Rock Definition

A rock is a solid material, formed by natural processes and composed of minerals. There are rocks that can be composed of a single type of mineral, and others by a mixture of different minerals.

Rocks are one of the fundamental components of the earth’s crust and can be found in different forms around the world, from small grains finer than sand to large mountains and rock formations. They can have different physical properties, such as hardness, texture, color and density, and in each case they can vary according to their composition, that is, what type of minerals form it, but fundamentally they vary according to the rock formation process. .

How are rocks formed?

There are three main processes by which rocks are formed: magmatismor igneous formation, the sedimentary formation and the metamorphism. These three forming processes determine a classification in which three main types are distinguished, with very different properties: igneous rocksthe metamorphic and the sedimentary. It is worth mentioning that, within each of these categories, there are different varieties and subtypes that form under different geological conditions and have unique characteristics.

Types of rocks, and their properties: igneous, sedimentary and metamorphic

The igneous rocks They are formed from the cooling and solidification of magma. He magma It is molten rock, in a fluid state, that originates inside the Earth by fusion processes (by heating the rock, which causes it to go into a liquid state, as happens with an ice cube that we leave outside the refrigerator). . Magma forms at depth, but can rise to the surface through volcanoes. When magma rises to the surface, it is known as wash. When the magma or lava cools, it becomes solid rock again, giving rise to igneous rocks. If the magma solidifies below the surface, it forms intrusive igneous rocks either plutonicwhile if lava solidifies on the surface, they form extrusive igneous rocks either volcanic. Some igneous rocks are highly valued as construction elements, such as granite or basalt, likewise, in general, they are the hardest and most resistant forms that exist, and they withstand erosion better than other types of rocks.

The sedimentary rocks They are formed from the accumulation of sediments, such as sand, clay, silt or rock fragments, which are deposited on the Earth’s surface by the action of erosive agents such as water, wind, ice or gravity. Let’s think of a river that carries sand and rounded rocks of different sizes. Over time, a long time, these river sediments accumulate in enormous quantities and under their own weight, they begin to “stick” and compact, they begin to turn into rock (these processes are called compaction and cementation). The rocks originated in this way are called sedimentary. It is the most abundant class on the surface of the earth and they usually have a great variety of colors. They are very frequent reddish, yellow and greenish. The colored layers that can be seen in some mountains are a characteristic of sedimentary rocks, and in arid and semi-arid zones their formations are especially evident. They are soft rocks, sometimes it is possible to break them by hand (with a little force) or with a hammer; and are the least resistant to erosion.

The Metamorphic rocks They are formed from the transformation of pre-existing rocks, either igneous or sedimentary, under conditions of high pressure, temperature or chemical activity. These conditions occur if, for example, the rock is buried, if magma rises (with which the rocks near the magma are subjected to a high temperature). These processes cause its structure to change, producing a whole range of rocks known as metamorphic. The more intense the metamorphism, that is, the more exposed it is to the metamorphizing agent (pressure or temperature), the more it will transform. Thus, low grade metamorphic rocks are very similar to the original rock, while high grade metamorphic rocks are very different from the original rock. If metamorphism affects a sedimentary rock, it becomes harder and more resistant the more intense the metamorphism. For example, clay can be turned into slate, and limestone can be turned into marble.

In general, the geological processes that form rocks are very slow and occur over millions of years, in a geological time scale. However, their observation and study can provide valuable information about the history and evolution of the Earth.

Fossils are remains of organisms, usually bones, that have become rock or marks of organisms’ activity (footprints, caves, tunnels) that have been imprinted on their body. Sedimentary rocks are the only ones that can contain fossils, since when the organism died it could have been buried in the original sediment, which over time became a sedimentary rock and the fossil was left inside. Heat and pressure destroy the remains of organisms, therefore metamorphic rocks can contain fossils only if they are very low grade (that is, they were little affected by metamorphism) and igneous rocks never have fossils.

Rocks as natural resources

Rocks are important natural resources that are used for a wide variety of purposes in different economic sectors. They are used in the construction of buildings, roads, bridges, dams and other structures. Granite, granodiorite and basalt (igneous), sandstone and limestone (sedimentary), marble and gneiss (metamorphic) are some examples of its use in construction. Some rocks contain valuable minerals, such as gold, silver, copper, iron. Mining is an important activity for the extraction of these minerals, and rocks are the primary source of these resources.

Coal, which is a sedimentary rock of biological origin, is used for electric power generation in many parts of the world. Due to their mineral content, rocks are an important source of nutrients for plants. Limestone, for example, is used to correct the acidity of the soil and improve its quality.

In short, they are important resources for a wide variety of industries and economic sectors. Its extraction and responsible use is essential to guarantee its availability in the future.

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