The petrology It is the branch of geology that studies rocks, their origin, composition, physical and chemical properties and distribution in the planetary crust. The term comes from the prefix Petro= stone and logos= study.
Petrology has a literal meaning equal to the term lithology (lithos= stone), in fact they have sometimes been used as a synonym. However, there are certain differences, since petrology studies everything related to rocks or stones. Whereas lithology concentrates on the rock composition of a given area.
Petrology is divided into specialized areas or branches of the discipline, depending on the type of rocks being studied. So there are two branches, the petrology of sedimentary rocks or exogenous petrology and the petrology of igneous and metamorphic rocks or endogenous petrology..
Branches of petrology are also developed according to the proposed objective for the study of rocks. In such a way, that there is petrography for the description of rocks and petrogenesis to determine their origin. Like applied petrology that focuses on the geological properties of rocks.
Petrology is a science of the utmost importance, since rocks constitute the fundamental support of human physical structures. Just as they are also essential raw material for a large part of human industrial activity.
The interest in rocks has always been present in the human being, since it is a constant element in its natural environment. In fact, the first human tools were made of stone and gave rise to an entire age of humanity, known as the Stone Age..
The contributions to arrive at a rock science have been multiple and of diverse cultures, among them the Chinese, the Greek and the Arab. In the western world the writings of Aristotle stand out and especially the work of his disciple Theophrastus called Perì Líthon or About the Stones.
However, the origin of petrology as a science is closely linked to the origin of its mother science, geology. In fact, geology as a science is considered to be consolidated in the 18th century, when its principles were established..
Thus, it is at the end of that century when petrology arises, as a result of a scientific controversy that developed in relation to the origin of rocks, between two groups called the Neptunists and the Plutonists.
The Neptunists argued that the rocks originated from the sedimentation and crystallization of minerals from an ancient ocean that covered the planet. Hence the name of his position (Neptunists), alluding to the Roman god of the oceans Neptune.
The father of the Neptunist position is considered to be the German scientist Abraham Gottlob Werner. Furthermore, Wener in his work Brief classification and description of the rocks (1787), laid the foundations for a new model of geological classification.
Meanwhile, the plutonists explained the origin of rocks from magma in the deep layers of the Earth by high temperatures. For this reason they were called plutonists, alluding to the Roman god of the underworld, Pluto.
The father of plutonism is the Italian naturalist Anton Lazzaro Moro, who was also the first to separate rocks into sedimentary and volcanic or igneous. Later, Moro's theories were incorporated by James Hutton, founder of modern geology, in his uniformitarian theory..
In this theory Hutton described the origin of rocks as a combination of continuous erosion processes and high pressures and temperatures. James Hutton's main work was Theory of the Earth (1795).
Finally, modern knowledge allows us to understand that both positions had to do with reality. Sedimentary rocks arise by processes related to the intuitions of the Neptunists. While igneous and metamorphic rocks have their origin in processes coinciding with the ideas of the Plutonists.
Petrology encompasses the study of rocks, that is, everything related to these structures. It includes their origin, the processes that produce them, the site of the lithosphere where they are formed, and the age of the rocks..
Likewise, petrology studies the components and physical and chemical properties of rocks, as well as their distribution in the earth's crust..
Today, petrology includes the study of both terrestrial and extraterrestrial rocks, that is, rocks from outer space. In fact, rocks from meteorites and the Moon are studied.
Rocks are classified into three basic types according to the processes that give rise to them, being sedimentary, igneous and metamorphic. The former form in relatively shallow areas of the crust and the other two types originate deeper..
Therefore, depending on the area of origin of each type of rock that petrology studies, there are two branches of this discipline:
This branch studies those rocks that originate in the shallowest layers of the earth's crust, that is, sedimentary rocks. These rocks are formed from the compression of sediments, which are deposited over millions of years on the surface of the planet..
This occurs especially at the lowest altitudes, that is to say in lakes and oceans. The successive layers are crushing and compressing the lower sediments, which together with chemical processes, hardens said sediments forming rocks.
Unlike sedimentary rocks, the other two known rock types are formed in the deep layers of the earth's crust and mantle..
In the case of igneous rocks, they originate from magma that comes from the mantle at high temperatures and pressures. The magma rises due to internal pressure through the cracks and cools, forming rocks. This occurs mainly when volcanic eruptions occur and large amounts of magma come to the surface in the form of lava..
Finally, metamorphic rocks are those that originate from igneous or sedimentary rocks subjected to great pressures and temperatures. That is to say, rocks that are found at great depths, be they sedimentary or igneous, are deformed or altered by great pressures. This causes changes in its structure and even in its composition..
On the other hand, there are also branches of petrology defined by the objective of the proposed study.
Rocks constitute the structural base or support of most human activities, since they make up the earth's crust. All human infrastructure such as buildings and roads are supported, beyond the ground, on a rocky base.
In fact, in order to carry out any construction project, a geological, specifically petrological study is required. That is, it is necessary to know what rocks exist in the subsoil, their load capacity, as well as their properties..
Otherwise, there is a risk that the future construction will lack the necessary solidity and a collapse will occur. Even more so when it comes to drilling, either in wells or tunnels, since in this case the rocks present are determining elements.
Petrology is also important in that it makes it possible to know the composition and physical and chemical properties of rocks, which throughout history has allowed them to be used as industrial raw materials.
In this sense, petrology is a fundamental element in prospecting studies to find mineral, water, oil or gas deposits..
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