Building gypsum: description, types, properties, photos

Construction gypsum Are binders obtained from gypsum stone or chemical waste.

When firing gypsum stone, chemically bound water is separated and, depending on the temperature, various forms of gypsum are formed. At 100 degrees Celsius, hemihydrated gypsum begins to form. When mixed in water, calcium sulfate dihydrate is again formed. This closed cycle was discovered about 20 thousand years ago. People built hearths from gypsum stone and probably noticed how the scattered burnt gypsum turns into stone again in the rain. In Sumerian and Babylonian cuneiforms, there are references to gypsum and its use.

The availability of raw materials, simplicity of technology and low energy consumption of production (4-5 times less than for the production of Portland cement) make gypsum a cheap and attractive binder.

Plaster history

Gypsum is one of the oldest mineral binders. In Asia Minor, gypsum was used for decorative purposes for 9 thousand years BC. During archaeological excavations in Israel, floors covered with plaster were found 16 thousand years BC. Gypsum was also known in ancient Egypt, it was used in the construction of the pyramids. Knowledge of the production of plaster of paris from Egypt spread to the island of Crete, where in the palace of King Knossos, many of the outer walls were built of plaster stone. The joints in the masonry were filled with plaster mortar. Further information about gypsum came to Rome through Greece. From Rome, information about gypsum spread to central and northern Europe. Gypsum was used especially skillfully in France. After the displacement of the Romans from central Europe, knowledge about the production and use of gypsum was lost in all regions north of the Alps.

And only from the 11th century the use of plaster began to increase again. Under the influence of monasteries, the technology spread, according to which the voids inside half-timbered buildings were filled with a mixture of gypsum with hay or horsehair. In the early Middle Ages in Germany, especially in Thuringia, the use of plaster was known for floor screeds, masonry mortars, decorative items and monuments. In Saxe-Anhalt, there are remains of plaster floors from the 11th century.

Masonry and screeds made in those ancient times are distinguished by their extraordinary durability. Their strength is comparable to that of normal concrete.

The peculiarity of these medieval gypsum mortars is that the binders and fillers consisted of identical materials. As fillers used gypsum stone, crushed to round grains, not pointed and not lamellar. After the solution hardens, a coherent structure is formed, consisting only of calcium sulfate dihydrate.

Another feature of medieval mortars is the high fineness of gypsum grinding and extremely low water demand. The water to binder ratio is less than 0.4. The solution contains few air pores, its density is approximately 2.0 g / cm3. Later gypsum solutions were produced with a much higher water demand, therefore their density and strength are much lower.

Definition and main characteristics

Stucco is a natural mineral from the sulfate class. Its chemical formula is CaSO 42H 2O (calcium sulfate hydrate). Since the molecule of a substance contains 2 atoms of water, it is also called calcium diaquasulfate.

A fine-crystalline structure with a large number of pores is both a positive quality (gives lightness and resistance to high temperatures) and negative (does not provide strength and moisture resistance).

The optimum porosity of the product after hardening is 40-60%. If it is higher, the product becomes weaker and breaks easily. The porosity depends on the amount of water used when mixing the solution.

The specific gravity of the material is 2.6-2.75 g / cm³. Density in a loose state is 800-1100 g / m³, when compacted it can reach 1450 kg / m³.

What is plaster of paris externally? It is a fairly finely ground powder, usually white or grayish, sometimes with a yellow or pink tint. The smell is very weak, intensified with the addition of water.

A liquid solution (dough) is a gray mass with a specific odor. After drying, it becomes white or light gray, the surface of the finished product is smooth to the touch.

Gypsum has so many advantages that it can be called a truly unique material.

  • Environmental friendliness and naturalness. Gypsum is a completely natural material, it is still mined in an old-fashioned way. It is as environmentally friendly as possible, which puts such raw materials many steps higher than any modern building material.
  • The ability to improve the microclimate. It has long been noticed that in rooms decorated with stucco molding, it is very easy to breathe, even if it is hot or raining outside. This is easily explained by the fact that the frozen gypsum solution has the ability to exchange moisture: increased moisture is absorbed by it, and with an insufficient amount of water in the air, it is released.
  • Responsive to restoration. Unlike glass, leather, wood, stone and even metal, stucco molding is subject to complete restoration. With well-done renovations, she can look perfect, even if she is a hundred years old. Try to recreate a lost piece of a china or stone bowl so that it looks like new. Agree, this is impossible. But the plaster products after restoration do not contain visible traces of the master's work.
  • Endless decor possibilities. In skillful hands, plaster takes any shape, even the smallest details are visible on it. It can be stained, patinated, coated with various compounds that give shine or other visual qualities. Moreover, it is not subject to shrinkage, so the finished decor will remain in its original form as much as the owner of the room wants.

Stamps

Depending on the strength, gypsum binders are divided into 12 types, or grades. They are designated by the letter G and numbers from 2 to 25: G-2, G-3, G-4, G-5, G-6, G-7, G-10, G-13, G-16, G-19 , G-22, G-25. The digital part denotes the compressive strength: for example, for the G-5 brand it will be 0.5 MPa (5 kgf / cm²). Strength tests are carried out on standard 4x4x16 cm beams. After casting, they dry in the open air for 2 hours. The whole beams are then tested for bending and the halves for compression. Depending on the results, the samples are assigned the appropriate grade.

In turn, the stucco brands are divided into two groups:

  • Low-fired - these include construction, molding and high-strength.
  • High-fired - estrich gypsum and anhydrite cement created at high (up to 1000 ° C) temperatures.

A kind of plaster

Β-modification gypsum

Gypsum β-modification is obtained at a temperature of 150-180 ° C in apparatus communicating with the atmosphere. The product of grinding β-modification gypsum into a fine powder before or after processing is called stucco or alabaster; with finer grinding, molding gypsum or, when using raw materials of increased purity, medical gypsum is obtained.

Α-modification gypsum

Gypsum α-modification is obtained by low-temperature (95-130 ° C) heat treatment in hermetically sealed furnaces. High-strength gypsum is made of it.

Alabaster

Alabaster (from gr. alebastros - white) - a fast-hardening air binder, consisting of semi-aqueous calcium sulfate CaSO 4• 0.5H 2O obtained by low-temperature processing of gypsum raw materials.

Alabaster - β-modification gypsum, a powdery binder obtained by heat treatment in open ovens at a temperature of 150-180 degrees of natural two-water gypsum CaSO 4 ·2H 2O. The resulting product is ground into a fine powder. With finer grinding, a molding plaster is obtained. Raw materials of high purity are used for medical plaster.

Anhydrite

Anhydrite is a natural anhydrous gypsum. Anhydrite binder slowly sets and hardens slowly, composed of anhydrous calcium sulfate CaSO 4and hardening activators.

Estrich plaster

High-fired estrich gypsum is obtained by firing natural gypsum stone CaSO 4• 2H 2O to high temperatures (800-950 ° C). In this case, its partial dissociation occurs with the formation of CaO, which serves as an activator of the hardening of anhydrite. The final hardening product of such a binder is gypsum dihydrate, which determines the performance properties of the material.

The technological properties of estrich gypsum differ significantly from those of ordinary gypsum. Setting time for estrich plaster: start no earlier than 2 hours, end - not standardized. Due to the reduced water demand (for estrich gypsum it is 30-35% versus 50-60% for ordinary gypsum), estrich gypsum, after hardening, forms a denser and more durable material.

The strength of the samples - cubes from a solution of a rigid consistency of the composition - binder: sand = 1: 3 after 28 days of hardening in humid conditions - 10-20 MPa. According to this indicator, the brand of estrich plaster is established: 100, 150 or 200 (kgf / cm 2).

Estrich gypsum was used in the late 19th and early 20th centuries. for masonry and plastering mortars (including for the production of artificial marble), installation of seamless floors, bases for clean floors, etc. Currently, this binder is used to a limited extent.

Compressive and flexural strength

The brand of gypsum is determined by testing the compression and bending of standard samples - beams 4 x 4 x 16 cm 2 hours after their formation. During this time, the hydration and crystallization of gypsum ends.

12 grades of gypsum have been established in terms of strength from 2 to 25 (the figure shows the lower ultimate strength in compression of this grade of gypsum in MPa). In construction, gypsum grades from 4 to 7 are mainly used.

According to GOST 125-79 (ST SEV 826-77), depending on the ultimate compressive strength, the following brands of gypsum binders are distinguished:

Binder grade Minimum tensile strength of sample beams with dimensions of 40x40x160 mm at the age of 2 hours, MPa (kgf / cm 2), not less
under compression bending
G-2 2 (20) 1.2 (12)
G-3 3 (30) 1.8 (18)
G-4 4 (40) 2.0 (20)
G-5 5 (50) 2.5 (25)
G-6 6 (60) 3.0 (30)
G-7 7 (70) 3.5 (35)
G-10 10 (100) 4.5 (45)
G-13 13 (130) 5.5 (55)
G-16 16 (160) 6.0 (60)
G-19 19 (190) 6.5 (65)
G-22 22 (220) 7.0 (70)
G-25 25 (250) 8.0 (80)

When moistened, the hardened gypsum not only significantly (2-3 times) reduces strength, but also exhibits an undesirable property - creep - a slow irreversible change in size and shape under load.

Production technology

Deposits of natural gypsum are sedimentary, residual or metasomatic (by the type of formation). In Russia, large deposits are mostly sedimentary. In the development of most deposits, production is carried out by open-pit mining, but due to natural conditions in some deposits, it is necessary to use the chamber-and-pillar method.

The extracted raw materials are delivered to the processing plant. There, it is crushed first on a screw crusher and then on a hammer mill. After that, the resulting powder is dried and subjected to heat treatment - firing in special digesters. This is the most common technology for the production of stucco, but there are others. For example, roasting can be carried out in rotary kilns or in combined grinding and roasting mills.

Most often, firing takes place at a temperature of 150-180 ° C. Drying takes place in two ways:

  • In an open oven, water comes out in the form of steam. The resulting β-gypsum is fibrous in structure with a loose crystal lattice. It is rather porous, and the pores are located both between the fibers and inside the crystals. It is usually used in construction as a molding or binding material.
  • In an autoclave - water is removed by the drip method. When processing under high pressure, moisture begins to evolve even at low temperatures (from 60 ° C). The result is a less porous and more durable alabaster that can be crushed into the finest powder. Also, the autoclave dehydration method can reduce the amount of impurities and get a very clean result. It is noticeably more expensive, so it is used mainly in medicine, for example, for dental impressions, and art - sculptures and decor from it look neat and are more durable.

After dehydration, the chemical formula looks like CaSO 40.5H 2O. The obtained semi-aqueous gypsum is crushed into fine powder and packed in paper or polyethylene bags.

Working with plaster.

In practice, when working with gypsum, a solution of pure gypsum is mainly used, less often with a filler. Depending on the type of work, the gypsum solution can have a different degree of consistency: liquid, medium or normal or thick. To prepare a liquid solution for 1 kg of gypsum, you will need about 0.7 liters of water, an average or normal solution - for 1.5 kg of gypsum 1 liter of water and for a thick solution - for 2 kg of gypsum 1 liter of water. the prepared container is first poured with the required amount of water and gypsum is gradually poured into it with constant thorough mixing. with this method of preparation, a homogeneous mass is obtained without admixtures of lumps of unmixed gypsum. You should not mix the gypsum solution that has already begun to set, since at the same time the gypsum begins to rejuvenate and practically loses its strength. When working with gypsum, you should take into account the rapid setting of the gypsum solution and prepare in small portions. To slow down the setting time of the gypsum solution, set retarders are used, which have already been mentioned above. When used as a retarder of the glue solution, it is poured into the water prepared for mixing, thoroughly mixed and gypsum is mixed in this water. The glue solution should be prepared for one day of work.

Dignity

When choosing building materials, the decisive factors are its price, ease of use and quick hardening. But it is worth considering other, equally important characteristics of plaster of paris:

  • Environmental friendliness ... Completely natural material, hypoallergenic, does not contain harmful substances. Helps maintain a favorable microclimate in the room.
  • Durability. Buildings made of it withstand at least 15-20 freeze-thaw cycles. In a dry climate without sudden changes in temperature, buildings and products are particularly well preserved.
  • Fire safety. The mineral itself is not flammable, it can withstand prolonged exposure to temperatures of 600-700 ° C, and the release of moisture when exposed to high temperatures slows down the spread of fire.
  • Low thermal conductivity. It can be used for insulation of premises.
  • Ease. With high strength, it has a low density, only 1200-1500 kg / m³. This makes it half the weight of cement.
  • Availability. Among the binders, gypsum is the most affordable. It is easy to obtain and does not require complex or energy-intensive technologies to process.

disadvantages

There are no building materials without flaws. In calcium dihydrate (gypsum), they are mainly associated with water:

  • Hygroscopicity. Due to the porous structure, mineral raw materials absorb large amounts of water. This property limits the use of stucco in humid environments.
  • Low moisture resistance. As a result of getting wet, there is a high probability of deformation of the product or structure.
  • Corrosion of metal reinforcement laid inside building blocks. Therefore, for the reinforcement of buildings, it is better to use natural fibrous materials - wood, reeds, etc.
  • Low strength. A side effect of the porous structure. Gypsum is easy to scratch, and sometimes you don't even need tools.

Moisture resistance can be improved with filler additives. They can be lime, oleic acid, clay, granulated blast furnace slag, a mixture of soluble glass and dextrin. Another option is to apply topcoats to the finished product to prevent water from entering the pores.

Gypsum as a binder

Gypsum binders are materials based on semi-aqueous gypsum or anhydrite. Refers to airy binders.

Depending on the method of production, gypsum binders (HS) substances are divided into three main groups:

  • I - binders obtained by heat treatment of gypsum raw materials: low-calcined (calcining and cooking) and high-calcined: α- or β-calcium sulfate hemihydrate (or a mixture thereof), as well as soluble anhydrite (completely dehydrated gypsum or even partially dissociated anhydrite containing a small amount free calcium oxide).
  • II - binders obtained without heat treatment (non-fired): natural anhydrite, special additives are introduced to activate hardening.
  • III - binders obtained by mixing gypsum binders of groups I or II with various components (lime, Portland cement and its varieties, active mineral additives, chemical additives, etc.).

Binders of groups I and II are non-water resistant (air) gypsum binders (NGV). Group III binders belong, with some exceptions, to waterproof gypsum binders (HBV).

For the production of the gypsum binders indicated in Table 1.1, natural gypsum, anhydrite raw materials or gypsum-containing waste are used.

Depending on the temperature of heat treatment, gypsum binders are divided into two groups:

Low firing group

Low-fired (actually gypsum, based on CaSO 4• 0.5H 2O) obtained at a temperature of 120-180 ° C. They are characterized by fast hardening and relatively low strength. These include:

  • plaster of paris, including alabaster;
  • molding plaster;
  • high-strength gypsum;
  • medical plaster;

High firing group

High-calcined (anhydrite, based on CaSO 4) obtained at temperatures of 600-900 ° C. Anhydrite binders differ from gypsum binders in slow hardening and higher strength. These include:

  • estrich gypsum (high-calcined gypsum);
  • anhydrite cement;
  • finishing cement.

Gripping plaster

According to the setting time determined on the Vika device, gypsum is divided into three groups (A, B, C):

Binder type Hardening time index Setting time, min
start, not earlier end, no later
Fast hardening А215
Normally hardening Б6thirty
Slow hardening В20 Do not standardize

The hardening time of gypsum depends on the type of gypsum, the amount of water, the temperature of the water, and the dispersion of the gypsum. With a low water content, the mixture is poorly poured, hardens quickly, emits an increased amount of heat, with a simultaneous increase in the amount of volume.

The hardening time of gypsum increases with increasing water temperature, so cold water should be used.

They slow down the setting of gypsum with the help of additives:

  • joiner's glue;
  • sulfite alcohol stillage (SSB);
  • technical lignosulfonate (LST);
  • keratin retarder;
  • boric acid;
  • borax;
  • polymer dispersions (for example, PVA).

Plaster hardening

The chemistry of gypsum hardening is the transition of hemihydrate calcium sulfate, when mixed with water, into dihydrate: CaSO 4• 0.5H 2O + 1.5H 2O → CaSO 4• 2H 2A. Outwardly, this is expressed in the transformation of plastic dough into a solid stone-like mass.

The reason for this behavior of gypsum is that semi-aqueous gypsum dissolves in water almost 4 times better than dihydrate (the solubility is 8 and 2 g / l, respectively, in terms of CaSO 4). When mixed with water, semi-aqueous gypsum dissolves to form a saturated solution and immediately hydrates, forming a dihydrate, in relation to which the solution is supersaturated. Crystals of gypsum dihydrate precipitate, and semi-aqueous gypsum begins to dissolve again, etc.

In the future, the process can follow the path of direct hydration of gypsum in the solid phase. The final stage of hardening, ending in 1-2 hours, is the formation of a crystalline intergrowth of fairly large crystals of gypsum dihydrate.

Part of the volume of this intergrowth is occupied by water (more precisely, a saturated solution of CaSO 4• 2H 2O in water), which has not interacted with gypsum. If you dry the hardened gypsum, then its strength will noticeably (1.5-2 times) increase due to additional crystallization of gypsum from the above solution at the contact points of the already formed crystals.

When re-wetting, the process proceeds in the reverse order, and the gypsum loses some of its strength. The reason for the presence of free water in the hardened gypsum is explained by the fact that for the hydration of gypsum about 20% of its mass is needed, and for the formation of a plastic gypsum dough - 50-60% of water. After hardening of such a dough, 30-40% of free water will remain in it, which is about half of the volume of the material. This volume of water forms pores temporarily occupied by water, and the porosity of a material, as is known, determines many of its properties (density, strength, thermal conductivity, etc.).

The difference between the amount of water required to harden the binder and to obtain a formable dough from it is the main problem in the technology of materials based on mineral binders. For gypsum, the problem of reducing water demand and, accordingly, reducing porosity and increasing strength was solved by obtaining gypsum by heat treatment not in air, but in saturated steam (in an autoclave at a pressure of 0.3-0.4 MPa) or in salt solutions (CaCl 2• MgCl 2and etc.). Under these conditions, another crystalline modification of semi-aqueous gypsum is formed - α-gypsum, which has a water demand of 35-40%. Gypsum α

- modifications are called high-strength gypsum, since, due to the reduced water demand, it forms a less porous and more durable stone during hardening than conventional β-modification gypsum. Due to the difficulties of production, high-strength gypsum has not found widespread use in construction.

Plaster stone is almost everywhere: in the walls of houses, in jewelry, in a hospital, in works of art.

The many-sided stone always looks different.

From antiquity to the present day

The history of a simple stone goes back to antiquity. Pliny has many descriptions of the types of alabaster, about the places of its extraction. In the writings of the scientist, this mineral is called alabastrites. They used it in construction, for the manufacture of vessels, lamps, sarcophagi.

гипс порода

In Egypt, on a relief from the tomb of the ruler of Hermopolis nome Tkhutihotep, the transportation of a statue of this ruler sitting on a throne is depicted: according to the inscription, this statue is approx. 6.50 m, was made of Khatnub alabaster.

Alabaster vessels were considered the best for storing incense.

Mineral properties

The chemical formula of the rock is CaSO4 2H2O.

Mineral class - sulfates.

Characteristics:

  1. The mineral can be colorless or colored in different colors and shades - pinkish, gray with shades of red, brown, blue.
  2. In crystals the luster is glassy, ​​in fibrous structures it is silky.
  3. Hardness 2 on the Mohs scale.
  4. Cleavage is very perfect in one direction (it easily splits into thin leaves).

Gypsum properties:

  • soluble in water (best solubility at 37-38 ° C);
  • resistant to mechanical stress;
  • has low thermal conductivity;
  • high resistance to high temperatures. On contact with an open flame for 6-7 hours, signs of destruction appear.

Gypsum material is hypoallergenic.

Formula CaSO4 2H2O
Physical properties
Color White, shades of gray and red
Line color White
Shine Glass to pearlescent
Hardness 1.5-2.0
Cleavage Very perfect
Break Uneven; flexible but not elastic
Density 2.2-2.4 g / cm³
Crystallographic properties
Syngonia Monoclinic
Optical properties
Refractive index 1.52

Varieties

The minerals of gypsum will differ according to their place of "origin". Druze, single crystals, "desert roses", "swallow tails" are formed in the soils of deserts.

Types of gypsum:

  • alabaster - a fine-grained mineral of different colors;
  • selenite - the structure is parallel-needle-like, has a silky sheen; Selenite unprocessed peach

    Selenite unprocessed peach

  • Maryino glass (maiden ice) - is formed by the separation of large tabular crystals.

The Mineralogical Encyclopedia of 1790 mentions:

"Mary's glass ... one of the varieties of gypsum: mirrored gypsum, zelenite, donkey's mirror, Mary's glass consists of such leaves that, no matter how thin, can be divided into other leaves."

Place of Birth

Gypsum is a rock and rock-forming mineral.

The origin of the breed is ancient. It was formed during the Permian period in the process of evaporation and deposition of large, shallow water bodies. Secondary gypsum is formed where sulfate and calcium mineral waters are mixed.

гипс

Gypsum can be mined in Russia, they are rich in:

  • Nizhny Novgorod Region;
  • Perm Territory;
  • Volgograd region;
  • Karachay-Cherkessia;
  • Krasnodar region.

Cognitively: half of the world's mineral reserves are located in Russia.

Deposits abroad are possessed by:

  • Canada;
  • USA;
  • many European countries;
  • Mexico.

Desert Rose

In the Sahara, there are unusual plaster formations that resemble flowers. They are called “desert roses”. Some reach a weight of up to 400 kg, and their height is more than a meter. Lovers give these "roses" as a sign of love.

роза пустыни

Stone flowers form when it rains over gypsum-rich sands. In the heat, moisture quickly evaporates, forming "petals" -crystals of gypsum.

Application

Plaster is suitable for making dental impressions (dentistry). Sculptural plaster is used in the manufacture of street sculptures, interior items (vases, countertops, souvenirs).

Interesting: during the war in the United States, the Oscar statuettes - the highest cinema award - were made not of metal, but of plaster. After the war, these awards were replaced by traditional metal (gold-plated alloy

tin

и

lead

).

The mineral is used to produce:

  1. Construction mixtures (plaster, putty, self-leveling floors).
  2. Gypsum concrete, drywall.
  3. Decorative stone, marble imitation.
  4. Part of Portland cement.
  5. Ammonium sulfate (fertilizer).
  6. Higher grades of writing paper (as filler).
  7. As a flux in nickel smelting.

The use of the mineral as a marble imitator in the production of facing slabs is due to the properties of gypsum. These are high decorative qualities, the ability to be easily polished and processed.

Informative: the blocks of the Cheops pyramid are fastened with plaster mortar.

Pros and cons of stucco 🏗️

Dignity disadvantages
Gypsum mixes are the most affordable and cheapest Low strength; the plaster coating is easy to damage
Withstands high temperatures in case of fire. Moisture released during the thermal process reduces the destructive effect of fire Gypsum actively absorbs water, so its use in a humid environment is undesirable
Eco-friendly, natural material. Creates a favorable microclimate Metal reinforcement inside gypsum masses corrodes quickly
Has a low thermal conductivity, which will help keep the room warm Heavily wet gypsum products can deform

Magic

The effect of the mineral on humans is safe, and it is ideal for allergy sufferers.

Selenite crafts have properties that pacify passions. Selenite magic for impetuous people who are not always in control.

The selenite amulet has meaning for the narcissistic ignorant. For a person who is "always right", this amulet is irreplaceable. He brings the "infallible" back to earth.

Such little things are contraindicated for unsure of themselves, too soft people.

Souvenir care

Selenite products are very soft and should be handled with care.

It is easy to distinguish delicate selenite - it is worth pressing harder with your fingernail, and a trace will remain on the stone.

фигурки из селенита

Selenite figurine

For details on how to take care of such souvenirs, see the article on selenite.

Buy

The price of building mixtures with gypsum is democratic. The cost of a kilogram starts from 5 rubles / kg.

Buy souvenir products made of selenite or alabaster will cost more. For example, the "Bag of Good" will cost 163 rubles.

This mineral is familiar to everyone. Collectors strive to pick up a full range of gypsum stones, which is not easy. Some of its varieties are equal in rarity with semi-precious gems.

гипс минерал

What is gypsum

For most, gypsum is a dense, opaque, grayish substance that is applied to a broken arm or leg in the hospital.

However, the description of the natural mineral is richer:

  • It can be half or completely transparent, translucent, even luminous.
  • Luster - pearlescent, glassy, ​​silky, matte.
  • More often presented as a tabular agglomerate or crystals - columns, prisms, needles.

The mineral cannot be dissolved by most acids, but water is no problem.

This characteristic of gypsum is unique: water solubility is maximum at 37.8 °, after which it tends to zero.

Story

The first written records of gypsum date back to 315 AD. It was discovered, studied and proposed by the name of the ancient Greek naturalist and philosopher Theophrastus.

Already in those days, the rock-forming mineral was used as a fertilizer and neutralizer of soil salinity.

The most famous surviving objects are the city walls of the snow-white shining plaster of the city of Risaf (Syria) and the pyramid of Pharaoh Khafre in Egypt.

Physicochemical characteristics

According to the chemical nomenclature, gypsum is an aqueous calcium sulfate. The international classification defines sulfates as a class of mineral.

Its composition is complex, the formula is multicomponent.

Formula CaSO4 2H2O
Color White, shades of gray and red
Line color White
Shine Glass to pearlescent
Hardness 1.5-2.0
Cleavage Very perfect
Break Uneven; flexible but not elastic
Density 2.2-2.4 g / cm³
Syngonia Monoclinic
Refractive index 1.52

Place of Birth

Sedimentary origin ensured the ubiquity of the rock on the planet:

  • Russian deposits are concentrated in the North Caucasus, in the vicinity of the Urals, Krasnodar Territory, Tatarstan, Dagestan.
  • The largest suppliers of raw materials to the world market are the USA, Canada, Spain, Iran, Turkey.

Some of the mines are unique. For example, in Oklahoma. This US state has an array of natural gypsum formations - the Alabaster Caves Park with raw materials of white, pink and the rarest black. However, it is mined there in crumbs.

Mineral varieties

Depending on the structure, density, and other characteristics, several varieties of gypsum are distinguished:

  • Alabaster. The whitest mineral of high purity. Among the Greeks, the term αλαβαστρος meant "white." Formed when gypsum is heated to 142 ° C.
  • Selenite. A colorless variety of a fibrous structure with a silky sheen. Found a century and a half ago in the Urals. Named for the radiance, as if emanating from the inside of the stone. By this characteristic, it is easy to distinguish it from other types of gypsum.

In Russia it is known as "Maryino glass". The history of the name is connected with the tradition of covering the faces of saints with transparent selenite plates, especially the Mother of God (Virgin Mary).

  • Desert rose. Plaster of paris in pastel shades, collected in the form of a rosebud. Found in the deserts of Africa.
  • Crystal. Not particularly durable mineral of grayish shades. Goes for souvenirs.
  • Anhydride. Dehydrated gypsum in the form of crystals (sometimes very large). Looks like marble. It is easy to distinguish the origin by placing the sample in a humid microclimate. The gypsum will gradually swell and deform.

    Ангидрид
    Mineral Anhydride

There is a classification of the mineral according to the speed of setting (fast-, medium-, slow-setting gypsum).

Where is used

The scope of application of gypsum is limitless. Each uses the right type of raw material.

Applied spheres

It is an inexpensive practical material for cement, slabs, blocks, cornices. Suitable for inter- or exterior.

применение гипса

Alabaster is important as a raw material in the production of special grades of paper, enamels, paints, glazes, and medical compounds.

The substandard is ground, turning it into a soil desalting agent.

Aesthetics

Sculptors do not work without plaster blanks.

Master stone-cutters carve out small plastic, vases, caskets from stone.

Colorless transparent selenites are especially in demand. Stone cutters turn mysteriously shimmering pebbles into small plastic, an esoteric assortment: pyramids, balls, pendulums.

Браслет с селенитом
Selenite bracelet

Jewelers create cabochons.

However, the fragility of the mineral limits the range. Basically, these are pendants, pendants, brooches - something that does not run the risk of quickly wearing out or crumbling.

Collecting

It is possible to collect the "gypsum section" of a mineralogical collection for years, the manifestations and forms of the mineral are so varied.

Connoisseurs are especially interested in “desert rose”, “Mary's glass”, black and pink stones from America, “dovetail”, samples with the effect of a cat's eye.

марьино стекло
Maryino glass

How to care

Gypsum is strong, but vulnerable, so you need to take care of it carefully:

  • Eliminate falls, impacts, mechanical impact.
  • Protect stones from the harsh sun (especially alabaster, which quickly turns yellow, tarnishes).
  • Do not place products in rooms with consistently high humidity (bath, pool, open veranda, greenhouse).

A humid microclimate is detrimental to gypsum: the mineral is saturated with water, losing its shape and decorativeness.

The dirt is removed from the stone with a dry or slightly damp cloth.

It is useful to recharge the selenite variety of the mineral with the light of the moon, putting it on the windowsill at night.

The cost

In the Russian segment, the Networks offer to buy building and collection materials, miniature plaster products (price, rubles):

  • translucent samples (5-18 cm, Russia) - 560-4 800;
  • "Desert rose" (9x7x3 cm, Namibia) - 1 750
  • figures (5-11 cm, Russia) - 540-1 320.

Collectible stones of unique shapes, sizes, shades are available at completely different prices - tens of thousands of rubles.

Therapeutic effect

The healing properties of gypsum are recognized by lithotherapists and official medicine.

Medical science uses the mineral in the following areas:

  • Treating bone fractures or sprains.
  • Sweating regulation.
  • Cleaning the skin and body in general. No mysticism - this is the merit of calcium and sulfur in the composition of the mineral. It is they who draw out toxins, toxins, unclog pores.

Lithotherapists recommend the mineral to patients with spinal tuberculosis and osteomyelitis. The pebble is applied to any sore spot.

For a physically healthy person, the mineral is suitable as a sedative. Contemplation of a ball or stone for several minutes a day calms, helps to concentrate, overcome apathy, depression, anger.

Magical properties

The magical effect of gypsum is ambiguous:

  • The stone calms the simmering passions. A figurine or mineralogical specimen will suit hot-tempered, nervous people as a sedative.

The magic of gypsum attracts prosperity, love, money to the owner.

  • The crystalline variety of the mineral neutralizes the negative effects of gadgets. The product from it is recommended to be placed near the computer screen.
  • The mineral does not suppress the will of a person, but suggestible, insecure people are not needed: under its influence, these qualities will strengthen.
  • The stone is capable of destroying the Napoleonic plans of proud, vain, stubborn, aggressive persons.

It is advised to put it in the bedroom so that the marriage remains strong.

Plaster of Paris

According to the zodiac, the mineral is suitable for Capricorns, Leo, Sagittarius, Aries. Active, but hot-tempered, superambitious people are often born under these signs. The stone will help them to gain composure, tolerance for others, the ability to listen and hear.

Who among us has not heard the phrase: "Put your leg in a cast!" And some, alas, have experienced this "happiness" - a plaster-cast limb. Why is a limb immobilized with a plaster cast? Gypsum is a pliable material, but it has the property, when interacting with water, to harden and retain the shape that it was given. It is also relatively lightweight.

hand plastering in case of fracture
hand plastering in case of fracture

Gypsum is used not only traumatologists for fractures - the range of its application is very wide, and recently the production of gypsum has been growing at a high rate. In addition to surgeons, plaster is constantly used by dentists ( prosthetists ).

Plaster jaw casts
Plaster jaw casts

This is one of the most cheap materials that were used in ancient Egyptian times: for plastering , production bricks and whole building blocks, manufacturing stucco decorations и facing tiles .

Gypsum is still quite intensively used in construction, and although new materials have recently appeared, it has not lost its relevance. And he owes this to his properties: excellent resistance to water and fire and excellent thermal insulation qualities. In addition, gypsum blocks are very easy to handle, sawn and nailed.

Also from gypsum they produce well-known plaster , adding to it a certain amount of cement and some other constituents.

Plaster
Plaster

We often see whole gypsum cities on the stage and when watching our favorite films, because scenery for films and performances are usually made of plaster.

Sculptors love this pliable stuff too!

Sculpture
Sculpture

So what is gypsum?

Gypsum is a sedimentary mineral - it is calcium sulfate mixed with water. Selenite и alabaster - this is also a variety of gypsum (translucent fibrous is selenite, and granular with a special shine is alabaster).

Selenite is used for making inexpensive jewelry. Alabaster has been used since ancient times to grind interior items - countertops, vases, etc.

Gypsum
Gypsum

Gypsum is a good fertilizer and is used in agriculture.

The pulp and paper industry also uses gypsum.

In the chemical industry, using gypsum, enamel, paints, glaze are obtained.

Where does gypsum come from? It is mined from thick layers buried underground, which can occur at completely different depths and have different lengths. Gypsum is found almost everywhere in the world - somewhere more, somewhere less. In Texas, for example, gypsum layers of incredible thickness were discovered - more than 100 meters deep and hundreds of square kilometers in area!

Gypsum deposits
Gypsum deposits

The Russian land is also rich in gypsum deposits - Volgograd, Tula, Samara, Nizhny Novgorod regions, Krasnodar and Perm regions, etc.

Maryino glass Из чего сделаны Кремлёвские звёзды

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