Igneous rocks


On the surface of planet Earth it is possible to find many different types of rocks, each with its own properties and characteristics. All are important because together they make up the earth’s surface . One of the most common types to find and that in fact can be found in greater proportion are igneous rocks , also known as magmatic rocks .


What are igneous rocks?

Igneous rocks are the rocks that are formed from the cooling and solidification that occurs in magma and that is also located inside the planet. When magma reaches the surface of the earth it solidifies giving rise to igneous rocks.

  • Characteristics of igneous rocks
  • How they are formed
  • Components (edit)
  • Classification of igneous rocks
  • Structure
  • Texture
  • Density
  • ID
  • Use
  • Deposits
  • Examples of igneous rocks

Characteristics of igneous rocks

Among the main characteristics that can be found in igneous rocks we can mention the following:

  • Most of the igneous rocks form under the crust of the Earth .
  • They are found mostly under metamorphic and sedimentary rocks .
  • They help scientists understand the Earth’s mantle .
  • They have a very high level of hardness and resistance .
  • They can be formed from magma or by a series of internal intrusive processes .
  • They do not allow accumulation of fossils or organic matter .
  • They have a fairly variable proportion of crystallized matter .

How they are formed

This type of rock is formed from magma which is located in the earth’s mantle , which at the same time is recycled when the renewal process occurs in the earth’s crust . This magma, manages to rise to the surface from the deepest layers and little by little it begins to solidify, forming crystals and igneous rocks located below the crust.

These stones later begin to cool slowly and this determines the type of crystallization they undergo. During its formation, all the stages of cooling will slowly crystallize the minerals and in this way igneous rocks originate. On some occasions, this magma can be violently expelled to the surface of the earth at the time of a volcanic eruption , causing the rocks to cool more quickly.

Components (edit)

The main components of igneous rocks are silicates and among them we find calcium, sodium, potassium, iron and magnesium, materials that also make up approximately 98% of magma. Once these materials are able to cool down, they combine, thus giving rise to two different groups of components.

  • Dark silicates : they are also called ferromagnetic and are minerals high in iron, silica and magnesium.
  • Clear Silicates – These minerals have considerable amounts of potassium, sodium, iron, magnesium, silica, and calcium.

Classification of igneous rocks

Magmatic rocks can be classified into two different types. Rocks Intrusive or plutonic as well known are those formed within the Earth when magma manages to reach the earth’s crust, it takes them a little longer to form and be consolidated. This type of rock is brought to the surface thanks to different erosion processes or through tectonic deformations .

On the other hand, extrusive rocks are those that solidify on the earth’s surface after the magma has been expelled to the surface thanks to different volcanic processes . They can also be classified as Philonian rocks , a middle term for magma that goes to the surface but manages to solidify along the way.


In the case of igneous rocks, the structure will depend on the way in which the crystals and the amorphous materials that compose them are ordered, also including their shape and size. Their size can vary and depend on whether their crystals can be seen with the naked eye or not. In this way, we can say that intrusive igneous rocks can have a granitic , apolytic , pegmatitic , porphyroidal or extrusive structure .


The texture of igneous rocks can vary significantly and for this reason, they can be classified depending on the texture of various types of rocks.

  • Aphanitic : they are volcanic stones whose crystals are microscopic and are of the volcanic type.
  • Vitreous : they are formed from volcanic rocks that are thrown into the atmosphere at great speed.
  • Phaneritic : they have large crystals in the center and some smaller ones on the outside. This occurs because when they are able to cool they do so unevenly.
  • Pyroclastic : they are formed when volcanic eruptions occur explosively.
  • Pegmatitic : its crystals measure more than one centimeter and are formed when the magma comes into contact with water and some volatile elements.


Igneous rocks are natural terrestrial materials and, as such, they can have a great variability in terms of their density. However, they typically have intact densities ranging from about 2650 kg / m3 to over 2900 kg / m3.


In order to identify an igneous rock it is important to observe its texture and see if it has bands , layers or vesicles which are a type of air vesicle. It is important to remember that these rocks can have a glassy or foamy appearance, they can be porous or full of bubbles . Its structure can be observed in a crystalline way and its density is usually higher than other types of rocks. Some may have small black splashes and are light enough to allow them to float .


Igneous rock has many uses, one of them is for methods of analysis and studies on the composition and formation of the mantle that forms the Earth. This type of rock is used mainly for the manufacture of floors and in construction projects . However, its uses may depend on the formation process that the rock has, its mineral content, its hardness, texture and its properties. Some rocks can be used to create work surfaces tiles, and coatings .


The deposits of igneous or magmatic rocks can be classified and found in two important groups. The first of them is the primary deposit where the rocks that have not yet been taken or transported from the place of origin to a different one or where we find those rocks that have not been fractured by means of tectonic events . The second deposit is the place where the rock has been taken and in many cases they are welded to the ground because due to their high temperature when they come into contact with other fluids or substances they harden.

Examples of igneous rocks

Some examples of igneous rocks are as follows:

  • Granite which is one of the most common
  • Basalt
  • Obsidian
  • Peridotite
  • Rhyolite
  • Dacite
  • Greenstone

Leave a Comment