The rocks are a natural group of minerals consolidations are part of the crust of the earth and were caused by different geological processes . There are several types of rocks on the planet and among them we find sedimentary rocks which owe their formation to precipitation and the accumulation of minerals.
What are sedimentary rocks?
Sedimentary rocks are a type of rock that is formed from a group or set of sediments which are mobilized by air or water or by the compaction of the remains of living beings which can form hard rocks.
- Sedimentary rock characteristics
- How they are formed
- Components (edit)
- Classification of sedimentary rocks
- Examples of sedimentary rocks
Sedimentary rock characteristics
Many characteristics can be found or observed in sedimentary rocks, some of the most important are the following:
- They are covering more than the 75% of the total of the surface of the earth.
- They can be formed in valleys , ravines , lakes, and seas .
- They have a structure in the form of a stratum .
- Its layers are produced progressively thanks to the sedimentation process .
- They have an intermediate degree of permeability .
- They usually have wavy marks or small oval-shaped ridges .
- They can be formed from the remains of living beings .
How they are formed
It is important to understand that these types of rocks are formed on the surface of the earth , many of them from rocks that already exist and that undergo a sedimentary process . This process, responsible for forming the rocks, has three general phases which are mentioned below.
- Erosion : it can be chemical, biological or mechanical and in the process the rock is destroyed, causing it to break down into smaller pieces. This process can be produced by water, wind or ice.
- Transport : in this stage, the water or the wind are responsible for carrying all the materials that have been produced as a result of erosion.
- Deposit : here, all the sediments that were transported accumulate in more depressed areas such as basins or pits.
- Compaction and diagenesis : they are a series of chemical and physical processes whose function is to make the rocks compact, finally transforming them into sedimentary rocks.
Sedimentary rocks are composed of several components, including fragments and minerals . The three main components are known as ortho chemicals , Allochems and Terrigenous . Orthochemicals are compounds that are formed through chemical precipitation that occurs in the sedimentation basin either during or after the remains are deposited.
Allochemicals are materials that have a chemical or organic origin and manage to reach the area as fragments and most of them are composed of calcium carbonate. In the case of the terrigenous components, we find fragments of rocks and crystals that come from the alteration or disintegration of rocks.
Classification of sedimentary rocks
Sedimentary rocks can also be classified into various types, always depending on the way they were formed or the composition they have. In this way, we can say that their classification according to their way of training is as follows:
- Detrital sedimentary rocks : they are also known as clastic and are formed through the accumulation of sediments from the erosion of other rocks located in mountains and that are deposited elsewhere by means of the force of gravity . In this group we can find clay rocks and sandstones.
- Organogenic rocks : they are formed from the remains of living beings and it is the type of rock that we can observe when the skeletons of animals are bio mineralized. They can also be formed from cellular matter and in this case they are known as organic rocks.
- Marls : they are mixed sedimentary rocks that are composed of chemical and detrital rocks .
Depending on the composition of the rock, they can also be placed within the following classification.
- Carbonatic : they are made up of carbon and are a very large group, making up about a third of the rocks.
- Organic : are those that are formed by organic matter.
- Siliceas : they are made up of particles of the mineral silicon or they can be formed from the weathering of granite.
- Terrinogen : they are formed from granite or other siliceous particles.
- Ferro – aluminum : these rocks are formed from the weathering process that an ore undergoes after a volcanic eruption .
- Phosphatic : this is a type of rock that is not common because it is formed from the excrement of birds.
Regarding its structure, we can see that sedimentary rocks have a large number of strata located in parallel, mainly horizontal, although this can vary depending on the effect of deformation forces or fractures that the rocks have suffered. Its internal structure can vary considerably and that varies from rock to rock, it also depends on its origin and the minerals that compose it. In this way, you can find two types of internal structures which are:
- Cross stratification : when the particles that make up the rock are found as inclined sheets.
- Granoselección : in this case, the structure of the grain that forms the rock is much greater than the stratum and this causes it to become finer than progressive.
When we talk about the texture of sedimentary rocks we talk about all the characteristics that the components of their sediments have, this includes their shape, their disposition , porosity and permeability . They can have a classic texture type , a crystalline texture, or both .
Most sedimentary rocks have densities ranging from 2.2 to 2.7 g / CC , however this amount can vary depending on the rock.
In order to identify sedimentary rocks, it is necessary to observe their sediment layers as well as the components that make them up. It is also important to know if the rock comes from the sea or from the water as these can be altered. Being able to find and determine if there is limestone in them is important as well as if they have the presence of fossils .
Various types of sedimentary rocks can be used to make different medicines . Petroleum can also be obtained from them and from this, make plastics , synthetic fabrics and PVC , to mention a few examples. The manufacture of cement comes from sedimentary rocks such as limestone, as well as the manufacture of marble floors that comes from the rock with the same name.
They can be used for the manufacture of plaster , mortar , quicklime , chalk and rubber . Industrial use is one of the main aspects for this type of rocks, the manufacture of clay, bricks, gravel and sand are some of the most important uses.
Sedimentary rock can be found in two different types of deposits, one is the allochthonous sedimentary deposit and the other, the autochthonous sedimentary deposit . In the case of allochthonous deposits, we find three different places:
- Riverine and alluvial delights
- The deposits located on the beaches
- The fossil delights
In the case of autochthonous deposits, the rock can be found in:
- Residual deposits
- Sedimentary iron deposits
- Manganese sedimentary
- Evaporites or marine
Examples of sedimentary rocks
Some examples of sedimentary rocks that we can find on our planet are the following: