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Learning About Igneous Rocks As inhabitants of this earth, it is our responsibility to learn as much as we can about the earth that we reside upon. Learning about the earth we live on includes learning about the different types of rocks that make up the earth. Sometimes it can seem like learning about rocks and other subjects related to the physical sciences can seem boring. However, learning about different kinds of rocks does not have to be boring; it is often very interesting and engaging. We will begin our discussion about rocks by introducing the 3 main types of rocks. The 3 main types of rocks are igneous, sedimentary, and metamorphic. Let’s start with igneous rocks. Igneous rocks are formed when magma from volcanoes and the earth’s core cool.

How Igneous Rocks are Formed The process of the formation of these rocks is an exothermic process, which means that heat is lost in the process of the rock formation. The magma changes from a liquid to a solid in its transformation into an igneous rock. Igneous rocks have many different shapes and forms. The way igneous rocks are named is based on their composition and their texture. The texture of an igneous rock refers to how large the individual grains are in the final, solid rock. Usually the size of the grains depends on how fast the magma cooled when it was forming the rock. Generally, the slower the magma cooled, the bigger the grains are going to be in the final rock. If the grains are large in the rock, it can be assumed that it cooled within the earth’s crust, and is referred to as intrusive. For rocks that cooled near a volcanic eruption, the grains are going to be smaller and therefore referred to as extrusive. There are many different sizes of grains in igneous rocks.


Texture and Composition of Igneous Rocks Igneous rocks with large grains are referred to as phaneritic. Granite and gabbro are examples of common igneous phaneritic rocks. Igneous with small grains are referred to as aphanitic. Basalt is one of the most common examples of an igneous aphanitic rock. There are also many different types of rocks that are difficult to classify in either category, which complicates the classification. However, these are the two most widely used categories for classifying igneous rocks according to their texture. The other way that experts classify igneous rocks is by their composition. The composition of these rocks refers to the elements that are in the magma that affect the composition of the new rock when it is forming. Magmas that are associated with crustal spreading are generally referred to as mafic. If the magma erupts at the surface, basalt will emerge. If the magma doesn’t make it out of the chamber, then gabbro will emerge. Basalt and gabbro are examples of 2 igneous rocks that are compositionally the same, but texturally different. If your interest in rocks prompts you to learn more, perhaps you would be interested in a rock quarry for sale. Chaparral has a rock quarry for sale in Nevada that you can purchase rock from. Photo Credit: NASA Goddard Photo and Video, Paul Bica, Monado

Learning About Igneous Rocks  

As inhabitants of this earth, it is our responsibility to learn as much as we can about the earth that we reside upon. Learning about the ea...

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