Properties of limestone. Rocks of limestone. Limestone formula

Limestone is a natural natural stone, which is a soft sedimentary rock of organic or organo-chemical origin, consisting mainly of calcium carbonate (calcite). Often its composition includes admixtures of quartz, phosphate, silicon, clay and sand particles, as well as calcareous remains of skeletons of microorganisms. In this article, we will consider in detail this natural material, its types, properties and scope, as well as find out what the chemical formula of limestone is, and much more.

Formation of limestone

First, let's look at how these minerals were formed. Limestone is mainly formed in conditions of shallow shallow basins, although there is also a freshwater one. It is laid in the form of deposits and layers. Sometimes precipitated, like gypsum and salt, from the evaporating water of marine lagoons and lakes. However, most of it was deposited in the seas, which did not experience intensive drying. The formation of most limestone rocks began with the isolation of live calcium carbonate living organisms from sea water to build skeletons and shells. These remains of dead organisms accumulate in large quantities on the seabed. The most vivid example of extraction and accumulation of calcium carbonate are coral reefs. So, in some cases on the fracture of limestone, you can notice separate shells. Under the influence of the sea current and as a result of the impact of waves and surfs, the reefs are destroyed. And on the seabed , calcium carbonate is added to the limestone debris , which precipitates from the water saturated with it. Also in the formation of young rocks limestone is involved calcite, which comes from destroyed ancient rocks.

Varieties

There are many types of limestone. Shell rock is commonly referred to as a conglomeration of shells and their debris cemented into a cellular rock. In the case when the shells are very small, soft, loosely bound, smearing, finely crumbling limestone is formed - chalk. Oolitic rock consists of their miniature, fish-sized eggs, cemented balls. The core of each of them can be represented by a fragment of a shell, a grain of sand or any other particle of a foreign material. In the case when the balls are larger, for example, with a pea, they are usually called pisolites, and the rock, respectively, is pisolite limestone. The next variety is travertine - it forms on the surface when precipitating aragonite or calcite from the waters of carbonic sources. If such deposits have a strongly porous base (spongy), it is called tuff. Uncured mixture of clay and calcium carbonate is called marl.

In addition, limestone can also differ in color. The main color is white. But it can be yellowish, light beige, light gray, rarely - slightly pinkish. White-pink and white-yellow breed are considered the most valuable.

Limestone formula

As mentioned before, this natural material consists mainly of calcite or calcite remains of skeletons and shells, rarely of aragonite. Hence, the limestone formula will have the following form: CaCO ₃ . However, pure rock is extremely rare, in a number of cases it includes various admixtures of quartz, clay minerals, dolomites, gypsum, pyrite and, of course, organic residues. So, dolomitic limestone (the formula of this rock includes MgO) contains from four to seventeen percent of magnesium oxides, marly - up to 21 percent of acid oxides (SiO ₂ + R ₂ O ₃ ). Carbonate composition can include dolomites CaMg (CO ₃ ) ₂ , FeCO ₃ and MnCO ₃ , in insignificant amounts - oxides, sulfides and hydroxides of Fe, Ca ₃ (PO ₄ ) ₂ , CaSO ₄ .

Limestone: properties and applications

The physico-mechanical parameters of this rock are extremely heterogeneous, but directly depend on its texture and structure. High school students consider the properties of limestone (grade 4) from the position of its external characteristics. They study the following parameters: color, density, strength, condition, solubility. We will go a little further and look more deeply at these properties of the mineral. Limestone has a density in the range of 2700-2900 kg / m ³ . This fluctuation is explained by the amount of contained impurities of quartz, dolomite and other minerals. The volume mass varies over much larger limits. So, for travertines and shells it is only 800 kg / m ³ , and for crystalline rocks it reaches 2,800 kg / m ³ . Considering the properties of limestone, it should be taken into account that the compressive strength of the rock directly depends on its bulk weight. So in shell rock it is only 0.4 MPa, while in Afanites it approaches 300 MPa. The above characteristics of the breed also determine the use of these materials. For example, in the construction of more dense limestone is used for laying walls, and porous is good for facing and creating decorative ensembles.

Exposure to climatic conditions

Depending on the humidity level, the properties of limestone can vary. First of all, this affects its strength - it decreases noticeably if the stone is wet. In addition, most deposits are characterized by heterogeneity of the rock. At this point, it is worth paying special attention, since the heterogeneous material will have different density, which, in turn, can lead to destruction. Analyzing the properties of limestone, we should not neglect such a parameter as frost resistance: this significantly affects the strength of the mineral and the duration of its use. Thus, in crystalline limestones frost resistance is 300-400 cycles. However, this figure is markedly reduced in the presence of cracks and pores in the material. Thus, all the mentioned properties of limestone must be taken into account when using this natural material in order to prevent its destruction.

Limestone in construction

The construction industry is the main consumer of the mineral in question. Dolomitized (rock) limestone is used for the production of putty and plaster mixes, sealants and other. White limestone is used in huge quantities in decorating and decorating buildings. Shell rock is often found as building blocks, etc. We will not focus on this industry, it is already widely known to everyone. And therefore we go further.

Limestone in modern industrial production

It turns out that this natural material is used in the production of paint and varnish materials, rubbers and plastics. And purified from impurities harmful to the human body, is used even in the food industry. The manufacture of glass is not possible without limestone, since it acts as the main source of calcium. This breed has become indispensable, and most importantly - an affordable component for the production of paper. In everyday life we constantly use such products as pipes, linoleum, tiles, tiles, etc., and we do not know that limestone is also present in all these items. Even plastic production (PP, PVC, shells, lavsans and others) can not do without this raw material. In paints, calcium carbonate is used as the color pigment. As you can see, this material occupies a leading place in almost all branches of production.

Chemical industry

Even such things as a shoe polish, toothpaste, cleaning powder, etc., that we use every day, are limestone derivatives. This raw material is also used in the manufacture of tools used to protect the environment from various types of pollution. On the basis of all of the above, we can safely say that the widely known and accessible material, which is limestone, is the most important element of modern civilization.

Interesting Facts

Great contribution to the development of stone carving made the people of South and Central America. The Olmecs, the Aztecs, the Maya have made significant progress in the ability to make weapons, cutting tools and other household items from chalcedony, obsidian and silicon. Thus, rolls, grain-boxes, mortars, etc. were created by them from basalt, sandstones and limestones. Shock and chopping tools were made of diorite, jadeite, jade and other materials. The main center for processing stone are Maya cities - Tonina and Nebah.