The surface of our planet is full of rocks and a variety of minerals. But, more specifically, 95% of the upper layer of the earth's crust is made up of igneous rocks, also called magmatic. Some are very well known, such as obsidian and granite, but others, surely, you do not know them.
You still don't know them well and are you interested in learning about them? So, keep reading because in this Green Ecologist article we are going to see everything about the Igneous rocks, their types, characteristics and various examples.
Characteristics of igneous rocks
The magmatic rocks They are formed when molten rock in the form of magma cools and the minerals that form it crystallize and entangle their particles. Magma can cool on the surface, as a result of volcanic eruptions, or inside the lithosphere, which is the solid layer of the earth's surface. The vast majority of these rocks are formed under the earth's crust.
Although igneous rocks form a very high percentage of the upper part of the earth's crust, they are usually found under a layer of metamorphic rocks and sedimentary rocks. They have great importance in geology, since their characteristics and composition help to understand the Earth's mantle and its composition, as well as to read past tectonic events.
Classification of igneous rocks and their types
Magmatic rocks can be classified in various ways, although their most general classification divides them according to their origin.
Plutonic or intrusive igneous rocks
They have formed inside the lithosphere. There, the magma cools in a much slower process, giving rise to rocks with large crystals, which can be easily observed. These rocks are transported to the surface by erosion processes or by tectonic deformations. Plutonic rocks get their name from plutons, which are the large magmatic intrusions from which they are formed. It should be said that the heart of the largest mountain ranges is formed by intrusive rocks.
Igneous volcanic or extrusive rocks
They are formed when magma is forced to the surface and cools rapidly. The vast majority of these rocks are created by the effect of volcanic eruptions, and as magma cooling occurs at high speed, the crystals that are created inside the rocks are much smaller, invisible to the human eye. In this type of rocks, the formation of voids or holes left by gas bubbles that are formed in the solidification process is common.
In addition to these two major classifications, we also have the Philonian rocks, which are halfway between plutonic and volcanic, when a magma seam heading toward the surface solidifies midway. The magmatic rocks They can also be divided according to their texture and composition.
You can learn more about volcanic rocks: types and characteristics by reading this other article.
Types of igneous rocks according to their texture
- Vitreous: They are volcanic rocks that are formed by being violently thrown into the atmosphere, where they cool at high speed.
- Aphanitic: volcanic with microscopic crystals.
- Phaneritics: formed when large amounts of magma solidify very slowly and at great depth.
- Porphyry: These rocks have large crystals in the center and small crystals near the outside, due to uneven cooling.
- Pyroclastic: pyroclasts form in explosive volcanic eruptions. They do not have crystals and are made up of rock fragments.
- Pegmatitics: Very coarse-grained, these rocks are made up of crystals of more than one centimeter in diameter. They are formed when magma has large amounts of water and volatile elements.
Types of igneous rocks according to their chemical composition
Igneous rocks can have different levels of light or dark silicates.
- Felsic: They are made up of 70% silica, low density and light colors. The continental crust is made up mainly of them, and they contain approximately 10% dark silicates.
- Andesitic: they contain at least 25% dark silicates.
- Mafic: they are very rich in dark silicates. They are of greater density and of darker colors, and they constitute the oceanic crust.
- Ultramafic: With at least 90% dark silicates, they are rare rocks to find on the planet's surface.
Examples of igneous rocks
In closing, these are some simple ones examples of igneous rocks:
- Granite is the most common plutonic rock.
- Basalt is a widely known volcanic rock.
- Obsidian, widely used by our first ancestors in prehistory, is an igneous rock with a glassy texture.
- Peridotite is one of the rare ultramafic rocks.
- Rhyolite, an extrusive igneous rock, is considered the volcanic equivalent of granite.
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