If you wondered what gypsum is, you should know that it is a mineral belonging to the class of sulfates. Two varieties of this material are known, one of which is called fibrous, and the other is called granular. The last one is alabaster.
General information
Gypsum has a silky or vitreous luster, the former of which is characteristic of the fibrous variety. Cleavage is perfect in one direction. The material is split into thin sheets. Color can be:
- reddish;
- grey;
- white;
- brown;
- yellowish.
Fibrous varieties give a splintery fracture. The material density is 2.3g/cm3. The gypsum formula is as follows: CaSO4 2H2O. The texture of the material is massive.
Properties and varieties
The specific gravity of the material can reach 2.4g/cm3. Gypsum is quite dense, it can be granular and foliated, as well as fibrous. Some of its twins resemble a dovetail. It is sometimes confused with anhydride, which has a medium hardness.
When you study the question of what is gypsum,you will find out that when heated, the material turns into CaSO4•1/2•H2O. The temperature limit is 107 °C. When wetted with water, it hardens and seizes, and dissolves in hydrochloric acid.
Today, 3 varieties are known, among them:
- selenite;
- "marino glass";
- alabaster.
The first is parallel needle-shaped and has a silky sheen. Transparent thick sheet is "marino glass". Painted fine-grained can be alabaster.
Application
Selenite, which is fibrous, is used for inexpensive jewelry. But the large ones are based on alabaster, which has been used since ancient times. The raw material is churned out. As a result, you can also get interior items, including:
- inkwells;
- countertops;
- vases.
If you are interested in the question of what gypsum is, then you should know: the material is used in its raw form as a fertilizer, as well as to obtain glazes, enamels and paints in industry and the pulp and paper industry.
The fired material is used for casts and castings. It can be cornices and bas-reliefs. In medicine and construction, the material acts as a binder. More dense varieties serve as ornamental material.
Additional information about the application
Gypsum is a valuable stone and is widely used in construction. Millennia ago, it was noted thatin the form of a hammer, it helps to fight soil salinization. This mineral was mined in karst caves. From ancient times to this day, gypsum has been applied to the soil to increase crop yields.
For many nations, he was the breadwinner. Entire cities were built from plaster. Crystal blocks were sawn out of it, which went to the construction of walls. The white stone shines dazzlingly in the sun. This can be seen even today, when only ruins remain of the ancient cities.
Sculptors all over the world cannot do without this mineral. It is inexpensive, weighs little and is easy to handle. Appreciated by painters, plasterers, traumatologists and papermakers.
Origin
If you are trying to understand what gypsum is, then you should also familiarize yourself with its origin. This mineral has several types, the method of formation of which is different. In some deposits, a mineral is mined, which was concentrated there in the process of accumulation of marine sediment. In other cases, gypsum was formed when various lakes dried up. The mineral could have arisen from the deposition of native sulfur and from the weathering of its compounds. Deposits in this case may be contaminated with rock fragments and clays.
Deposits
After reading the description of gypsum, you should also learn about the main deposits that are found on all continents. Russian developments are carried out mainly in the territories of the Caucasus and the Urals. The mineral is mined in the mountainous regions of America and Asia. The United States is the plaster championproduction. There are also deposits in the foothills of the Alps.
Specifications
The described mineral has a fairly dense fine-grained structure. In a loose bulk form, the density can vary from 850 to 1150 kg/cm3. When compacted, this parameter reaches 1455 kg/cm3. Getting acquainted with the description of gypsum, you will pay attention to one of its advantages, which is expressed in rapid hardening and setting. At the fourth minute after mixing the solution, the first stage of drying begins, and after half an hour the material hardens.
Ready-made gypsum mortar requires immediate consumption. To slow down the setting, water-soluble animal glue is added to the ingredients. Among the properties of gypsum, the melting point should be distinguished. The material can be heated up to 700 °C without destruction. Gypsum products are quite fire resistant. They begin to break down only 6 hours after being exposed to high temperatures.
The strength of gypsum is also often taken into account. During compression, this parameter can vary from 4 to 6 MPa. If we are talking about high-strength material, then it reaches 40 MPa and may even exceed this value. In well-dried samples, the strength is 3 times higher. The mineral complies with state standards 125-79. It has a thermal conductivity, which is equal to 0.259 kcal / mdeg / hour. The temperature range in this case is equal to the limit from 15 to 45 ° C.
White gypsum dissolves in water in small quantities:
- At 0 °C one liter candissolve 2, 256
- If the temperature rises to 15°C, the solubility increases to 2.534g
- This increases to 2.684g at 35°C.
If further heating occurs, the solubility decreases.
Description, scope and properties of building gypsum
If we compare gypsum with other binders, then the first one has a wider area of use. With it, you can save on other components. The construction variety is used in the manufacture of gypsum parts, when carrying out plaster work and the formation of partition boards.
Gypsum mortar must be worked very quickly. The polymerization start time can be from 8 to 25 minutes after mixing the solution. The final value depends on the variety. At the moment of the beginning of hardening, the mineral gains about 40% of the final strength. In this process, white gypsum is not covered with cracks, so it is possible to refuse various aggregates when mixing the solution with a lime composition. The construction variety reduces the labor intensity and costs of work.
Use and properties of high-strength and polymer gypsum
The chemical composition of the high-strength variety is similar to the construction one. However, the latter has smaller crystals. High-strength has coarse particles, therefore it has less porosity and high strength. This material is obtained by heat treatment of gypsum stone under conditionstightness.
The field of use is the manufacture of building mixtures and the construction of fireproof partitions. From a high-strength mineral, molds are made for the production of faience and porcelain products. The polymer type is also called synthetic and is more familiar to orthopedic traumatologists. On its basis, plaster bandages are made for applying bandages for fractures. But the scope of gypsum is not the only advantage, among others it should be highlighted:
- easy overlay;
- moisture resistance;
- lighter weight than conventional casts.
In closing
Gypsum formula should be known to you if you are interested in this mineral. It is important to take an interest in other properties, as well as varieties. Among others, it is necessary to highlight the molding, sculptural and cellacast.
The latter is used to make bandages, and the structure allows the material to stretch in all directions. The most high-strength is sculptural gypsum, which does not contain impurities. Among the properties of white gypsum, its impeccable whiteness can be distinguished.
