In the bowels of the earth is almost the entire periodic table. Chemical elements form among themselves the compounds that make up natural minerals. One or more minerals may enter the rocks of the earth. The article will try to deal with their diversity, properties and value.
What are rocks
For the first time this term was applied by our Russian scientist Severgin in 1978. The definition can be given as follows: rocks are a combination of several minerals of natural origin in a single whole, having a constant structure and composition. Rocks can be found everywhere, since they are an integral part of the earth's crust.
If you study the description of rocks, then they all differ in signs:
- Density.
- Porosity.
- Color.
- Durability.
- Resistance to severe frosts.
- Decorative qualities.
Depending on the combination of qualities, they find application.
Rock variety
The subdivision of rocks into different types is based on the chemical and mineral composition. The name of the rocks is given depending on their origin. Consider what groups they are divided into. Common classification may look like this.
1. Sedimentary rocks:
- clastic rocks;
- organogenic;
- chemogenic;
- mixed.
2. Magmatic:
- volcanic;
- plutonic;
- hypabyssal.
3. Metamorphic:
- isochemical;
- metasomatic;
- ultrametamorphic.
Next, we consider in more detail the characteristics of these rocks.
Sedimentary rocks
Any rocks, being under the gun of various factors and external processes, can be deformed, change their shape. They begin to collapse, fragments are carried, can be deposited at the bottom of the seas and oceans. As a result, sedimentary rocks are formed.
It is difficult to classify rocks of sedimentary origin, since most of them were formed under the influence of many processes; therefore, it is almost impossible to attribute them to a specific group. Currently, this type of breed is divided into:
- Clastic rocks. Different examples can be given: everyone knows gravel or crushed stone, sand and clay, and many others.
- Organogenic.
- Chemogenic.
Let us dwell in more detail on each type of breed.
Clastic rocks
They appear as a result of the formation of debris. If you classify them according to their structure, then distinguish:
- Cemented rocks.
- Uncemented.
The first variety in its composition has a connecting component, which can be represented by carbonates, clays. The second variety does not have such substances, therefore, it has a loose structure.
It can be further clarified that clastic rocks often include traces and remains of plant and animal organisms. These include shells of mollusks, preserved petrified parts of the stem, and wings of insects.
Clastic rocks are best known. Examples confirm this. All known sand and clay, crushed stone and gravel, as well as many others, are detrital. All of them are widely used in the construction industry.
Chemogenic breeds
This group is a product of chemical reactions. Salts, such as potash, and bauxite can be attributed to them. The formation of this type of rock can go in two ways:
- Gradual process of concentration of solutions. The influence of radiation from the sun is not excluded here.
- Compound of several salts at a low temperature.
The structure of such rocks will depend on the place of their appearance. Those that are formed on the surface of the earth have the form of a layer, and the deep ones are completely different.
Rocks are very widely used from this group, examples only confirm this. Chemogenic rocks include:
- Mineral salts.
- Bauxites.
- Limestones
- Dolomite and magnesite and many others.
In nature, rocks are quite common, in the formation of which various natural processes took part. The name of the rocks that occurred in this way is mixed. For example, you can find sand mixed with clay.
Organogenic sedimentary rocks
If debris rocks sometimes include in their composition the remains of living organisms, then this group consists only of them. It includes:
- Oil and shale.
- Bitumen.
- Phosphate rocks.
- Carbonate compounds, such as chalk, which is written on the blackboard.
- Limestones
If we talk about the composition, then limestone and chalk are almost entirely composed of the remains of the shells of ancient mollusks, foraminifera, corals, and algae are also part of them. Considering that different organisms can give rise to an organogenic breed, then they are divided into several varieties:
- Bioherm. So-called clusters of living organisms.
- Tanatocenoses and tafrocenoses are the remains of organisms that have long lived in these places or were brought by water.
- Planktonogenic rocks formed from organisms that live in water bodies.
Grain of sedimentary rocks
This feature is one of the characteristics of the structure of sedimentary rocks. If you look at the rocks, they can be divided into homogeneous and inclusive. In the first embodiment, the entire breed is perceived as a homogeneous mass, and in the second one can consider individual fractions, grains and their shape and ratio.
If we consider the size of the fractions, then we can distinguish several groups:
- The grains are quite clearly visible.
- Concealed visually seem structureless.
- In the third group, it is impossible to consider granularity without special equipment.
The form of inclusions may be one of the criteria by which these rocks are separated. There are several types of structures:
- Hypodiomorphic. In this type, crystals obtained from solution act as grains.
- The hypidioblast type refers to an intermediate structure in which redistribution of substances occurs in an already hardened rock.
- Granoblast, or sheet, has irregular crystals.
- The mechanical conformer type is formed as a result of mechanical action of grains under pressure of those layers that are located above.
- Non-conformal-grained has the main feature in the form of various outlines of grains, which leads to the appearance of emptiness and porosity.
In addition to structure, texture is also distinguished. The division is based on layering:
- Graduation. Its formation is carried out at great depths under water.
- Interlayer occurs in some layers of water, clay primers, layers of sand in clay can be attributed to this type.
- Interlacing occurs with a large layer thickness; one can observe a change in the color gamut of the layers. An example is the alternation of clay and sand.
Many more classifications can be given, but we will probably dwell on this.
Representatives of sedimentary rocks
We have already examined sedimentary clastic rocks, we have also given examples of them, and now we will focus on others, which are also widespread in nature.
- Gravelites. They are sedimentary rocks in the form of gravel. They include fragments of rocks and minerals of various sizes.
- Sand rocks. These include sands and sandstones.
- The silty rocks are somewhat reminiscent of sandstones, only in their composition have more stable minerals in the form of quartz, muscovite.
- Siltstone is characterized by the presence of roughness at the fracture, and the color depends on the cementing material.
- Loam.
- Clay clay.
- Mudstones.
- Mergels are a mixture of carbonates and clay.
- Limestones that are composed of calcite.
- A piece of chalk.
- Dolomites resemble limestones, but instead of calcite, dolomite is included in their composition.
All these rocks are widely used in construction and other sectors of the economy.
Metamorphic rocks
If we recall what metamorphosis is, it will become clear that metamorphic rocks appear as a result of the transformation of minerals and rocks under the influence of temperature, light, pressure, water. The most famous of this group are: marble, quartzite, gneiss, slates and some others.
Since various types of rocks can undergo metamorphosis, the classification depends on this:
- Metabasites are rocks that result from the conversion of igneous and sedimentary rocks.
- Metapelites are the result of the conversion of acidic sedimentary rocks.
- Carbonate rocks, such as marble.
The shape of the metamorphic rock is preserved from the previous one, for example, if before the rock was located in layers, then the newly formed one will have the same shape. The chemical composition, of course, depends on the source rock, but can change under the influence of transformations. The mineral composition may be different, and it may include either one mineral or several.
Igneous rocks
This group of rocks makes up almost 60% of the entire earth's crust. They arise as a result of melting of rocks in the mantle or in the lower part of the earth's crust. Magma is a molten substance partially or completely enriched in various gases. The formation process is always associated with high temperature in the bowels of the earth. The geological processes taking place inside the earth constantly provoke magma to rise to the surface. In the process of raising, the cooling and crystallization of minerals takes place. This is the process of formation of igneous rocks.
Depending on the depth at which the solidification occurs, rocks are divided into several groups, the table of varieties may look like this:
| Plutonic | Volcanic | Hypabyssal |
| Such rocks are formed in the lower part of the earth's crust. | Formed during the eruption of magma to the surface. | A rock appears when magma fills cracks in existing rocks. |
Igneous rocks differ from clastic in that they do not contain the remains of dead organisms. Granite rock formation is one of the most famous among this group. It consists of feldspar, quartz and mica.
When a volcanic eruption occurs, then magma, emerging on the surface of the earth, gradually cools down and forms rocks of a volcanic type. They do not contain large crystals, as the temperature decreases quite quickly. Representatives of such rocks are basalt and granite. They were often used in antiquity for the manufacture of monuments and sculptures.
Volcanogenic clastic rocks
In the process of volcanic eruption, not only the granite rock formation is formed, but also many others. In addition to the outpouring of lava, a large number of fragments fly out into the atmosphere, which, together with clumps of solidified lava, fall to the surface of the earth and form tephra. This pyroclastic material is gradually eroded, part of it is destroyed by water, and the one that remains is compacted and turns into strong rocks - volcanic tuffs.
On the fault of these rocks, fragments can be seen, the gaps between which are filled with ash, sometimes clay or siliceous sedimentary substances.
Rock weathering
All rocks, being in nature, are exposed to many factors, as a result of which weathering or destruction occurs. Depending on the impact, there are several types of this process:
- Physical weathering of rocks. It occurs due to temperature changes, as a result of which the rocks crack, water gets into these cracks, which can turn into ice at negative temperatures. So gradually the destruction of the rock.
- Chemical weathering is carried out under the influence of water, which enters the rock cracks and leaches, dissolves it. Marble, limestone, and salt are most susceptible to such effects.
- Biological weathering is carried out with the participation of living organisms. For example, plants destroy the breed with their roots, lichens that settle on them secrete some acids, which also have a destructive effect.
It is almost impossible to avoid the weathering of rocks.
Rock value
It is impossible to imagine a national economy without the use of rocks. Such an application began to be carried out in ancient times, when a person learned to process stones. First of all, rocks are used in the construction industry. Examples include the following:
- Marble.
- Limestone.
- A piece of chalk.
- Granite.
- Quartzite and others.
Their use in construction is based on strength and other important qualities.
Some rocks find their application in the metallurgical industry, for example, refractory clay, limestone, dolomites. The chemical industry is inseparable from rock salt, tripoli, diatomite.
Even light industry uses rocks for its needs. In agriculture, you can not do without potassium salts, phosphorites, which are an important component of fertilizers.
Thus, we examined the rocks. And we can conclude that at present they are the indisputable and necessary helpers of a person in almost every industry, from everyday life to construction. That is why the term is most often used not as a rock, but as a mineral, which accurately expresses the significance of these natural deposits.