also used for domestic purposes as an absorbent and whitening agent.
7. Production of tooth powders and pastes also not without the use of chalk.
8. In the production of paper and cardboard products finely dispersed (crushed) chalk is used as a filler and bleach for paper. Chalk treated with stearic acid has hydrophobic properties. It is also used in the paper industry. The content of chalk in paper improves print quality and reduces the likelihood of wear and tear of printing equipment.
9. Not so long ago, chalk was used to mark the playing field.. The suspension rising into the air after the ball hit the line was easy to see. Today titanium dioxide is used instead of chalk.
10. To remove sweat and reduce the risk of slipping, chalk is used in sports such as weightlifting, gymnastics and rock climbing today.

Can you eat chalk?

A lack of calcium and other beneficial trace elements can lead to a desire to eat chalk. During pregnancy, with anemia, some people have a strong craving for eating chalk, so the question of the safety of this mineral for the body arises for many.

Of course, one or two small pieces of pure chalk will not bring much harm to the body. However, it must be remembered that chalk without impurities is not available for free sale and it is practically impossible to get it, except perhaps in a pharmacy in the form of calcium gluconate. In the most common product - "school chalk", during the production they add glue and various dyes that are toxic to the body.

The use of chalk in large quantities can cause calcification of blood vessels, the formation of kidney stones and provoke problems with the digestive tract.

In addition to the detrimental effect of impurities that make up construction and chancellor chalk, it is characterized by oxidation when interacting with gastric juice, which turns it into a harmful chemical reagent.

What to do if you want to eat chalk?

The desire to eat chalk is often a signal of a lack of calcium in the body. The reasons for its deficiency can be a monotonous diet, long-term stressful conditions, weakening of the body after serious illnesses and pregnancy.

Given that during pregnancy it is calcium that is the basis for the formation of the nervous and skeletal system of the child, the lack of this mineral must be filled. In this case, a variety of diet is not able to completely solve the problem, so doctors strongly recommend taking special vitamin complexes during pregnancy.

Due to the fact that the neural tube of the fetus is formed on early dates, in order to minimize the risks of improper development, it is necessary to start taking vitamins even during pregnancy planning. Anemia and calcium deficiency in the body often appear with heavy and long periods.

With symptoms of severe calcium deficiency (convulsions, marked deterioration and blanching of skin and hair) you can take calcium gluconate tablets. Unlike stationery and other types of industrial chalk, they are safe, however, with prolonged use they can lead to constipation.

As a rule, the craving for eating chalk ends after the diet is expanded to include dairy products, chicken eggs and fresh greens.

In some cases, the desire to eat inedible and inedible substances can be a sign of a mental disorder. Consequence of the use of inedible objects are intestinal obstruction and nutritional deficiencies.