In the construction industry, gypsum is in second place after cement-sand mixtures. The unpretentiousness of the material, excellent environmental friendliness and relatively simple technology of use have led to the massive use of building gypsum for the production of safe blocks, decoration elements and even interior items.

Gypsum mass production

The raw materials for the production of gypsum for construction purposes are natural deposits of gypsum stone in the form of anhydrous anhydride - calcium sulfate, its two-water modification CaSO 4 * H 2 O, as well as a huge amount of industrial waste from the chemical and metallurgical production sectors.

Gypsum production technology consists of three successive operations:

• Purification, fractionation and preliminary grinding of raw materials;
• Heat treatment at different temperatures, from 160 o C to 1000 o C;
• Final regrinding of the heat-treated gypsum mass to a dusty state, drying and packaging of the building material in sealed packaging.

The general technology for the production of gypsum divides the gypsum binder into two categories - quickly setting, or semi-aqueous material, and slowly setting gypsum stone. The first group includes building and high-strength molding gypsum material, the second group includes less durable anhydride cement and high-fired stone, called in the old fashioned way estrich gypsum.

In the process of heating to 180 ° C, the raw material - two-water gypsum stone breaks down into two modifications, after separation on sieves, high-strength α-gypsum is used to make gypsum stone, blocks and molds, β-modification is divided into several categories, the most viscous, with high bending strength, used for construction purposes, the rest as a decorative and auxiliary material.

Varieties of gypsum stone

In addition to the chemical composition, the properties and characteristics of gypsum largely depend on the structure of the raw material. For example, in addition to natural alabaster stone, which has a pronounced polycrystalline structure, a fibrous variety of calcium anhydride, selenite, is used for production.

All varieties of gypsum, from building to decorative or architectural, are obtained by varying the content of selenite, alabaster, raw gypsum stone, finely ground waste of calcium sulfate, heat-treated at different temperatures. After fractionation of the raw material according to the degree of grinding, the gypsum is divided into three groups:

• A - fast-hardening or alabaster materials;
• B and C - mixtures with a hardening time of up to 15 minutes;
• G - building gypsum materials.

The finer the grain, the faster the material hardens.

Construction or high quality gypsum

For construction work, not the most durable grades of gypsum are used; the uniformity of solidification and relatively large water absorption, which provides mixtures with high plasticity, are considered more important. For the production of building materials from gypsum, putties, gypsum plaster mixtures, the β-modification of the average fineness of grinding is used.

Due to special wetting and setting retarding additives, gypsum mortar can be worked almost like a cement-sand mixture. This reduces the shrinkage of the gypsum and the risk of cracks in the building material.

High strength gypsum stone

Finely milled α-modifications of raw gypsum are used for the manufacture of prefabricated building finishing elements, such as artificial facing stone, gypsum boards, fire barriers and flooring slabs.

High-strength gypsum mixes can be used for finishing the walls of frame buildings, ceilings, and interior details. For 100 kg of heat-treated raw mass, there is no more than 20% of the high-strength fraction, so the material is quite expensive and is rarely used in its pure form. Most often, high-strength building gypsum is the basis for the manufacture of fire-resistant or architectural material.

Polymer stone-gypsum

The idea of ​​adding polymer additives to the gypsum mass has been used for a long time. Get polymer gypsum in two ways:

• The addition of water-soluble polymer compounds that improve the fluidity of gypsum and the wetting of the grain. A water-soluble polymer, for example, a polyvinyl acetate emulsion or an aqueous solution of carboxycellulose, increases the material's resistance to impact and alternating loads;
• Saturation of the surface of the finished casting from building gypsum with volatile polymer compositions, most often based on polyurethane or polypropylene.

In both cases, a thin plate of building gypsum turns out to be quite elastic and at the same time light. From polymer gypsum, you can easily make an inexpensive finish that imitates expensive wood species in texture and pattern.

cellacast gypsum material

The widespread use of gypsum material is hindered by one of its inherent shortcomings - the high fragility of gypsum. This prevents the production of thin screeds or shells from building gypsum. Therefore, the building material is saturated with a special reinforcing microfiber, the surface of which is treated with polyurethane.

As a result, the strength of the building material increases by 40-50%, and the resistance to bending loads by 150-200%. Celacast plaster is widely used in medical institutions for applying fixing dressings for fractures and severe injuries of the extremities.

Sculptural or molding plaster material

Ordinary building gypsum, after a slight modification with polymer resins and dihydric alcohol, turns into a mass from which you can make a model, impression, bas-relief of any complexity.

Gypsum molding material must not be diluted with water, as is usually done for building gypsum. In the kit, a special solvent on a water-alcohol basis is attached to a white or beige-gray finely ground powder. Due to the use of a solvent, it is possible to achieve almost zero shrinkage of the material. Therefore, souvenir products and casts from objects with the smallest carving or engraving are often made from sculptural plaster, for example, when copying rare coins, artifacts, old awards.

Acrylic gypsum block

Building gypsum is quite simple to turn into a homemade version of homemade faience. It is enough to carry out the kneading with the preliminary addition of one-component acrylic resin. The result is a light and very hard casting, which can be processed by carving, grinding, drilling. For example, make decorative stucco molding or vases for antique porcelain out of building plaster.

In the construction industry, mixtures of acrylic and gypsum are used for the manufacture of wall cladding from gypsum blocks and the formation of a rough base for self-leveling self-leveling floors.

Polyurethane gypsum material

The use of non-woven polyurethane fabrics and fibers with a specially treated surface made it possible to create a fundamentally new material for the manufacture of immobilizing dressings, tourniquets and pads that fix limbs and body parts in case of severe injuries.

Unlike cellocast gypsum, polyurethane gypsum material has high strength and sufficient casting flexibility to reduce discomfort from its use. Polyurethane material is obtained from building materials using a special procedure for reseeding the ground mass and isolating the largest grain of the same size. As a result of the processing of the rough mass of building gypsum, a casting with huge pores is obtained, providing free access of air to the tissues of the body.

White gypsum stone

Building gypsum serves as a raw material for the manufacture of so-called white or dental gypsum materials. The white color is obtained due to the deep purification of the feedstock, sulfur oxides, sulfates of heavy metals, iron, and organic impurities are removed, which usually stain the building gypsum in a grayish-beige color.

From white finely ground stone, mixtures are made for molding impressions necessary for subsequent prosthetics or treatment. White stone differs from building material in a whole bunch of additional qualities:

• The composition of the gypsum casting must not contain irritating or toxic materials;
• No shrinkage of the white plaster mold;
• Minimum water absorption;
• Rapid setting of the gypsum matrix.

Note! White gypsum typically provides very high impression characteristics, so it is often used to make molds for jewelry. Parts weighing at least 3 g in size are poured into a form of building gypsum.

Fine-grained gypsum

Reducing the grain size of building gypsum can significantly improve its two main characteristics:

• The strength of the material increases under the influence of bending loads;
• Higher flexibility of castings of small thickness.

Casting based on α-gypsum grains of fine grinding is capable of showing a strength of 350-400 kg/cm 2 . The only limitation to be reckoned with is high shrinkage, which is why fine-grained building gypsum is used for repair work and the manufacture of high-strength coatings.

Note! From fine-grained gypsum, after evacuation and high-temperature curing of the mixture, it is easy to make a thin sheet, which is almost identical in appearance and properties to packaging cardboard.

liquid gypsum material

If alcohol glycol solutions are used instead of water for mixing building gypsum, then the material can be stored unchanged for a long time. Liquid gypsum material is used to perform repair and thermal insulation work. After adding an aqueous solution of calcium chloride and sodium chloride, liquid gypsum can be pumped under pressure into cracks in walls or floor slabs. To repair the foundation, the liquid is used only in combination with polymer resins, for example, polyurethanes.

Waterproof gypsum stone

For all its merits, ordinary building gypsum remains quite sensitive to moisture or condensation. Moisture-resistant material GKVL is made using thermosetting polymer powders, and sometimes just finely divided polystyrene, added to dry building gypsum at the stage of plate molding.

After curing, the building boards are subjected to heat treatment, and the material acquires water-resistant qualities.

Refractory block

A heat-resistant or even refractory gypsum block on an industrial scale is made on the basis of conventional building gypsum and fire-resistant additives. Such material can even be made with your own hands according to the following recipe:

• 30% by weight of high-quality building gypsum and the same amount of water;
• 15% ground ash or fireclay dust;
• 4% alumina, you can take washed skinny white clay;
• 2% quicklime and ground iron dioxide.

Note! If building gypsum is needed according to fire safety class G1, then a complex composition can be replaced with finely ground quartz sand, however, such a gypsum stone will not withstand heating above 600 ° C.

Architectural

Most often, building gypsum for architectural work means ordinary molding gypsum modified with polyurethane fibers or polystyrene. This is a relatively soft material, and you can easily make a model or cast the simplest elements of stucco molding from it without any problems.

Real architectural gypsum for construction work is made on the basis of gypsum stone, fired at a temperature of 800-1000 ° C. It turns out a very hard, viscous building gypsum that does not absorb water well. If you withstand the technology of preparing the batch, you will get a gypsum casting with a very hard and at the same time wear-resistant surface.

Unlike polystyrene architectural plaster, from which craftsmen now like to assemble decoration in the style of the 17th century, real stucco for exterior walls was cast from highly fired building plaster. The difference is impressive. Polystyrene stone stands at most 10 years, old red-hot gypsum in the climate of St. Petersburg withstood almost two hundred years.

Grades of gypsum mixtures

In the production process, the heat-treated mass after grinding is fractionated according to the density and particle size. In accordance with GOST No. 125-79, the material is divided into four groups or twelve grades.

The first group includes ordinary gypsum materials G2-G7, with a strength of 20-70 kg / cm 2, the second group - low-shrink mixtures G10, G13-16. The third group is high-strength G22-25, the fourth includes gypsum mixtures with special properties, for example, fire-resistant or highly porous blocks and stones.

Building plaster properties

An ordinary gypsum block used for building purposes is a highly porous mass, the volume of air channels can reach 50-55%. The density of building gypsum stone is 2.6-2.75 g/cm 3 , for a bulk mass of 900-1000 kg/m 3 in a pressed but uncured state, the building mixture can be compacted up to 1400 kg/m 3 .

Dry solid gypsum stone easily withstands heating up to 450-500 ° C, after 100-120 minutes after the onset of thermal exposure, the surface begins to peel off until gradual destruction. The thermal conductivity of the gypsum block is 0.259 kcal/m deg/hour at room temperature.

Grinding degree

Raw building gypsum obtained in the process of processing with superheated steam under a pressure of 1.5-2.5 atm is conditionally divided into three grades

• The first grade of material corresponds to the fraction that leaves on a sieve with an opening density of 918 units. per cm 2 no more than 15% of the initial volume. This is the most active and durable fraction of building gypsum;
• To the second grade include more viscous masses with a residual moisture of not more than 0.1% of the mass, after passing the sieve test, no more than 25% should remain on the grid;
• The third grade, building plaster of especially fine grinding, leaves no more than 2% of the mass on the sieve.

It is clear that the finer the calcium anhydride grain, the faster water absorption occurs and the more hydraulic bonds are formed between the individual grains of building gypsum, the stronger and harder the gypsum stone becomes.

Compressive and bending strength

The tensile strength for building gypsum of the first category is defined as 55 kg / cm 2. The second category after the completion of the hardening process must withstand a static load of 40 kg/cm 2 . After about four hours, the hardened building stone after drying must withstand up to 200 kg / cm 2.

The flexural strength for dried stone is 30% of static compression for unreinforced material and 65% for reinforced mass. Increasing the stone's moisture content by as little as 15% can reduce strength by 40-60%.

Normal Density, Water Demand or Water-Gypsum Ratio

The amount of water required to form internal bonds between grains depends on the chemical composition. For hemihydrate-based α-gypsum, 35-38% of water is required by weight of the building gypsum stone, for a weaker viscous β-hemihydrate, from which the bulk of the building gypsum material is made, 50-60% of an aqueous solvent is needed.

The density of the gypsum mixture in the first minutes corresponds to wallpaper glue, after 10 minutes. it is already thick sour cream, and after another 5 minutes. - viscous, crumbling mass. By introducing additives based on FFA, alum gels or even lime, the density can be stabilized, and the total water consumption of the building material can be reduced by 10%.

Reinforcement of gypsum boards and blocks

Despite the internal homogeneity of the hardened gypsum mass, the bending strength of blocks and slabs is considered insufficient. It is especially difficult to work with thin plates and sheets. Often, the fall of building gypsum cladding from the wall to the floor means the destruction and chipping of the material.

Building gypsum blocks are reinforced with chopped polyester fiber, thin-sheet panels are reinforced with the introduction of fiberglass and fluff pulp.

Gypsum as a binder

The dry gypsum mixture has a high water absorption capacity, for example, hemihydrate α-gypsum has a surface area of ​​up to 6000 cm 2 /g, and a weaker β-modification is twice as large. A small amount of 3-5% gypsum mixture added to lime or cement mortar can increase the viscosity by 15%.

A relatively simple and effective way to correct the viscosity of any mortar, but it should be borne in mind that the process of water absorption develops in progression, so the residual viscosity of the mixture will be formed no earlier than 15 minutes after the addition of the material.

Plaster setting

High-quality gypsum has a high hardening rate, in practice, for a freshly fired building material of the first category, the setting process should begin as early as 4 minutes after dilution with water. For gypsum material of the second category, the curing process according to the standard should begin no earlier than after 6 minutes. It is clear that due to the absorption of water vapor from the air, gypsum, even when carefully packed in a waterproof shell, loses activity, therefore, by the standards for gypsum material, the maximum time for the onset of hardening is limited to 30 minutes. Anything more than that is already considered unusable. The total setting time from the start of mixing to the transition to a solid state should not exceed 12 minutes.

The setting time of building gypsum is limited to a period of 3 hours. The exception is anhydride cement, for which the setting time limit is set at 24 hours. - sand mixtures, 28 days. The hardened anhydrite gypsum binder sample must withstand a compressive load of 50-150 kgcm2.

Plaster hardening

The process of binding water and building strength with gypsum may be accompanied by the expansion of the hardening mass. The more anhydride in the chemical composition in soluble form, the greater the degree of expansion. For example, the hemihydrate is able to increase the size by 0.5%, and for the β-modification, the casting material increases by all 0.8%.

This leads to self-hardening of the building mass, but it is not very convenient if you need to maintain the maximum accuracy of the cast, so the effect is combated with the help of 1% lime additives or Pomazkov materials. In the process of drying, building gypsum shrinks, so stone masses of great thickness are always loaded with internal stresses.

Building plaster: application

A high degree of versatility and a very simple preparation technology have become the reason for the huge popularity of gypsum stone. The material is perfectly processed, cut, drilled, glued. At the same time, in the mass of building stone, there are practically no aging and degradation processes, as in plastic or polymer-mineral plates.

Gypsum blocks and plasterboard sheets have become one of the most popular options for wall cladding in residential premises. First, the high porosity of gypsum makes it possible to regulate moisture naturally. Secondly, building gypsum has good sound insulation and low thermal conductivity.

The material is easy to paint and plaster, if necessary, with the help of wax mastic, the walls can be made waterproof to water and condensate, but relatively transparent to water vapor.

Preparing the mixture

The process of preparing a gypsum mortar begins with sifting the dry mixture through a sieve, it is best to use DK0355, this is about 400 holes per square centimeter. Next, the required amount of water is heated to 40 ° C and poured into the mixer container. Gypsum is added in small portions to the water, and then a thin film formed on the water surface is broken with a trowel.

In theory, the strength of the casting of a building gypsum block depends on the consistency of the batch. The thicker the solution, the smaller the size of the pores and anhydride crystals. With an excess of water, the crystals rapidly increase in size, which leads to intense pore formation.

Material storage

The only reliable way to store dry gypsum material well is to use glass jars with a sealed lid. Dry calcined gypsum can be used to drain containers or floors, but to restore the initial qualities, the material must be deoxidized with an aqueous solution of sulfuric acid, removed by calcination of water and re-ground into dust to a grain size of 0.01-0.003 mm. Industrial polyethylene packaging provides reliable storage of the dry mixture only during the first two months. Dry plasters based on gypsum material in paper bags should be used within 3 days after opening.

Gypsum substitute

The only material that can replace building gypsum is considered to be alabaster, both in its pure form and with the addition of lime or polymer emulsions. Dry lime in an amount of up to 1% must be applied at the stage of preparing the building mixture for kneading. The material is intensively rubbed on a metal or stone surface to make the batch as homogeneous as possible. If it is necessary to prepare a mold, then white clay and flake graphite can be added to the alabaster at the rate of 2% and 1%, respectively.

What is the difference between gypsum and alabaster

Both materials are the product of burning natural sulfuric anhydride, but due to the large amount of impurities of iron oxide and aluminum oxide, the alabaster material is obtained with a slight reddish tint. Unlike gypsum, alabaster sets in 3-5 minutes, so any alabaster stone castings have a high surface hardness. Alabaster perceives mechanical loads worse and gives a high degree of expansion with subsequent shrinkage.

The name gypsum comes from the Greek word gipsos - gypsum or chalk. Gypsum is one of the most common minerals in the world. Other names for the mineral and its varieties: silky spar, Ural selenite, gypsum spar, maiden or marino glass.

Gypsum is hydrous calcium sulfate. The color of the mineral is white, pinkish, yellowish-cream.

Place of Birth. In the Arkhangelsk, Vologda and Vladimir regions, in the Western Urals, in Bashkiria (Permian age); in the Irkutsk region, in the North Caucasus, in Dagestan and Central Asia (Jurassic age), in the USA, Canada, Italy, Germany and France.

Genetic classification - Syngony monoclinic.

By origin and presence in nature, gypsum is closely related to anhydride. This is a typical marine chemical sediment. Forms layers among sedimentary rocks, often associated with anhydrite, halite, native sulfur, sometimes oil, can be formed during anhydrite hydration.

Gypsum is also formed in the zone of weathering of sulfides and native sulfur, with the formation of dense or loose masses, usually contaminated with clay and other impurities - the so-called gypsum hats. Like anhydrite, gypsum is found in the products of humoral activity.

Applications. Gypsum is used raw and burnt. When heated to 120-140 degrees, it turns into CaSO4 * 0.5H2O hemihydrate (half-baked gypsum or alabaster), at higher temperatures, calcined gypsum (building gypsum) is obtained.

Calcined gypsum is used for stucco work, in architecture, for plastering, in medicine, in the cement and paper industries. Raw gypsum is used in the production of Portland cement, for sculpting statues, and as a fertilizer. Fibrous gypsum selenite (especially from the Kungur region in the Urals) is widely used for crafts.

Physical properties

a) Thick and thin tabular crystals, sometimes very large; twins are characteristic - dovetail,
b) Aggregates are dense, granular, foliated, fibrous (selenite),
c) The color is white, often transparent, also gray and pink from impurities. line white,
d) Luster is glassy, ​​in fibrous varieties it is silky,
e) Cleavage is very perfect according to (010). By cleavage, you can split off thin leaves,
f) Hardness 2 on the Maos scale, drawn with a fingernail,
g) Density 2.3.

The chemical formula is Ca*2H2O.

Medicinal properties

Promotes the fusion of limbs, the cure of sprains, dislocations and other injuries, the cure of tuberculosis of the spine (gypsum bed), osteomyelitis (fixation of the affected organ). Gypsum powder relieves excessive sweating, gruel from the powder of this mineral, water and vegetable oil is a wonderful tonic mask.

magical properties

Gypsum is known to all of us as an abusive material for copying sculptures by famous masters and as a remedy for healing fractures. But is this the only way to use this mineral? It turns out that gypsum is also a cure for human pride. Gypsum strictly monitors people who are prone to arrogance and a heightened sense of self-worth, creating situations at the energy level when the proud person finds himself in a hopeless situation, for example, with a broken limb. This does not mean that the stone contributes to injury - we get injured because of our own arrogance and carelessness (with the exception of accidents). Gypsum shows the ugliness of human behavior in the most unconventional way - it helps to recover from an injury, without demanding any gratitude or appreciation as a reward.

Gypsum is passive. He does not seek to subjugate the will of a person, tells him how to do the right thing, does not attract the desired success, material well-being, love and good luck.

Gypsum is a valuable stone, and not only as a building material. Millennia ago, people noticed that ground gypsum helps fight soil salinity. By extracting the mineral in karst caves, the ancient miners contributed to the emergence of huge and extended underground spaces. Their compatriots, embedding gypsum in the soil, increased crop yields.

For many peoples, gypsum was the breadwinner. But even entire cities were built of gypsum! Blocks sawn from crystalline gypsum were used to build the walls of the city of Risafa (Syria). The white stone shines dazzlingly in the hot sun even today, when only picturesque ruins remain of the city...

Sculptors all over the world could not work if the world did not have a light, inexpensive and easy-to-use material called gypsum. Gypsum is appreciated by traumatologists, painters, plasterers, and paper manufacturers.

Physical properties of gypsum

The crystals are thick and thin tabular, sometimes very large. The aggregates are dense, granular, foliated, fibrous (selenite). The color of the crystal is white, often transparent, sometimes gray and pink from impurities. The dash is white. The luster is glassy, ​​in fibrous varieties of gypsum it is silky. Hardness 2 on the Mohs scale. Density 2.3 g/cm3.

The chemical formula is Ca(SO4)2H2O.

Origin and deposits

The origin of gypsum is different. In some deposits, a mineral is concentrated that has accumulated as marine sediment, chemically altered during the drying of brine lakes. Elsewhere, gypsum has formed as a result of weathering compounds and deposits of native sulfur - in this case, mineral deposits are often contaminated with clays and rock fragments.
Gypsum deposits are found on all continents. Major Russian developments are being carried out in the Urals and the Caucasus. Gypsum is mined in the mountainous regions of Asia and America (the USA is the champion of gypsum production), in the foothills of the Alps.

Medicinal properties of gypsum

Official medicine widely uses the astringent properties of gypsum. The hygroscopicity of the material allows it to be used as an effective remedy for sweating. Gypsum-oil emulsion is used in medical cosmetology as a substance that restores skin turgor.

Not so long ago, science found out: the crystalline structure of gypsum, as if on purpose, was created to hold heavy metal ions. Lithotherapists responded to the discovery: today, wet wrapping in crushed gypsum is becoming more common. Calcium and sulfur literally pull harmful substances out of the skin and thus gradually heal the body.

Examining a selenite (selenite is a fibrous variety of crystalline gypsum) ball helps to calm the nervous system while concentrating.

The magical properties of gypsum

The main magical property of gypsum is the ability to absorb passions. That is why the possession of plaster decorations is recommended for people who are nervous, quick-tempered, hot. Aries and Capricorns, Lions and Sagittarius can successfully use plaster talismans to optimize their own behavior.

It is difficult to use gypsum crystals in magical rituals: a stone can show a person the vanity of his undertakings, the wretchedness of his goals, and the primitiveness of his actions. The magically destructive role of gypsum is useful for convinced proud and self-confident half-educated people, but it can do a disservice to a person who is not too self-confident.

The use of plaster decorations

In addition to purely practical use, gypsum can be used as an excellent interior decoration. In this case, we are not talking about gypsum stucco, a frequent architectural element of the premises, but about crystalline formations.

"Desert roses" - this is the name of the intergrowths of smoothly curved gypsum plates, really resembling flowers. The similarity is especially strong if the size of the natural aggregate does not exceed the size of a garden rose flower, the color of the plates is white to translucent, and the "petals" themselves are thin, like real petals.

Such specimens are relatively rare and therefore expensive. More often, “desert roses” are nondescript, harvested by hundreds of local collectors, sold by weight ... Nevertheless, even the most modest cream-colored plaster “rose” can become an interior object of admiration and a source of positive aesthetic impressions.

Gypsum crystals in nature can grow to gigantic sizes and at the same time differ in an enviable optical quality. However, gypsum rarely gets cut: the crystalline druze of the mineral is very diverse and very decorative. A collection of gypsum crystals can be collected all your life, but it is unlikely that you will be able to display all forms of natural diversity!

Gypsum in art

Colorless lamellar crystals of gypsum in the Russian language tradition are called "marina glass". The name comes from the past. In the old days, such plaster (especially specimens with a mother-of-pearl tint) was used to frame images. Especially often, transparent or iridescent cast gypsum was used to decorate the icons of the Virgin Mary. Hence the "marino glass".

Fibrous gypsum, found in the Urals in the century before last, immediately became an object of adoration among lovers of elegant knick-knacks. The mineral, as if glowing with an inner light, received the sonorous name "selenite" and became the main material for making figurines. Some varieties of selenite, having the effect of asterism, allow you to carve mystically shimmering sculptural miniatures.

Jewelry made of crystalline gypsum is more of a souvenir character. The fragility of the stone, which is extremely subject to abrasive wear, does not allow cabochons and rings carved from a gypsum monolith to retain their attractiveness for a long time.

Dehydrated gypsum, called anhydrite, resembles marble in appearance and properties. For two centuries, the once popular cabinet writing instruments were also cut from anhydrite. Today, this mineral is used to make sculptural interior decorations.

However, those buyers of anhydrite figurines who place their purchases in greenhouses, winter gardens, swimming pools and other wet rooms are mistaken. In the presence of water, anhydrite absorbs moisture, gradually (not necessarily proportionally) increases in size and loses its decorative effect.

For many people who are inexperienced in repair and construction matters, the question often arises: what is the difference between such building materials as gypsum and alabaster? And why is it written on the top of the bags “gypsum plaster”, and below - “alabaster”?

In order not to get lost in terms, you need to figure out what gypsum and alabaster really are, whether there are differences between them and, if so, what they are.

Gypsum - origin, application

Gypsum is a dry composition made on the basis of a natural mineral - gypsum stone. The mineral is calcium sulfate dihydrate - CaSO4 2H2O with impurities in the form of oxides of silicon, aluminum and iron.

Gypsum is a mineral of sedimentary origin. In nature, it is most often found in the form of elongated prism-shaped crystals, although it sometimes forms in the form of dense tablet or scaly aggregations. The mineral is quite soft, easy to grind.

Large deposits of gypsum stone are located in countries such as Iran, USA, Canada, Turkey, Spain. In Russia, deposits of this rock are located in the Kama and Volga regions, Tatarstan, on the western slopes of the Ural Mountains and in the Krasnodar Territory.

An astringent is obtained from a natural mineral - in fact, the gypsum that we all know. It is a powder of white, cream or grayish color (depending on the impurities present), which, when mixed with water, turns into a plastic mass that hardens quite quickly in air.

The method of using ground gypsum depends on what exactly it is planned to be used for:

• "raw" gypsum is used in medicine to fix fractures, as well as in agriculture - it is scattered in the fields to normalize the acidity of the soil;
• in the form of "building gypsum" it is used during repair and finishing works, for the production of wall slabs and blocks, cornices, stucco moldings.

Also, the mineral is widely used in the paper and chemical industries: in the production of cement, sulfuric acid, glazes and paints.

Natural gypsum is fibrous and granular. For the production of alabaster, fine-grained gypsum is used - alabaster. Construction alabaster has a finer grinding and is the same calcium sulfate, but not dihydrate, but semi-hydrous - CaSO4 0.5H2O. It is obtained by roasting crushed natural alabaster at temperatures up to 180 degrees.

Thus, the alabaster that we purchase in a hardware store is, in a broad sense, gypsum, but not every gypsum can be called alabaster.

Building gypsum has the following characteristics:

• Density (true) is 2.6 - 2.76 g / cu. cm. At the same time, in a loose-filled form, the density is 0.85 - 1.15 g / cu. cm, and in compacted - 1, 245 - 1.455 g / cu. cm.
• Gypsum products have high fire resistance - they are destroyed only after 6-8 hours of exposure to high temperature. Designs withstand heating up to 600-700 degrees without destruction.
• The compressive strength of building gypsum is 4-6 MPa, high-strength gypsum - 15-40 MPa.
• Gypsum and products made from it do not conduct heat well, its heat transfer coefficient in the temperature range from 15 to 45 degrees is only 0.259 kcal/m deg/hour.
• Drying speed. After mixing with water, the gypsum mortar begins to set after 4 minutes and within the next half hour it completely hardens. Therefore, you need to work with such a solution very quickly.

Grades and properties of building gypsum

The normative document regulating the properties and quality of building gypsum binders is GOST 125-79. The industry produces 12 brands of alabaster, differing in compressive fracture strength.

The indicators are shown in the table:

Gypsum brand	Tensile strength of beam specimens 40 × 40 × 160 mm in size at the age of 2 hours,MPa, not less
	compression	bend
G-2	2	1,2
G-3	3	1,8
G-4	4	2,0
G-5	5	2,5
G-6	6	3,0
G-7	7	3,5
G-10	10	4,5
G-13	13	5,5
G-16	16	6,0
G-19	19	6,5
G-22	22	7,0
G-25	25	8,0

An important indicator is the setting time of the binder.

Depending on it, the following types of building gypsum are distinguished:

• A - fast-hardening (beginning no earlier than 2 minutes, end - no later than 15 minutes).
• B - normally hardening (setting begins no earlier than 6 minutes, end - no later than 30 minutes).
• B - slowly hardening (the beginning of setting is not earlier than 20 minutes, the end is not standardized).

The degree of grinding is also normalized:

Thus, according to the brand of binder, all its main characteristics can be determined.

For example, the bag says: Г-6 В II.

This means that we have a material with the following characteristics:

• strength not less than 6 and not more than 7 MPa;
• slowly hardening;
• medium grind.

Varieties of gypsum

Gypsum binders are used not only in pure form, but also with various additives that allow changing their properties.

Currently on sale you can find gypsum of the following varieties:

• Construction - for the production of gypsum building materials and for plastering work. Such material is good because it does not form cracks when dried. Lime is often added to it, which gives the mixture plasticity. The material is mainly used for interior decoration of dry rooms.
• High-strength - a binder with large crystals, providing the final product with less porosity and, accordingly, greater strength. This material is used for the construction of fireproof partitions, molds for the production of faience and porcelain sanitary ware. It is also used in traumatology and dentistry.
• Polymer gypsum is a binder with the addition of polymers. Often used in traumatology. Dressings with such gypsum are much lighter than ordinary gypsum ones, allow the skin to breathe, are not afraid of moisture, are permeable to X-rays (they allow you to control the process of bone fusion).

• Sculptural - the most high-strength gypsum, practically free of impurities. The material has a high degree of whiteness and is used to make figurines. Sculptures, souvenirs, as well as in the automotive and aviation industries. This binder is the basis of dry putty mixtures.
• Acrylic gypsum - obtained by adding water-soluble acrylic resin to the binder. Externally, it is practically indistinguishable from ordinary gypsum, but much lighter. Because of this, it is often used for ceiling moldings. The material is frost-resistant and has low water absorption, therefore it can be used for work on building facades.

Thus, alabaster is one of the varieties of gypsum, which is mainly used in construction. It has greater hardness than natural gypsum, but is less widely used.

Gypsum- mineral, aqueous calcium sulfate. The fibrous variety of gypsum is called selenite, and the granular variety is called alabaster. One of the most common minerals; the term is also used to refer to the rocks he composed. Gypsum is also commonly called a building material obtained by partial dehydration and grinding of the mineral. The name comes from the Greek. gypsos, which in ancient times meant both gypsum itself and chalk. A dense, snow-white, cream, or pink, fine-grained variety of gypsum is known as alabaster.

1. Structure
2. Properties
3. Morphology
4. Origin
5. Application
6. Classification
7. Physical properties
8. Optical properties
9. Crystallographic properties

STRUCTURE

The chemical composition is Ca × 2H2O. The syngony is monoclinic. The crystal structure is layered; two sheets of 2- anionic groups, closely associated with Ca2+ ions, form double layers oriented along the (010) plane. H2O molecules occupy spaces between these double layers. This easily explains the very perfect cleavage characteristic of gypsum. Each calcium ion is surrounded by six oxygen ions belonging to the SO4 groups and two water molecules. Each water molecule binds a Ca ion to one oxygen ion in the same double layer and to another oxygen ion in the adjacent layer.

PROPERTIES

The color is very different, but usually white, gray, yellow, pink, etc. Pure transparent crystals are colorless. Impurities can be dyed in different colors. The dash color is white. The luster of the crystals is glassy, ​​sometimes with a mother-of-pearl tint due to microcracks of perfect cleavage; selenite is silky. Hardness 2 (standard on the Mohs scale). Cleavage is very perfect in one direction. Thin crystals and cleavage plates are flexible. Density 2.31 - 2.33 g/cm3.
It has significant solubility in water. A remarkable feature of gypsum is the fact that its solubility reaches a maximum at 37-38°C with increasing temperature, and then drops rather quickly. The greatest decrease in solubility is established at temperatures above 107° due to the formation of a "hemihydrate" - CaSO4 × 1/2H2O.
At 107°C, it partially loses water, turning into a white powder of alabaster, (2CaSO4 × H2O), which is noticeably soluble in water. Due to the smaller number of hydrate molecules, alabaster does not shrink during polymerization (increases in volume by approx. 1%). Under p. tr. loses water, splits and fuses into white enamel. On charcoal in a reducing flame it gives CaS. It dissolves much better in water acidified with H2SO4 than in pure water. However, when the concentration of H2SO4 is over 75 g/l. solubility drops sharply. Very slightly soluble in HCl.

MORPHOLOGY

Due to the predominant development of (010) faces, crystals have a tabular, rarely columnar, or prismatic appearance. Of the prisms, (110) and (111) are the most common, sometimes (120) and others. Faces (110) and (010) often have vertical shading. Intergrowth twins are frequent and are of two types: 1) Gallic according to (100) and 2) Parisian according to (101). It is not always easy to tell them apart. Both of them resemble a dovetail. Gallic twins are characterized by the fact that the edges of the prism m (110) are parallel to the twin plane, and the edges of the prism l (111) form a reentrant angle, while in the Parisian twins the edges of the prism Ι (111) are parallel to the twin seam.
It occurs in the form of colorless or white crystals and their intergrowths, sometimes colored by inclusions and impurities captured by them during growth in brown, blue, yellow or red tones. Intergrowths in the form of a “rose” and twins are characteristic - the so-called. "dovetails"). It forms veinlets of a parallel fibrous structure (selenite) in clayey sedimentary rocks, as well as dense continuous fine-grained aggregates resembling marble (alabaster). Sometimes in the form of earthy aggregates and cryptocrystalline masses. It also forms the cement of sandstones.
Common are pseudomorphs after gypsum of calcite, aragonite, malachite, quartz, etc., as well as pseudomorphs of gypsum after other minerals.

ORIGIN

A widely distributed mineral, it is formed in natural conditions in various ways. Sedimentary origin (typical marine chemogenic sediment), low-temperature hydrothermal, found in karst caves and solfataras. It precipitates from sulfate-rich aqueous solutions during the drying of sea lagoons and salt lakes. Forms layers, layers and lenses among sedimentary rocks, often in association with anhydrite, halite, celestite, native sulfur, sometimes with bitumen and oil. In significant masses, it is deposited by sedimentation in lacustrine and marine salt-bearing dying basins. In this case, gypsum, along with NaCl, can be released only in the initial stages of evaporation, when the concentration of other dissolved salts is not yet high. Upon reaching a certain value of the concentration of salts, in particular NaCl and especially MgCl2, anhydrite will crystallize instead of gypsum and then other, more soluble salts, i.e. the gypsum in these basins must belong to the earlier chemical sediments. Indeed, in many salt deposits, layers of gypsum (as well as anhydrite), interbedded with layers of rock salt, are located in the lower parts of the deposits and in some cases are underlain only by chemically precipitated limestones.

In Russia, thick gypsum-bearing strata of Permian age are distributed in the Western Urals, in Bashkiria and Tatarstan, in Arkhangelsk, Vologda, Gorky and other regions. Numerous deposits of the Upper Jurassic age are established in the North. Caucasus, Dagestan. Remarkable collection specimens with gypsum crystals are known from the Gaurdak deposit (Turkmenistan) and other deposits in Central Asia (in Tajikistan and Uzbekistan), in the Middle Volga region, in the Jurassic clays of the Kaluga region. In the thermal caves of Naica Mine, (Mexico), druze of gypsum crystals of unique size up to 11 m long were found.

APPLICATION

Today, the mineral "gypsum" is the main raw material for the production of α-gypsum and β-gypsum. β-gypsum (CaSO4 0.5H2O) is a powdered binder material obtained by heat treatment of natural two-water gypsum CaSO4 2H2O at a temperature of 150-180 degrees in apparatus communicating with the atmosphere. The product of grinding β-modification gypsum into a fine powder is called building gypsum or alabaster, with finer grinding, molding gypsum is obtained or, when raw materials of increased purity are used, medical gypsum.

During low-temperature (95-100 °C) heat treatment in hermetically sealed apparatus, α-modification gypsum is formed, the grinding product of which is called high-strength gypsum.

In a mixture with water, α and β-gypsum hardens, turning back into dihydrate gypsum, with heat release and a slight increase in volume (approximately 1%), however, such a secondary gypsum stone already has a uniform fine-crystalline structure, the color of various shades of white (depending on raw materials), opaque and microporous. These properties of gypsum are used in various fields of human activity.

Gypsum (eng. Gypsum) - CaSO4 * 2H2O

CLASSIFICATION

Strunz (8th edition)	6/C.22-20
Nickel-Strunz (10th edition)	7.CD.40
Dana (7th edition)	29.6.3.1
Dana (8th edition)	29.6.3.1
Hey's CIM Ref.	25.4.3

PHYSICAL PROPERTIES

Mineral color	colorless turning into white, often colored by minerals-impurities in yellow, pink, red, brown, etc.; sometimes there is a sectorial-zonal color or distribution of inclusions over growth zones inside the crystals; colorless in internal reflexes and through.
Dash color	white
Transparency	transparent, translucent, opaque
Shine	glassy, ​​close to glassy, ​​silky, pearlescent, dull
Cleavage	very perfect, easily obtained from (010), almost mica-like in some samples; according to (100) clear, turning into conchoidal fracture; by (011), gives a splintery fracture (001)
Hardness (Mohs scale)	2
kink	smooth, conchoidal
Strength	flexible
Density (measured)	2.312 - 2.322 g/cm3
Radioactivity (GRapi)	0

OPTICAL PROPERTIES

CRYSTALLOGRAPHIC PROPERTIES

Gypsum is one of the most common minerals in the world. It is mined from the bowels of the earth everywhere and is widely used in industry, the construction industry, and medicine. In our article you will find a detailed description and photo of the gypsum mineral. In addition, you will learn about the main areas of its application.

Mineral gypsum: description and chemical composition

The name of the mineral, rock, as well as the corresponding building material comes from the Greek word gipsos ("chalk"). Humanity has known about gypsum since ancient times. It has not lost its popularity even today.

Gypsum is a soft mineral. By the way, it is a reference for the Mohs scale of relative hardness, adopted at the beginning of the 19th century (hardness - 1.5-2.0).

According to the chemical composition, the mineral gypsum is an aqueous calcium sulfate. Its structure includes elements such as calcium (Ca), sulfur (S) and oxygen (O). Let's describe the chemical composition of gypsum in more detail:

• sulfur trioxide, SO3 - 46%;
• calcium oxide, CaO - 33%;
• water, H2O - 21%.

Genetic classification: monoclinic syngony. This mineral is distinguished by a layered crystalline structure and a very perfect cleavage (single thin “petals” can be easily split off from it).

Mineral gypsum: properties and distinguishing features

Here are the main physical characteristics of gypsum by which it can be distinguished from other minerals:

• the fracture is uneven but flexible;
• gloss: from glass to silky or matte;
• hardness: low (easily scratched with a fingernail);
• the mineral slowly dissolves in water;
• not greasy to the touch;
• leaves behind a clearly visible white line;
• color: from white to gray (sometimes it can be pink).

Gypsum does not react with acids, but dissolves in hydrogen chloride (HCl). It can have different transparency, although the transparent mineral gypsum is more common in nature. When heated above 107 degrees Celsius, gypsum turns into alabaster, which, in turn, hardens when wetted with water.

Gypsum is often confused with anhydrite. These two minerals can be distinguished from each other by hardness (the second is much harder than the first).

The genesis of the mineral and its distribution in nature

Gypsum is a typical mineral of sedimentary origin. Most often, it is formed from natural aqueous solutions (for example, at the bottom of drying seas and reservoirs). The mineral gypsum can also accumulate in weathering zones of native sulfur and sulfides. In this case, the so-called gypsum hats are formed - loose or compacted rock masses contaminated with numerous impurities.

Gypsum is often found in sedimentary rocks, accompanied by sand, rock salt, anhydrite, sulfur, limestone, and iron. Neighborhood with the latter, as a rule, gives it a brownish tint.

In nature, gypsum occurs in the form of elongated and prismatic crystals. It also often forms dense, scaly, fibrous, or "tablet" aggregations. Often gypsum is presented in the form of so-called roses or swallowtails.

The main varieties of the mineral

Geologists distinguish several dozen varieties of gypsum. The mineral can be fibrous, satiny, dense, foamy, fine-grained, boney, cubic, etc.

The main varieties of gypsum include:

• selenite;
• alabaster;
• "marino glass".

Selenite is a translucent mineral with a silky sheen. The name comes from the Greek word selena - "moon". This mineral is indeed distinguished by a slightly bluish tint. Selenite is used as an ornamental stone in the manufacture of budget jewelry.

Alabaster is a soft, easily destructible white material, a product of gypsum dehydration. It is widely used in the production of garden sculptures, vases, countertops, moldings and other interior items.

"Maryino glass" (girl's or ladies' ice) is another type of gypsum, a transparent mineral with a mother-of-pearl or colored tint. It has a unique crystal lattice structure. In the old days, "Maryino glass" was widely used in the design of icons and holy images.

The main deposits of gypsum

The mineral gypsum is ubiquitous in the earth's crust. Its deposits are found in deposits of almost all periods of the geological history of the planet - from the Cambrian to the Quaternary. Deposits of gypsum (as well as its accompanying anhydrite) in sedimentary rocks are in the form of lenses or layers with a thickness of 20-30 meters.

Every year, over 100 million tons of gypsum are extracted from the bowels of the earth. The world's largest producers of valuable building materials are the USA, Iran, Canada, Turkey and Spain.

In Russia, the main deposits of this rock are concentrated on the western slopes of the Ural Mountains, in the Volga and Kama regions, Tatarstan and the Krasnodar Territory. The main gypsum deposits in the country are Pavlovskoye, Novomoskovskoye, Skuratovskoye, Baskunchakskoye, Lazinskoye and Bolohovskoye.

Applications of gypsum

The scope of gypsum is extremely wide: construction, medicine, repair and decoration, agriculture, chemical industry.

Since ancient times, sculptures and various interior items have been carved from this mineral - vases, countertops, balustrades, bas-reliefs, etc. Cornices, wall blocks and slabs (the so-called drywall) are often made from it. In its "raw" form, gypsum is also used in agriculture as a fertilizer. It is scattered on fields and lands to normalize the acidity of the soil.

Where else is gypsum used? The mineral is widely used in the paper and chemical industries to produce cement, sulfuric acid, paints and glazes. In addition, anyone who has ever broken a leg or arm is familiar with another area of ​​​​its application - medicine.

Gypsum as a building material

Building material gypsum is obtained from gypsum stone. To do this, the rock is burned in special furnaces, and then ground into a fine powder. In the future, the resulting raw material is widely used in construction and decoration.

The industrial industry has its own classification of gypsum - technical. So, the following varieties are distinguished:

• high-strength gypsum (used in medicine and dentistry; various building mixtures and molds for the porcelain-faience industry are also produced from it);
• polymeric (used exclusively in traumatology for applying fixing bandages for fractures);
• sculptural (the name speaks for itself - it is the main component of putty mixtures, various figurines and souvenirs);
• acrylic (lightweight gypsum used for finishing the facades of buildings);
• refractory (non-combustible material, from which plasterboard sheets and wall blocks are often produced).

In addition, there is a separate marking of gypsum for strength. According to it, 12 grades of gypsum are allocated - from G2 to G25.

Alabaster is also widely used in construction and finishing works. Compared to gypsum, it is more durable and easier to work with. True, without special additives, alabaster is practically unsuitable, since it dries out instantly.

It is important to note that even with the modern, such a high level of development of science and industry, a worthy replacement for gypsum has not yet been found.

Healing and magical properties of the stone

Gypsum is not in vain used in medicine. It promotes the fusion of bone tissue, relieves excessive sweating, and cures tuberculosis of the spine. Gypsum is also used in cosmetology - as one of the components of tonic masks.

Since ancient times, this mineral was considered a kind of "cure" for human pride, arrogance and excessive arrogance. In magic, it is believed that gypsum is able to tell a person what he needs to do in a given situation. It promises good luck and material well-being. Astrologers advise people born under the signs of Capricorn, Aries and Leo to wear plaster amulets.

"Desert Rose" - what is it?

Such a beautiful name is called a mineral aggregate, one of the varieties of gypsum. It really does look like flower buds. The aggregates consist of crystalline lenticular intergrowths-petals of a characteristic type. The color of the "desert rose" can be very diverse. It is determined by the color of the soil or sand in which it formed.

The mechanism of formation of these "roses" is rather interesting. They are formed in especially arid natural and climatic conditions. When it occasionally rains in the desert, sand instantly absorbs moisture. Water interacts with particles of gypsum, which are washed away with it deep into. Later, the water evaporates, and the gypsum crystallizes in the sandy mass, creating the most unexpected and bizarre forms.

"Desert Rose" is well known to the nomadic tribes of the African Sahara. Some cultures in the region have a tradition of giving these stone flowers to their loved ones on Valentine's Day.